7 ! A BAOTEiUOLOGICU SURVEY <IF -'lIU) PRACTICES USED

" BY A LOCAl, CR:Wjl'lP-Y ill HAlIDLIJIG A!lll

lU.!lUnCTIlUIIlG-.:il.Ui!t PllODUCTS

" --

Subml tted to the

D.\IRY HUSBANDRY DErARTMEnT

VI RGINIA POLYTECPJrIC INS~ITUTE

~IACK3BURG, VIRGINIA

AS A.

KIlIOR THESI S

FOR THE

P RUA.L FI1LFILLl!.&1l~ OF T~ REQUIREliEIITS

~'Os l'llE DSGilEE OF lUSTER OF SOIENCE

•

3ubml tted by:

,'" ~,y~

IIORACE E. ALPHIIl "I

~LACK3~URQ. VIRGINIA

KAY 15, 1935

·y .... .... ..:

,.

•

ACKl!OVlLElXllIEft

~he author w1shes to express h1s sincere

appreciation to Professor C. VI . Holdaway, under

whose superv1sion the work was oonductod.

Thanks are also due Proressor A. B. »as8ey

for h1s 8U68est1ons and valuable assistance.

UBLE OF COIITElIfS

Introduct1on. .. . . ... ... . .. . ... .. . . ... . . . .. ... ....• 1

Rey1ew of L1 tera l.'Ul"e •.• .•••. I , • • • • • • • • • • • • • • • • • • • • 3

Pro sent Study' . .• It-. • • • • • • • • • •• • • • • • • •• • • • • • •• • • • • • • 4

PART I. Determining the In1'lueno6 of the Mllle Cans and llottles Oll tho llaoterlal OOlltent of Mille:

~ethod of cleaning the anna.............. 5

Counting the number of baoter1.... .. ....... 6

Results ... ..... . ........................ . 6

~etho4 or Cleaning Bottles... .. ............... 8

Results .•. ,.............................. 9

PARr II. Det .. "",in1ng the Souroo of llaoter1". and the uethod of Oonta~in .. tion During tho ProoeeDing of Fluid Mille ••• •••••••••• ••• 11

Colleot1l1€ anmplea .•................•.•• t 11

Uethod of oounttng baetel'ia........... . .. 12

ProoesIJ1ng of 11ilk "All ••••••• .• • •••• , • • . •• • • •• 15

Cleanins utensils .. . . . . . . . . . . . . . . . . . . . . . . 14

Results .. " . ........................ , ...•. 15

... Inf11l8noe of pumpina on the baoterial eontent .•.•.••.. .... ••• 20

b. Col lective influence of heater Bn.d. :til ter. . . . . . . . . . . . . . . . . . • . . . . 20

o. Influence of past.urization •.• • .••• 21 d. Influenoe of cooler • ••••... . ..• •••• 22

ProoeeDing of lt1lk ttB".................. . ...... 23

Colleo tine; samploD....................... 23

Reaul ta. • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • .. 24

Table of Content~ ~2-

~ . Influenoe of the Dasteur1zer ... ...... I • • • •• ...... 28

b. Influence ot cooler •••..........•• 26 o. Influenoe of the bottle f iller • . •• 28 d. Collective influence of the

utensils .... . .. ~"""' " ...... 29

Ef:teot of Agi tatlon . ...... . . . .... .. ...... , . . • 30

Resu.lts .... . ............ . . . .... .... , ... . 32

PARr III . Determ1ning tho Yeast, Yold and Bacter1al Oontent of Cream DIlr1ng t he Various Operut1ons 1n :Bu.tter-lIak1llg_. ... .•.•..• .•••. ... •• . .• 35

H1stor1oo.1.. . . . . . . . . . . . . . . . . . . • . . . . . . . .. 56

Kethod of study _ .. .. ... . . .......•... _. • • 06

Colleoting Sa.:m~lee.... .... ... . .. ..... . .. as

Rewlts.. ... . . ... .. . . . . .. . . . . . . . . . .. .. . • 39

Detormin1ng the Eff •• t of O~bon Dioxide on t he NUmber o:f 1I1oroorga.ni .... e Found in Bi:ltter and Cream.................... .. ...... 40

Reoults obtained afte~ trea tment with oe.rbon d1ox1de ....• ~ . .. . . . .. .• 41

P~RT IV. Iletormln1ne the Influence or V"r1oUD Operat1ons on the Baoter1al Content ot loe Cree.m............................... ... .. 43

PreYioua studies...................... .. .... 4r4

Jiethods used. .. . . . . . . . . . . . . .. . . . . . . . . . . . .. . 45

Kost frequent souroes or oontam1nation.. 46

Table ot Contents -3-

Results ........ .. ............. .... " .......... 47

a. Influence ar pastourizatlon on the bacterial oontent of t he 100 or0am mix. I ....... ......... ••• ••• 49

b. Influenoe at homogen1zation upon tho baoteria l oontent ot an ice creu.m mix ........................ 50

0. Influenoe of oooling the ice cream mix on the baoterial content .•. ....................•. " 50

d. Influenoe of ag1ng on the baoterial content of the 10e o ream. mix •. • ..• ...• I • • • • • • • • • • • • •• 51

8. Influenoe of free~ing on the baoteri a l oontent of an ice cror..m mix ..•..... ................ ~. :52

Conalu.s1ollS ......... .•.... . •....•............•... ... 53

131 bl1oaraphy. . . • . . . . . . . . . . . . . . . . . . • • . . . • . . . . • . . . . .• 05

A BACTERIOLOGICAL SURVEY OF THE PHACTI03S USED

:BY A LOOAL CHEAlfllRY IN H,l.}IDLING AJiD

lI!A.IIUFA.C'l'URIl'!G DAIliY PllODUCTS

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IlTTROllUOTIOI1

Uodern dairy prnotioe in subJeot to ma~

resulations designed to prevent a produot being de­

livered to the oonsumer 1n an unsanit .. ry oondition.

Large numbera of baoteria do not neoessarily oondemn

f ood products, but usual~"" exoessi vo number of ,~

baoter1a 1s assooiated with 1nf~ior materials and

unean1tary praotioes. Definite losal limits of the

number of baoter1a permiss1ble in the m1lk supply have

been established by tho heal th authorities, and the

burden rests pr1mar1ly upon the retailer to observe

them.

If the distributor 1s to mnintain the h1ghest

standards of keoping quality 1t is eeeential for 111m

to have nome knowledge of the bacter1al aotion going

on in the pasteur1z1ng, 00011nS, and bottling prooess­

ea. ~he main faotor 1n protecting the keeping qus11ty

of milk becomes one of prevent1ng the entrance of

bacteria , of destroying them after the¥ enter. or of

keeping them at 11 10" temperature to checlc their

groNth. The f1rst interea t of the distributor ahould

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be to restrict the number of bacteria getting into

the milk, so l ong as is praotical with the expense in­

volved. The probl em of plant contamination oan be

most eoonomicall¥ approached by making an extensive

survey of the product from the time it enters the

orellJlleT¥ until it is read¥ for del1veT¥.

The survey was made to show the influence

that the various manufaoturing operations exert on th.

baoterlal content of fluld ml1k, butter, and 10. cre8m.

It is reasonable to suppose t hat some parts ot the

prooessing equipment are grester baoterial oontributors

than others. It the plant operator had 80m8 knowled,ge

of the most abundant sources of contaminat1on, he oould

make an effort to keep the number of bacteria to a

m1nImum. by exercis1ng greater oare in oleaning and

ster1lIzing the utens11s.

An¥ weak or unsatistactoT¥ praotlces found in

the plant wl1l be 1nvestigsted and a probable means of

control w11l be sought.

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REVI.&l OJ? LITl£RA.TURE

A review of available litel~ture Deems to

1ndioate that little attention has been given to either

the absolute or relative importance of ~ givnn d&1r,r

operation. The surveys that are most fre quontly made

are those oonduotod to determine the spread of epi4emios

whioh .. re often attributed to the milk supply.

In 1890. llaokha.ua and Cronhelml observed that

mllk p~s9ing over a oerta in oooler rained its germ oon­

tent from 11,500 to Z3,OOO baoterin per cub1c centimoter.

In 1904, Bergey2 concluded from his stUdies on milk oon­

t am1nation that the greater portion of the baoteria with

"hloh milk booomos oontaminated is derlved trom the

utensils.

Russel and Hoffman3 found that when milk bottles

were washed, steamed and allowed to stand twenty.four

hours, the baoterl a mult1plied in the water result1ng

~rom the oondensation of the steam. Tho studies of

Prucha and l1etter4 roved the tact that it io possible

to produoo milk wi th a germ oontent or less than 10,000

baoteria per oubio oentimotor, when t he utensils are

properl y cloaned. Conn5 stated that t he vessels 1n

whioh 101lk and oream are to be kept are great souroes

or baoter i nl oontaminatlon. The small germs gather ~on

the sides and joints of the venael and develop in minute

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por~ions ot milk which ~e dlttlcult to de8~ro7 by

waBh1llB.

Eardi"66 makes the to11O'/1i"6 ata tement as to the

purpose ot " similar investigation. "When health offioials,

t&11i"6 to t1nd other meane ot oharaoter1z1llB san1\&r7

m11k, undertook to apec1ty the oondit10ns under Wh10h 1t

uhould be produoed, they were contronted with almost total

laok ot detD.ll information upon thi8 subJeot."

PRESEIT STUDf

The m1lk Qnd cream seleoted tor this investi­

gaUon was brought into the V. P. I. Creame17 trom the

college herd and trom dairy farmers ln the vlo1n1ty ot

Blacksburg. The V. P. I. Creamery was ohcsen for th1s

work, because to our l!llnds it represents an aTerag. Ull­

to-date plant. The output ls not as sreat as that ot

larse plants, nor is the output 80 small a. to exolude

p1p1ng and other nooessary mnoh1ne17 not tound in small

plants. In order for this survey to represent averaSe

oondit1ons eV817 etfort was mede on the part ot the

~uthDr to oollect the samples when normal praotices wore

betns tollowed. All wcrkers in the plant wen not aware

that any attempt was being made to oheck the 8~1tar,v

quality ot their work. Sa~ples were oOllected at

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random. so QS not to arouoe their attention and oause

them to take unusual san1tar,y preoaut1ons.

~e alm of this etudy is to follow the mllk and

oream trom the time lt arrives on the orenmer,y plattorm

untll it 1s ready for del1ver,y. The survey was dlvided

into four parts and samples were oolleoted throughout

the prooessing at fluld milk. butter. and 10e cream to

determine the amount at oontamination taking place. ~e

oane and bottles used in the ore amery were studied to

find the number ot baoteria lett in these utens1ls atter

being sterilized. The cond1tions were entirely d1fferent

tor the d1fferent produots to be prooessed. However.

the Same type of ster1lizat10n. pasteurizat10n. and 0001-

1ng were employed throughout the plant. ~e 40 quart cans

were used exolusively and were always washed and steamed

before sand1ng to the farms.

PAllT 1. DETERI!INIJIG TID: In'LUEIiCE OF THE IllIX CANS

AND BOTTLES 011 THE BACTERIAL COI'lTEliT

Method of Cleaning the Cans. The oans used 1n

this study were waShed in a large vat. containing 60

gallons of a one per cent solution of washing powder.

Eaoh can was sorubbed thol'Oughly wi th a bruah. to de­

flocculate and remove ~ tilth olinging to the can.

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UBuall~ 25 to 35 oans ware washed 1n the S8me vat ot

wash water. Immediatel~ tollowing the washing operation

the oana were inverted over a stenm Jet tor a period ot

ten seoonda to one-halt minuts. There was aome variation

regording the time thot eaoh can was steamed. The period

ot aotual steaming "as oheoked on eaoh can unknown to the

operator ot the apparatus. As soon aB the oans were

sterilized they were stood upright with the lids partly on

so as to taollitate rapid drying. All cans used 1n this

DaIry are ot the 40- quart size.

Oounting the !lumber ot Baoteria, The method

used to determine the number ot baoter1a oonsisted 1n

pouring one llter of sterile water into eaoh oan and shak­

ing thoro1l8hly. An aliquot portion of this 'Yater was taken

to tind the number of baoteria. The plate method vias used

tor counting the number ot baotorla in theDe samples.

Sinoe the oount was al ,yays rolatively low 1t was seldom

neoessary to make more than two d1lutions tor Baoh sample.

The prooedure ueed in counting these sampleo followed the

method outlined by the Amerioan Publio Health Assooiation

tor milk analysls.

Results Obta1ned, In th1s study 31 oans were

used to determine the .ftloienoy ot sterilization. When

oans W&re washed and steamed the lowest oount WI>S , and

the higheat oount was 5,455 bacteria per cubio centlmeter.

I41lk handled in theee oans would be artsoted ve~ 11 tUe,

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sinoe the milk poured in tho oans would usually be above

6,000 baoteria per 00.

The highest number of bacteria per oubic oenti­

meter of wash water was 3,693,000 and the lowest was

1,040,000. Suoh high oounts are due to the faot tha t a

small amount of milk rema1ned in the aan after pouring and

was mixed with the wash water on oleaning.

As 1ndioated 1n Table 1, the oane that were steamed

for 12 seaonds only oonta1ned higher numbers of baoteria

than those steamed for 20 to 25 seoonds. 'rile un.tonmed

oans always had a baoterial count greater than 30,000

baater1a per aublo oentimeter.

• 'Number , Treatment of Cans t])er 00. of , d trinse water' , , , 1 , Cans washed and steamed 12 seconds ,

r 5,025 ,

2 " " • n n n 4, 100 , 3 n " n " " .. 3,420 , I , 4 .. n " .. .. " 5,4~5

, ,- , , 5 .. .. " " n .. 5.178 , , , ,

6 , .. " .. " n .. , 2,810 , , , , I , 7 , , .. " " .. .. , 4,365 , , , , , , 8 " " n " " " 3,600 , , , ,

9 , " " " .. n " 5,400 ,

10 , " " " n .. " 5.360 ,

, , 11 ,

" .. " " .. " 1,900 ,

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Table 1 (oont'd) t , 'No.of bact.' • Can ' ~reatment of Cans 'per 00. ot ' 'NUmber' 'rinse wAtwr' .~~~~,r--------------------------------------yt~~~~~~. , 12 'Cans washed and steamed 12 seoonds' 2,100 • • --~~--f~~~~~~~~~~~~~~~~~~~-Yf--~~~----'

t 13 'n " :t " " If '4.320 ' '--~~-~'--~----------~----~----~--~----T-~~~----

14 n n u " " '" 210' '--~~--fr--------------------------------------Yf----~~----, 15 • Oans washod and steamed 17 aeoonds' 3BO '--~~--~~~~~~~~~~~~~~~~~~~-Tf----~~----'

t 16 ." n T'I It tt n , 400 ' .--~~--,r--------------------------------------Yf----~~----t 1'1 ." " n " 11 " , 100 ' '--~----fr--------------------------------------Yf----~~---- . , 18 t" II n " n n , 50 .--~~--r-------------------------------------~,----~~----, '19 11 If " " n n , 210 ' .--~~--,r--------------------------------------Y,----~~----• 20 'Cans washed and steamed 20 seconde ' 15 ' '--~~--f~~~~~~~~~~~~~~~~~~~-Yf----~~----'

'21.1t n " n n .. '00 • . --~---r------~----~----~----~--~---Tf----~~--'22'" n" n n 1f' 10 t '--~~ __ fr--------------------------------------r,----~~----r, t 23 t If II n tin" , 12 ' , , , -, , 24 '11 " " 11 " " , 30 t --~---Yf----------~--------------~--------r---~~----,

, t 25 ' n n " " , " " , •

14 ' , '26 " " n " "" 8' '--~~ __ fr--------------------------------------Yf------~----, 27 'Cans washed and steamed 25 seoonds ' 16 ' '--~--__ f~~~~~~~~~~~~~~~~~~~-r,----~~----, ' 28 'n n nit" n t 4 ' .--~~--r--------------------------------------'f------~---- ' t ~ a9 " n " n nil, 10 ' ,-"~~--r'--------------------------------------~f----~~----' • 30 ' n " " " " II , 5 1 ,--~~--r'--------------------------------------~'------------ ' ' 31 'n " n n " " • 7 '

It all the baoteria removed tram the 31 ten-gallon

oans , listed in table one wore added t o 310 gallons ot

m1lk (the total oapaoity of the OlaIlS), its baoterial

oontent would be 1noreased by 45 baoter1a per aubio

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oentillleter.

An examin .. t10n 01: table 1 shows that ne .. rly

ever,y ... n had a d1fferent bacter1al oontent. The cloBer

oorrelation ex1sted between those oane whioh were steamed

for twenty seoonds or more. When oans were steamed leB8

than twenty aeoonds the number 01: baoteria .... s always

higher than those cans ste .. mcd more tba.n twenty seconds,

except for one oan.

Method ~ Cleaning Bottles

fhe bottlee are washed with a small brush type

machine. !he rotar,y bruah is driven by ste .... and is

maunted about 18 inohes above the tank in wbioh tbe

bottles are Boaked. Thin wasbing vat contains about

twenty gallons 01: a one per oent solut10n 01: washing

powders. Wben tbe dirt or 1:iltb was completely removed

from the bottles they were inverted in a bottle raok and

placed over a water jet, to 1:aoi11tate thorough rinsing.

As soon ae the r1ns1ng operat10n was oompleted the aame

bottles were l!Ubject to a high pressure of steam, While

in the same posi t10n. The bottles were then racked and

allowed to stand 16 bours before being filled w1th m1lk.

fhe quart bottlos uBed 1n th1s experiment were always

rinsed with 100 co. of sterile water, and an a11quot

port1on at th1B eamplo was analyzed 1:or tbe number 01:

baoteria. fhe prooedure 1s B1m11ar to that used in

-9-

determining the baoterial oontent of the milk oans,

exoept 100 oe. of sterile water is used for rinsing

instead of 1000 oe. When the bottles were re-rinsed the

same amount of rinse water is ueed, and the number of

bacteria are determined by tho method outlined by the

Amerioan Publia Health Asaociation for milk analys1s.

Results 5e.ured: The fol lowing table will serve

to show the baa tori ... l oon ten t of fre OOly washed and

ster1l1zed bottles.

TABLE 2. The Number of ~oteria Found in Milk Bottles whiah have been Sterilized

'Total :No.of' ~~ o:~ (V. 'No.of"Capaolty 'No. cf Mot. removed by 'bottle' of , rinsing wi th 100 co. 'baoteria t tll ,i.rtf'.). , , , bottle , sterile water 'removed t , , 'Ist rrnsl~ '!nd rln.l~ , -, , one , , ,

~ , I , SJ.uart , aD , 9 3,900 , , , , , , , /0

2 , .. , 80 , 20 , 10,000 , , , , , , , , 3 , "

, 105 26 , la,lOO /3 , , I , , , ,,1 , 4 • 15 3 1,800 , , I I , , , ,

~ .. , 12 2 , 1,400 , / , t , , 6 , n 28 , 4 a,200 , 3 , I , ,

' ) ,,-, 7 • 70 , e 1,800 , ,J , , , , , 8 • , llO , 17 , 12,700 ' ,~,j , I , t , , J , 9 u 8 , 2 , 1,000 ,

, , , , • I./-, 10 • , a , 1 • 400 , ' . , t , , 11 , n 16 , 4 • 2.000 ' j . , , t t , , , 12 ,

" , 20 5 .2.500 , :1

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Table 2 (oont'U , 'Capac! ' No. ot' of

'No. or :Baot. removed by ''!otal lo.'~ {'" .­, r1nsing with 100 00. 'bt bao- , "'-" , sterile .ater 'teri& ' -cr;';/' 'bottle' bottle , , '1st rliis1ll8 ; 2nd rinelng 'removed ' .

, lone' , (I. , 13 ' pint' 12 ' 4. '1,600' . n '-='-,'-I.::='-.. '---==----r' ---"----,,_"="""''''''"-, , '14." 19' ~ 2,400' ?,' I , , 1 ,

, 15'" '3'1 10' 4., '100 ' '1, ') ,-=:......,,----.. ,--~~--r'-~~---,,_~~""'"---, : __ ~1~6~,,--.--.. :----1~0~---T:--~2~---'r-~1~,~2~0~O~ __ ' I '1'1" l4. 3' 1,'100 , 1,/ ,-~-,-----~--~---r,---~----,,_..=..~""'"-,

:_~1~e~,:----"--.. ,----__ ~9--_r:---~1:----,r_~1~,~0~0~O~ __ , : I 19 '" 11' 2 1,300' I

,-~:......,-----T'---==-----r_-~=------,,_..=..""''''''"---,

'20" , 9 ' 0 '900 ,-~:......,,----.. ,----~--r_-~=-----,r_-~~---,

t 21 tnt 2 to' 200 ' ,-~:......,,-----;---=---r'--~---,,_-~~-f 22 " , 0 tOt 0 t ,--~:......,-----~--~---r,--~---r_--~---

q , ,

r 23 tn, 8 • 4, 1,200' I . • -=:......,,----.. ,---=---r'--~---,r_~~~---, ,j

'24 " , 4. '1 600' ,-=:......,-----~---~----r,--~---,,_-~""'"---, , ' __ !:!.2~1l~_'_~. ___ ' ___ 2~3~ ___ ' ___ ~3=__ ___ '~..!2"'.~6~OO~_' "J

In table 2 we tind that the greatest number ot

baoteria per oubio oentimeter was 110 and the loweet

number .&s O. In every oase the seoond rinse water waa

lowor than tho tirst. On the average. the number ot

baoteria touud in the milk bottlee waa higher than the

numbor ot baoteria tOlllld in the 40-quart m1lk cans. If

both oans and bottles were tilled with milk ot the same

baoterinl content, it would be found that the number ot

baoteria per co. ot milk would be higher in the case ot

the bottles.

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PART II. DEl:ER!.IINIl'IG l:HE SOUIl.CE OF BACTERIA AIiD

THE METHOD OF CONTAMINATION DURING

THE PROCESSING OF FLUID MILK

Tho market milk at the V. 1'. 1. CrellJltery is

prooesaed by two di~terent methods.

~he milk going out on t he route is produced by

the 0011ege herd and hereatter designated as m1lk nAn,

A8 Boon .. a th1s milk arrived at the ore amery it was taken

to the seoond ~loor by an elevator and poured d1reotly

into the pasteurizer, Atter pasteur1zat1on the milk 1s

piped t o the cooler and from there into t he bottling

maoh1ne,

Part o~ the milk used by the dining hall was

brought to the creamory by farmers trom the vioinity ot

Bla oksburg, and will be known hereafter as milk nBn.

This milk was poured into the reoeiving vat and pumped

to the seoond t loor, into a large holding vat. From

there the milk was pumped through a heater and tilter

into the past eurizer. Atter pasteurization, the milk

was allowed to run over the oooler and then poured into

ten-gallon milk cans which had been thoroughly sterilized,

Colleoting Samples: All samples were colleoted

in sterile, 60 00. bottles, whioh were stoppered end

immediately plaoed in the anti-hardening room, whioh had

a temperature ot 32 degrees ~hrenheit. The samples were

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kept at this temperature until they were ready to be

tested for the number of bacteria.

Kethod of Counting Baoteria: In this experiment

eaoh sample of milk woo tested for the number of baoteria.

as far a8 possible. by three methods of baoterial analysis:

the plate oount. the miorosoopio oount. anA the methylene

blUe reduotion test. The plate oount was found to be the

most dependable. sinoe it was the only teet that oould be

used during the entire survey. It waR not praotical to

use the mioroscopio oount after pasteurization. aa the

dead organism would bs revealed as well as the aotive

ones. The methylene blue reduction test was not a8

aoourate for testing milk &fter it had passed Over the

cooler. because the peroentage of dissolved oxygen was

appreciably inoreased.

The plats oount was made aocording to the

direotions outlined by the A. P. H. A. for the analysis

of milk. Dilutions of 1-100 and 1-1000 were used and

plated out on nutrient agar. All plates .ere inoubated

at 37 degrees Oentigrade for 48 hours.

In setting up the methylene blue reduotion

test. ten oubic csntimeters of m1lk were added to a

sterile test tube oontaining 1 00. of a 1-20,000 solution

of methylene blue. ~le tubes were 1noubated in a water

bath at a temperature of ~7 degrees Centigrade until

reduoticn took place.

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~e microsoopl0 count was carrled Qut a ecord­

ing to the d1reotiona given 1n techn1cal bulletin number

49 of the Geneva, N. Y. , Exporiment Station.

Processing .2! ~ ~ ':he f1rst 88111ple was ttlkcn {,fter the mill<: was

thoroughly mixed in the rece1ving vnt. It was not praoti­

oal to take .. oamp10 of milk :Crom sach oan b"fore empt;y-

1ne;. since the quantity I.!.rld qual1ty of the milk in <lMh 01Ul

Was quits variable. From t he z'eo e1 v1ne; vat the m1lk was

pumped to the seoond floor b;y a. p1ston typo pump where 1t

emptied lnto a large, gla.ss-llned hold1ne; va.t. ~. second

sample was colleoted as the milk entered the hold1ng va.t.

<rho lang'th of tlme that the milk remUned 1n the holding

vat vari .. d from tive minutes to ono hour. Ilhen the milk

was Z'Oaay to be pumped further. a thlrd 9 .. m1'le was oolleot­

ed in the va t, after thorough mixlng with nn eleotrio

aglt..'l.tor. ll.Y the USG of a Slllall oentrifUgal JIUI!IP the .. 1lk

waB then forced through the heater and filter, into the

pasteurlzer. The fourth sample WM ttlken as the milk

entered the pasteur1zer. From the holdine; vat to the

pasteurizer th.G mill: Was kept 1n p1pes and never exposed

to the &ir. <rhe last operation increased the tfllllperatUJ.'e

of the milk on an average of 34 degrees ~enheit.

~e fifth sample wae ~~en when the pasteurlzer

",as tull. 'the coll 1n the pasteurizer "as 9t!U'ted before

-14-

collecting the sample, GO that the milk would be

thoroughly mixed. The milk was pElsteurlzed by heatina

to a temperature ot 145 degrees Fahrsnheit, and held at

that temperat\ure for twenty m1nutaG. !he selt-reoord1na

thermometer was not uoed every time the mill< wa9 pasteur­

ized. ,\ft. r pasteurization , while the milk was st1ll hot,

it Vlao allowed to run OVOl' the oooler by gran ty. ~

oooler oon&1oted of two sectlons, whioh were intended tor

water and brine. llu.r1na th1s su.-vey, wr.ter was th .. only

cooling modium. 'Zh. milk was oooled down to " temperature

of about 65 degrees Fahrenhe1t; this temperature fluotuated

due to t he size ot the tilm of mUk pas91t1/l OTer the

0001:8r. From the oooler the m1lk w .. e .. Uowed to flow into

ten-gal lon cans, wh10h had been thoroughly sterilized.

Xhe milk was then rendy to be deliverod to tho d1ning hall.

Olesn1l1;6 Utensils: Atter each day 's run, the

piping and maohinory was first rinsed with oold water and

then with bolling hot "ater . Every part ot tho equipment

wa.s tnorouenly sorubbed with a brush, USing h1gh grade

washing powders . ~o piping was "lwaye dissembled so as

not to a llow any sodiment to collect in the crevioes where

the pipes were fas tened together. After scouring, the

pipes and maoh1nery were again r1nsed with boil1ng water.

All ot tho piping wan t horoughly steaMed, then allowed to

drai n over night, and assembled Just pr10r to using.

-15-

.!l!!lIUlts of stucl,y:: This part of the wrvoy con­

sisted in following seven batches of milk from the time

it was poured into the receiving vat until it was ready

to be delivered. Eight sample . were collected at regular

interval. during the process ; making a total of 56 samples

for this part of the survey.

The following tables will servo to indioate ths

bacterial ohanges which took plaoe during the various

operation. in the processing .

-16-

TABLE 3. In:fluonce of Processin~ Karket Milk on the llacterial content , , , 'Mieroscopio , lte thy1ene I

I I Plate Count oount I Blue ned. I

'So.mple' Place where samples were I No. 0'1 i Inorease in T 01 t eat I No. I taken tbaot. per 'bact. per I lIo. of I Hours: I

'oc. milk co. milk , Bacteria , loIinu teo , , , I I , , • I

I 8 00 I

1 C , Samll1e taken in ho1din~ tank ' 30,794 7,782 I 850,000 I 7:30 I , Sample taken after going thru' , , I

1 D I he .. ter and tilter I 41,451 10,637 I 1,080,000 I 7:00 I

Sample taken in pasteurizer 1 , ,. 1 I

I 1 E I when 1/3 full I 47,750 I 6,319 , 1,100,000 , 5:15 I

1 Sample taken in pas teu;roizer • I

1 F I when :full 84,300 36,550 I 1,226,000 2:05 I

I 1 1 1 • I

1 G I Sample ta...lcen atte{ , 18,167 - 66,113 9:00 I l!B.S eurlzatlon

I • 1 I , I

1 H , Sample taken af'ter cooling 22 ,512 4,325 9:00 I

I 1 , I

1 I I Sample taken in cans :n,634 I 9,122 I 9 :00 I

TAllLE 4. Influence ot Frooesalns »arket Kirk on the llacterial Content 1 1 t o ' lletliYlene I

'Sample' Place where sample was Plat. Count '.10r0800p10 ' Blue Red. I

, No. , taken '110. llaot. 1 Increase I count test I

I 1 I · , 2 A. , Sample taken in emp!;in~ T~t

, 81,820 1 310,500 I 4:00 I

1 , ,~

$ample tciken from p pe ea-I II B I i118 into holding tank 87,675 5,855 540,000 I 2:00 I

,- " ,

2 0 I SamEl. taken in hOld1n~ tank I 135,700 46,025 690,000 1:45 I , Sample taken after g01ng thru l F' , I 2 D I heater and filter I 220,500 I 64,600

, 1,050,700 , 1:20 I

I Sample taken In pasteurizer ,

I 2 E , when full I 227,805 7 ,305 I 1,175,000 I 1.15 I

I 1 Sample t8lten atter 1 1 , I 2 F , pasteurization I 7,600 , - 220,205 I 8:30

t I

, , 2 G I Sample taken after oooUng 10,240 , 2,640 I 7:45 I

I t , , t

2 H I Saml11e taken in .ans I 12,725 I 2,485 I 7:45 I

TAllLE 5. i T , , ' Sample' , No. '

-17-

Influence of ProceBs1ng Market M11k on the Baoter1al Content

Plaoe where so.m:ple taken

Vias

, , , I ,

,_-!o3c.!'A,',s~"~m!!:p"l~e~t~"{ik~.~n-{1n~e~m!!::p~tY~1n~g~v~a~t-;..' _..;3£....;, 2!C0~0,,-....;.. ______ ,~.-,9~0~0!J!,-,0';.0,,0c---;'_-,5~'.!!4~5~_'. , Sample taken from pipe Iead- ,

3 ll' ins to hold1ng tank 6 ,125 2,925 '1,095, 000 _.-_.:4":,,4,,,0,--_' • , , , I

'_~3~C~'~S;a~m~p~l;e-rt~ak~en=-~ln7.h~O~1=d=i~ng~=t~"~nk~-r'~1~4~,1~7~0~-r_~8~,~0~4~5~_~'2~,~4~0~Ow''-'0~0~0~_~'_~3~:~3~0~_' f sample taken after goIng' , , f

, 3 D ' thro11g~hcater and fnter 36 , 490 22,320 '2,700 ,000 ' 2:30 ' ,--~~-r-s~am==~p~l~e~~~ak~e~n~i~n~pa~~.~t~eur~~i~z~.~r~~'~~~~~~'-~~~~-~'~·~~~~--~-~~~--when full 43 , 525 I 7,035 '3,100,000 ' _-,2,,-:,-,0,~0,--_'

, Sa mple taken after ' f -,--3 E

:3 F ' paateur1~atl o!l.f 12,250 f_ 31,275 ' 9:15 ,--~~-,r----------~~~~~~~~~,r-~~~~-'--~~~~--~- ,r---~~--

'_~3~G~'~S~a~m~p~l~e~ta~.~k~e~n~a=f~t~e=r.:c~o~ol==ing~_-r~1=7~,3~0~0~-r' _ _____ T' ______ .~r-~8~:~30~ __ ' , , r , 0;3 H ' Sample te.ken 1n cans 19,150 1,850 ' ______ ' _-"'-8,:.:"'1"'5 __ '

TABLE 6 . I nf"luence of Prc cessi n~ Market Milk on t he Bacterial content , , , .., ' lLe thylene ' Sam.:pl e ' Place where sample waG , Pl a. t . Count tilicrOBoopic , Blue Red. , No. • taken 'No. 1laa~.

, Increase • oount teat • , 4 A , Sam~le t aken 1n emRtl1~ vat , 67,575 320, 000 3:50 • , Sam:ple t aken trom pipe es.a:- , ,- , , 4 B • ing to holding tank , 122,970 55, 395 , 495 ,800 • 2: 45 , , , , 4 C , SamEl. taken 1n holdinjl tank ' 105,850 ,- 17,120 503,700 2:30 , , , Sample taken aft er going thru' ! , • 4 D , heater and f11ter , 131,850 26,000 51B,605 2 : 15 , , , Sample taken in pasteuri zer , , , , 4 ]I , when full , 134,950 3,055 650,500 2 : 15 , , Sample taken after , , , 4 F , pasteurization , 1,180 '-133,725 • 10:30 , , I , , , , 4 G , Sample taken after ooo11ng , 10,550 , 9,370 , 10:00 , , , , , , 4 H • Sam,l!le taken in oans 11 , 100 550 , 10: 00

-18-

'rAllLE 7, Intluanoe of Processing IIM'ket lI11k on the Baoterial Content I I . ''}(icro seopio I Iietlij'lene , , 'plate Count , oount , Blue Red . ,

• Sample' Place where sample was , lio. at 'Inorease in ,. hat , , Ho. t taken 'baot . per 'baot. per I No. of • HourB: , t '00. milk ,

00. mil}: Bacteria , 1I1nutes t I I I ,

t 240

, , 4 , t 5 C t Sam;2le taken in holdln5 tank , 62,680 19,350

, 330,400 , 3:30 t

I Sample taken after going I

5 D • through heater and fl1 tor 106,060 43,380 440.000 2:30 t Sample taken in pasteurizer I I , I , 5 E t when !'ull 116 ,000 , 9.940 t 480.000 , 2:00 t

1

t 6 F t Saml1le taken after pasteur'n , 1,275 t -114.725 , 8:45 t

t t 5 G t Sample taken :l.:fter cooling 6.200 t 4 .925 t 7: 50 t

t 5 i! t Sam;21e taken in cans 6 .800 t 2.600 , , 7:40 t

,

TABLE 8. Influence of Processing Karket 1I1lk on the :Baoterial Content I 1 I l.leth.,:rone t

Place oumple was 0 t Blue Red, t

, 6 A , Sam le taken in em 10 320 , , 2 400 000 6 :40 ,

, Samp e en rom p pe ea -6 11 , i~ to hOldln~ tank t 13.740 , 3,420

, 2,520.000 6:10 • , 1 , , sampe taken af er going • 2.640.000 5:00 , , 6 C , thro~h heater and filter • 25.260 , 9.510 , I

, , t Sample ikon in pasteurIzer

3,000,000 4:15 , 6 D , when !'u11 36,150 , 12.900

, , , Sample tBJien lifter 1 , , , , , 6 E , ;2asteurlzatlon , 15.725 , - 20.325

, 8:00 1 , , , t

, 6 F , Sam;21e taken after cooling 22,200 , 6.475 , 7:30 , , ,

6 Q , Saml!le taken in oans 32.075 , 9.875 , , 7:20 ,

TABLE 9 . Influenoe of Processing Karke t Milk on the Bacterial Content I I I , l!eth;ylene • I I , Plate Count 'llicro s copi0 , Blue Red. , 'Sample' Plaae where samples were , io. of I Inorease in' count , test • , No. I taken 'baot. per ' baot . per No. of , Hours : • I ·cc . milk • 00. milk Baoteria' 1I1nutes • I I I • • 7 A I Sam111e taken in em.!!tlln~ vat I 226,000 • • 2,400,000 • 3:45 • • Sample taken from pipeead- I I .

7 B • ing to holding tank • 241,000 15,000 I 2 ,600,000 3:15 I I -. ,

7 C • Sam!1le takan in holdinl> tank • 244.050 2.950 &, 2,800.000 3:15 • I I Sample takon Idhr go l ng I

7 D • thro~h hea ter and filte r 253,000 8,950 • 3,300,000 3:10 Sample aken In pas teurizer I , 7 E when full I 257,700 4,700 • 3,600,000 • 3:00

• I Sample taken after ,

• 7 F • ;2Bsteurlzatlon • 900 - 256,750 10:15 I

• • I

'1 G • Sample taken after aoaling , 1,125 • 175 , 10:10 • t t , '1 11 I Saml!le taken in cans 1, 300 • 1'15 • 10:10 •

-20-

Influenoe of Pumping on the Baoter1al Content:

In every oase durill8 this survey there wss always an 1n­

orease 1n the baoterial content, as a result ot the t1rst

pumping. This inorease was qui te variable; the smallest

inorease in the baoterial content per oub1c centimeter ot

milk WQs 2,925 and the largest inorease was 55,395. Since

this increase seems unusually larGO it ooourred to the

author that a portion ot the increase, as measured by the

plate oount wss due, at least in part, to agi tation and not

altogether to oontamination. A study was made to determine

the etreot of agitation on the number of baoteria, when

measured by the plate oount. Reeul ts of this study will

be found on pages 16 to 19, 1nolusive.

The pump used in th1s experiment was a piston

tn>e pump, dr1ven by !l one-hal! horse power motor.

Colleotive Inf1uonoe of Beater and Filterl In

every oase the filtering and heating operations added

mater1ally to the bo.oteria1 oontent. ~he milk did not

tlow through the heater and filter by gravity, but waD

forced through by a oentritucal pump, whioh probably

ass i sted 1n breBkill8 up olumps and oha1ns of bacter1a.

Also, the heater ra1sed t he temperature of the m1lk to

about lOa degrees Fahrenheit, whioh temperature was more

favorable to bacter1al Srowth. The clean1ng prooedure

is somewhat more difficult w1 th the heater than any other

p1ece of .... oh1nery. Larse films of sediment otten

-:n ...

oolleot on the walls of ths hsater, whioh aot to re­

oontaminste the subsequent lots of Milk. It is thought

that More oontamn&tion takes place during this operat10n

than any other operat1on in ths prooess1ng of milk.

Partial proof for this may be found in table 9 , where the

heater and filter only added 8,950 baoter1a per 00. of

M1lk. ~1s 1mprovement in quality resulted in a thorough

oleaning of ths heater. Sinoe this operat1on always

gave a high inorease in the number of baoteria, the plant

operator was advised to give special attent10n to the

oleaning of the hea tar. llooause of the ohange in

praotioe tho relatively small increase in bacterial oon­

tent, given in table 9, was obtained.

During the prooessing of seven lots of milk,

the greatest increase in baoterisl oontent, due to milk

passing through the heater and filter, was 64,600, and

the smallest inorease was 8,950 baoteria per 00. of milk.

Influence of Pasteurization: There was in each

of ths Beven lot. of Milk ... very Marked deorease 1n ths

bacterial oontent due to pasteurization. ~e efficienoy

of pasteurization varied from 99.6 to 56.2 per oent.

~1s erest variat10n WIlS attributed to the d1fferent

periods for whioh ths milk was held at the pasteurizat10n

teMpera'l:nre. In no Ollse could this increase in be.cter1al

numbers be attributed to thermophylio baoter1a. However,

there 1s a poss1bility that the thermophylio baoteria

-22-

whiCh frequented the milk in this surv.y ..... ri.d al1eht­

ly for the different lata of milk.

~e greatest increase in baoterial content per

oubio oentimeter of milk ooaurred from the time the milk

was poured in the pasteurizer until it was full. Without

a doubt, a. greater part of the increase came from a poor­

er quality of milk whioh passed through the same system

subsequent to the tirst emptying vat full of milk. It

took about four vats ot the milk to till the pasteurizer.

A emall portion of the increase in the number of baoteria

Was due to the growth whioh took plaoe from the time the

first milk entered the pasteurizer until pasteurization

waB atarted.

c Influence of the Cooler' ~e increaae in the

bacterio.l oontent due to the oooler waB reiati vely oon­

sistent, ninoe the same cleaning routine was followed

dally. At no time during the survey was any oooling

medium exoept water used to 0001 the milk. However, the

cooler was 1nstalled with a sect10n oonneoted to a brine

to.nk, but advant888 W,,& never taken of this opportuni t;y

to 0001 the II1lk to a low temperature. Henoe, during

the period of delivery the m1lk w"'s at .. temperature

whloh was favorable to baoterllll growth.

-23-

l'rocessinp E.! !!!.ill ~ The processing 0:1: milk ":Bn d1d not involve aD

many operat1ons as milk "I.", since the milk was poured

directly into the pasteurizer. A reduotion 1n the

proeesaing operations wa.s accompan1ed by a deorease 1n

oontam1nation. ~ this method, it was possible to prooess

a milk with lese contamination beoause the elimination of

extra. machinery resulted in mainta1n1ng a product w1th a

minimum number of baoteria . All milk used 1n thIs prooess

was produoed by the college herd. This milk was bottled

and delivered to .ustomera In the city of :Blaoksburg.

Usually the milk was bottled and ready for del1ve17 within

an hour and a half after the prooessing was started.

Colleotinp Samples, In th1n part of the study

only five samples were taken from Baoh lot of milk to

determine the influence 0:1: the various operations on the

bacter1al content. The first sample was oolleoted im­

mediately after pouring.all of the milk into the past.eur­

her. To 1nsure uniformIty in miXing, the ool1s in the

pasteurizer were allowed to run for several m1nutes

before the sample was taken.

The seaond sample was 00 11eo t~d directl.,. fro ..

the pasteur1zer after heating for thirty minutes. In

oollecting this sample a sterile p1pette was always used.

As soon as the m1lk was allowed to pass over the oooler

the th1rd sample was taken. This is the sams cooler that

-24-

was used 1n oooling the milk proceosed by method "A".

Slnoe mllk "B" was the flret to be prooessed, 1t was

allowed to paS8 over the cooler f1rst.

!he fourth sample was taken from the tank or

the bottle filler w1th a sterile pipette. The m1lk was

thoroughly stlrred to get a uniform d1stribution of

bacterin as well as butterfat, before the sample was

taken. The fifth asnple was taken from quart bottlos

which had been automatically oapped. !hree samples were

taken from eaoh of three bottles and the o.v.roee n1ll!ber

WOoS aooepted as the bacterial oount for the tlrth sampl ••

This was done with the ldea of olim1nat1ng the posslbl11 V

of exoess oontam1natlon due to any one valve on the bottle

t1llor.

Results Obtained: The opportunity for oontami­

nation wo.a brought to a m1nlll1Ull1 when the mllk was pro­

oe.sed by th1s method. The amount of equ1pment was very

small and only about f1fteen feet of p1p1ll5 was used in

oarrying the m1lk from the paoteUItzer to the bottling

mach1ne.

!his part of the survey oonsisted in oolleoting

samples on five lots of milk. F1ve samples were taken

at various intervals from the time the milk W&B poured in

tho pasteurizer unt1l it was bOttled and ready for deliver,y.

All ohanges which took plaoe during the various

stops will be given in the follow1ng tables.

-25-

TAllLE 10. In1'luence of the Various 0R"rations on the Bacterial content , , , I- , lletliYlene • I I Plate Count 'Mioroscopio • Blue Red.' 'Sample' Place where sample was 'E'o. of , Inorease In I count • test I

• No. I taken 'b~ot. per 'no. of Baet . No. oi' • Hours: , 'oc. milk I Bacteri .. • lIinutes • , I

, • I 8 A • Sample taken in pasteurizer I I I •

when full ~,850 • 890,000 • 8:45 • , 8 B I Sampl. taken after • , •

pe.eteruiza. t10n 1,110 • - 4,740 , 8:35 •

I I i · I , 8 C I Sample taken after cooling 6 , 740 • 5.630 • • 7:50 • • , • ,-- I I· I I

8 D I Sample tak;,n in bottl1ng 8,395 I 1,655 I 7:10 • I • machine I • • I

i t i • I 8 E ' Sample taken in bottles 10,105 1,710 • I 6:15 • , • •

TABLE 11. Influenoe of the Various 0I!eratlons on the Bacterial Content I I , I , Uethylsne • 'Sa.mple' Plao e wile.("8 sample was I Plate Count , l1icroscopio' Blue Red. , , No. I to.ken '10 . Baai. I Increase • oount , test •

I , , , • 9 A • S .... ple to.ken in past~nrizer , I •

when full , 5,800 180,000 • 6:15 • • i I , I 9 II , Sample to.ken after , • • , pasteurization 2~0 • - 5,550 • • 9:25 •

I I , • I 9 C I Sample to.ken after aooling , 1,725 1,475 • , 9 : 15 • I , I • I 9 D , Sample taken in bottling • • • • I I maahine 8.770 • 7,045 • • 9:15 I

• , I , , I

9 E I Sample to.k.n in quart I • I • bottleo 9,100 I 330 I • 9:00 •

-26-

TAllr,>: 12, Influenoe of the Various _QR,vat lons on, the Bacterial Content , , I , Methylene • • • • Plate count 'U1oroscopio • Blue Bed. • • SSIllple ' PIa.e where sample 1,'(8,5 'Ro. of , Increase in • oount • test • • 110. • tal<en 'ba.ct .. per' no. of Baot. T No. ot • Hours. -. ,

'O Ct milk' • Ba.terla • Minutes • • I f f , • - t

• 10 A • Sample taken in pastaurlztlr • • • • • when :f'U.ll 9,110 • • 2.150,000 • 6,45 • • , , , , • • 10 B • Sample taken after • • • • • • pasteurizat10n • 250 • - 8.905 • • 6,20 • • , , , , s , • 10 C • Sample taken !lner coolin{; • 9,2'00 • 9,095 • 6:20 • • • • • • • • • , , • 10 II • Sample taken in bottling • • • • • maohine • 28.150 , 18.850 • • 6:00 • • i , , , , • 10 E • Samp1 e taken in quart • • •

bottles • 31.200 • 3.050 • • 5:15 • .'II!

TABLE 13. Influenoe of the Various O}!sratlons on the l3aoter1al Content , , , "

, lIetby1ene • 'Sample ' Place where sample waS Plate Count • l!icroaoopio • Blue Red. • • no. • taken 'No.Eact. 1 increa.se , oount • tost • • , , we , • • 11A • Sample taken 1n pasteurizer • • • • • when :f'U.ll • 5.850 • 890,000 • 8.45 • • • f , , • • 11B • Sample taken after • • 6:55 • • ~a.ateul·lzatlon • 1.110 • - 4.740 • • • • , , I , • • 11 C I Sample taksn after cooling • 6,740 I 5,630 • • 7:50 • • • • I • • • ,- I , T , I 11 D • Sample taken in bottling • I • I 7:10 I

I • maohine • 8,Z95 I 1.655 • • • • , I I I-I 11E I Sample taken in quart • 10,105 I 1,710 • • 6:15 • • • bottles I • •

TABLE 14. Influenoe of the Various 0l1erations on the Bacterial Content , , , , lIethylene , , Plate Count , , , 'lUorosoopio

, Blue !led. , 'Sampl e ' Plao e where sample was ' No. ot , Increase In f count , test , I No. I taken tbaot. per' no. o~ Baot . ' 'Bo. of , Hburs: , ,

l OC o milk , , Bacteria. , )(1nut.s , , I , , I , I 12 A I Sample taken i n pa.steuri z er , 34,500 , , 210,000 I 5:40

, I when full I I I

I , , , • , , I 12 B I Sample t&kon .u:tor I 17~ I 34,325 I I 9:00 I -, , I I • I

I , , .- , , I

I 12 C I Sample taken after cooling 5 ,260 • 5, 085 I , 9 :00 ,

, , I , , I , , , , 12 J)

, Sample taken in bottl1ng I I I I ,

, I machine I 7,570 , 2,310 I , 9 :00 , , I , I

I 12 E Sa.mple taken in Q.ucrt I ,

I I bottles I 7,800 , 230 I • 9 : 00 I

-28-

Influence of the Pasteuri zero l!y stu4ing the

fieure. presented 1n tables 10 to 14, it io found thst 1n

ev.r~ oaS8 the b~oterlal content was oon81derabl~ reduoed

by pasteurization. This pasteur1zer was not equipped

w1th a solf-reoording, dial thermometer, and the tempera­

ture was oontrolled by olose obaervation, using a f loat­

ing type thermometer. After pasteur1zation, the m11k Was

never allowed to 0001 down, but passed over the oooler

immediately. In the five lots of milk the highest number

of baoteria whioh esoaped pasteur1zation waS 1,110 and the

lOllest WaS 115 baoter1a per cc. of mUk. l1sually the

poorest qua11ty of raw m1lk showed the most complete

destruot1on of baoterial growth, dur1ng the heating

process.

Influenoe of Cooler: The milk started over

the oooler at a temperature ot 140 degrees Fahrenheit

and was oooled to about &5 degrees Fahrenheit before

being bottled. In every caSe the oooler inoreased the

baoter1al oontent. The greatest increaoe was 9,095 and

the smallest inorease was 1,100 baoter1a per QQ. ot

milk. It is thought the t B small portion of the 1norease

oQllle from the atmosphere in whioh the oooler waa operat­

ing.

Influenoe of the Bottle Filler: The bottle

filler used in the plant was of the rotary type and

-29-

and oould be ad~usted for ~ s1ze bottles. It oons1st­

ed of " tank and s1x valves, eaoh valve hav1ng " stem, a

sleeve, an a1r tube, a w1re ooil spr1ng, and a rubber

WAsher.

The tank and all parts were scrubbed thorough~

w1th a brush and washing powders (tri-sod1um phosphate),

then rinsed with a hose. The bottle f1ller Was not

steamed but was always washed with boiling hot water §nd

allowed to stand sixteen hours before use.

There was always a slight oontribution of

baoteria due to contamination in the bottle f1ller. It

1s believed that the greatest oontam1nat1 on took place in

the valves since they were the hardest to clean, and are

more likel y to oollect filth. The l argest number of

baoteria added to the milk by the bottle filler, in ~

case, was 18,850 and the smallest number of bacter1a Was

1,655 per co. of milk.

Collective Influenoe of the Utensils: The milk

was prooessed, bottled and ready tor delivery w1thin two

and a half hours after 1 t vtas bro'llght to the oreame17,

in the raw state.

In table 9 1t will be noted that the baoterial

oontamination "as much reduced. Th1s improvement is a

result of a thorough oleaning of all utensils, whioh waa

followed by a thorough steaming of all utensils where

t easible . These results show that when the utensils

-30-

are thoroU8h~ oleaned, milk of high qual1 ty oan be

llroduoed wi t1~1ftiOUlty • Atter making a oomprehensive study ot the results

ot this experiment, it was found that the oolleotive in­

fluenoe ot the heater and tilter are the greatest souroe

ot oontlllllination in the plant. The increase in the

number of baoteria during this oll"ration is probab~ due

to a breaking up ot the olumps ot baoteria and a lso the

tostering of bacterial growth, by a favorable temperature.

Eftect ~ Agitation

There was always a distinot inorease in the

baoterial content of milk from the time it lett the

weighing vat unt1l it reached the llasteurizer. An effort

to find this variation resulted in an inspeotion of the

various operations. It is thoU8ht that this increase 1s

not entirely due to oontamination but rather it 1s due to

a breaking up ot the clumps ot bacteria. The segregation

ot suoh olumps give riss to smaller olumps, each cf whioh

llroduoe a colony on the agar plate.

Wi th this thought in mind an investigation was

made to see it a ratio could be found whereby it would

give the degree ot breaking up ot bacteria whioh ullU&lly

frequent market milk. This ratio was asoertained bl

oomparing shaken and unshaken s8l!lples ot milk.

The plan ot allproaoh to determine the etteot

-31-

of agitation oonsisted in taking a sam»le of market milk

»roduoed in the nomal way, and pouring 35 00, of this

sam»le into a dilution bottle. ~s sam»le of milk was

then plated out atter sha.king a def1n1 t. number of strokes.

Raoh stroke consisted in shaking the milk back and forth,

thro1lgh .. d18tanoe of eighteen inches. Atter each interaml

of shaking, one 00, of the milk waa »ipettod into a

diluticn bottle oontaining 99 00, of sterile water, thus

making t\ 1-100 dilution, 'rhe dllution bottles were alw~s

shaken the same number of strokes as the original one 00,

of milk was shaken. Each dilution resulting trom a

def1ni w number of strokes WBS plated out in triplioate to

tind the number ot oolonies per 00. of mill:.

The number of oolon1es developing from four

slllll»les of milk, with inoreasing amounts ot e.gi taU on,

are listed in tables 15 to 18, in~lusive,

R •• ul ts Secured:

1'Al!LE 15. Effeot

-32-

of Agitation on the Bacterial Content of lUll: ,

Amount of Shaking , PLAU coUll''r' Ch""6e In • 'No. of baot.' Baot. • 'per co. of 'Content '

.~~ __ -= _______________________ :r-~m~i~ll:~ ____ ~'~ ________ .. :

• Ciroular motion to d18- • • • ___ t~r~1~bu~t~e~o~lum~p~s~un~i~f~0~rm~1~Y __ r-~~~~ __ r-_________ '. · , • ~S~1x~~s~t~r~O~k~e~s~~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~' __ -:~~~ __ ~~~~~ __ ," , '.~T~.~n~s~t~r~O~k~e~·~~·~·~·~·~·~·~·~·~·~·~·~·~·~·~·T' __ ~~~~ __ ~~~~~ __ :

:.~r~o~u~r~t~e~e~n~s~t~ro~k~e~s~.~.~.~.~.~.~.~.~.~.~.~, __ -:!L~~ __ ~~~~~ __ :

:,-=E~i~g~h~t~e~e~n~s~t~ro~k~e~s~.~.~.~.~.~.~.~.~.~.~._. __ ~~~~ __ ~~ __ ~~ __ :

• Por o.nt inoreaee due to agitation ••••• 2~ • • • •

TABLE 16. Effeot of Agitat10n on the Baoterial Content of Ifill: ,

• • AIIloun t of Shaking

CliiiiiBe in • Baot. '

Content •

, PLAiJ'l! COthlT' 'No. or bact. f

'per 00, of t

:;==c=====~=c====~*D========a?ia=~Jmi1~f~. k'===·F=========oa t Ciroular motion to f , t

:, ______ ~d~1~D~t~r;i~b~u~t~e~c~1~um~p~e ______ ~--9~6~14~50~---r:-----------:

,~~~~~~~~~~~~~r_=1=12~1~2~OO~--r:~~~1~3LI7~~~O~·

,-=~~~~~~~~~~~~r_=1=19~1~7~6~O~~·~~~~7LI5~6~O~·

·_;F~o~ur~t~e~on~~.~t~ro~k~.~B~.~.~.~.~.~.~.~.~.~.~._· __ l:2~5~.1:5~O~ __ '~+~~5~lc3~9~O~· • •

• Six .trokes ... ... .......... ' I , • Ten 8trokes • •••••••••••••••• I

• Per oent increase due to ag1tation ••••• 2?~ • '===-==---==========-=====================-

TABLE 17.

-33-

Effeot ot Agit~t10n on the Baoterial Content of ]ulle

Chillie In ' Bact . I

Content '

'Circular motion to distribute'

'-"F1~v~e~u~t~r~o~k~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.,'---=~~~ __ ,--L+~6~9~0 ____ ' ,- , , Ten strokeo 4 • • • ••• ••••• •• • • I '" 370 ,,-"~~~~~~~~~~~~~~, __ _=~~~ __ ~-I~~ ____ ,

',-=F~i~t~t~e~en~e~t~ro~k~e~8~.;.;. ~.~.~.~ • • ~.~.~.~.,' ___ =~~~-, __ ~+~8~50~ ___ :

'~fw~e~n~t~y~8~~~r~o~k~.~S~.~.~.~.~.~.~.~.~.~.~.~.~.,-__ ~~~ __ ~ __ ~+-:3~50=-___ ,- , t

, Thirty strokes • .• •• .. •.•••• + 390 , '-"F~i~t~t~1~8~t~ro~k~.~s~.~.~.~.~.~.~.~.~.~.~.~.~.~._' __ ~~==~ __ ,-~--=5~70=-___ ' ,- , , , Per cent incre~se due to ag1tation •••.• 2~ , ,

~AllLE 18. Efteot ot Ag1 tatlon on the Baoterl .. l Content ot )f1lk

! ' PLKT~ COUNT' , Amount at ShakilOg , lIo.o! baot.' , 1 :pc r 00. of '

Change In ' Baot. '

Content ' • , milk t ,

"--------------==--=====¥==~.~~--~--------'-"F~1~v~e~s~t~r~o~k~e~s~.~.~.~.~.~.~.~.~.~.~.~.;.;.~.,' __ ~l~O~,~O~5~0 __ ~'----------­,- " I

:, __ ~~~e~n~s~t~r~o~k~e~s~.~.~.~.~.~.~.~.~.~.~.~.~.~.;.~.,;---=1~4~.~2~50~--T:---4~,~20~O~--:

'_~F~1f~t~e~en~~s~t~r~0~k~e~B~.~.~ •• ~.~.~.~.~.~.~.~.T'--~1~6~,~8~2~O~_,--~2~,5~7~O~-' · , . '_~fw~en~t~y~s~t~r~o~k~.~s~.~.~.~.~ •• ~.~.~.~.~.~.~.,_~1~7~,~O~1~5~_,----~1~9~5~-' • , , t

:~Th~ir]l~~S~t~ro~k~.~s~.~.~.~.~ •• ~.~.~.~.~.~.~.,:--~l~6~,~4~O~O~_,--__ ~6~1~5~--'

'_~F~i~t~t~1~8~t~r~o~k~e~s~. ~.~.~.~.~.~. ~.~.~.~.~.~.~.T'---1=4~,9~2~O~--r'--~1~.~4~8~O~--' • i , , Per oent inorease due to agit .. t1on ••••• 6~ • ==========================================='

The reslll.ts secmred ... 1 th the four samples of

milk seem to indicate that agitation .. ~t.rlal17 affeots

the n~ber of baoteria, when measured b7 the agar plate

method. When milk i8 thorough~ "ili tated the olump and

chains of bacteria break up and form separate oolonies,

hen samples of milk were shaken twenty to thlrty times

there was an inorease from 25 to 69 per csnt. Judging

from these relllllts it 1s very obvious that a large per­

oentage of the increase in b~terial oontent whioh took

plaoe in the processing of milk was due to agitation and

not .ntire~ to cont!U'l1nation. 'rhe peroent"ile of varl~

ation was always greater when the flora of the mllk was

dominated by Streptococous.

After making a study of the roaul ts given in

tables 15 to 18, lnolusive, it is conoluded that the

milk eamples and the dilution bottles should reoeive

twenty-fivs strokes eaoh, in order to 1nsure thorough

ag1tation and uniformity of results.

The results secured 1n this exp9rimont oonf'rm

the rules giTen by the Amerioan Publio Healtb Association

f or m1lk analyses, whioh state that "Eaoh sample of milk

and the corresponding d1lution bottle should be shaken

twentl-f1ve times.

-35-

PARr III. DETERl.l1IIUIG TEE YEAST, llOLD, AND BACTERIAL

CON'rENT OF CREAl! DURING THE VAIUOUS OPEllA'UOl!S

IN EVTTER-KAKI NG

Uany buttermakers are unaware of the baotorio­

logioal changeD whioh take plaoe during the various

operations 1n buttermak1ng. This inTestieation wIll con­

sist in following the baoterial ohanges that take place

In the buttermaking prooess at tho V. P. I. Creamery.

B.Y ueing raw oream of good, medium, and poor qualIty, it

is pODsible to find the eff1oienoy of pasteur1zat1on and .'

the effect of neutralization on the number of bacteria.

Uore attention will be given to the yoast and mold

oontent, 9ince they are a more rel iable index ot keeping

qualIty than the aotual number of baoter1a . Large

numbers o.t flavor and aoid-producing baeteria do not

Jeopardize the qual1ty of the butter, but are oons1dered

very benefioi .. l. It is thought that the orelll!\ used In

this work would be s1milar to t han found on the plntform

of any buttermak1ng plant.

Sin •• there was not enough surplus oream avail­

able to allow but one survey ot the buttermaklng prooess,

it was neoessary to f ollow the ohanges whioh took plaoe

in the least and mold oontent of cream and butter when

pasteurized and churned under a preaaure of carbon

dioxide.

-36-

Historical: In 1920 Lunda made a study of the

mioroorganisms in butter and ooncluded that a large

number ot the molds in pasteurized creamery butter is

due to oontamination following pasteurization; this

eepeciall,y oocu.rs in the ohurn. Lund9 also tound thst

yeast and mold are killed by pasteurlzing at ordlnary

temperatures. Bouska and BrownlO reported that the

ohurn may be an important Bouree ot baoterla unless it

is carefully treated. They also tound that more organ­

isms are added to the butter during the working than

during the ohurning, because of the organioms belng

toroed out ot the working parts ot the churn. Gregoryll

shows that tho ordi~ oleaning methods do not elim1-

nate oburn oontamination. His studies reveal the tact

that the bacteria in the churn are far more numerous

than the aold-produoing organisms, whioh are largel,y

yeast and maIda. St1ri tz12 suggeeted that yeast and

mold oounts should be used 8S an lndex to the Whole

buttermaklng prooess, rather than to pasteurizatlon

only.

In 1931 Llbbertl3 isolatsd 57 yeast and mold

oUl tures from various ohurns, and all exoept three of

the yeast oultures grew on a medium oontaining water,

agar, and ground wood fiber.

Uethod ot stugy: In making a baotoriological

study of the butter-maklng process 1 t ""8 deemed

-37-

unnecessery to ~ake counts on the actual number o~

bacteria s1noe moat acid-produciniS organisMs are bene­

fiDial and are essential to hiGh quality. Tho number

of yeast. and molds was determined by pl a ting out on

wort agar nnd incubating the plate s at room temperature .

The butter and Dream to be tested was melted and pipetted

1nto sterne petri dishes . This was 1'.eld in suspension

by having about one CD. of sterile water in eaoh dish.

Samples ... ere pl e.ted out in duplicate of one and t wo drop s

eaoh. The medium used in makl~g these count. had t he

following c omposi tion:

~gar shread s . ... ... . ...... 20 grams

'Ma.l t syru.:p.... . .. . .... . ... 40 cc.

SUcrose • ..• •. . ...... ... .. . 20 grams

Distilled w .. ter . .•..•...•• 1000 co.

The reaction ot this medium was not adjusted , s i nco a

a relatively acid medium is e.sential to L~ibit t he

growth of bacteria . All plates wer. incubated for a

period of five days or longer .

The number of proteolytio baoteria in the

butter and oream was determined by adding one cc. o~

.terile skim milk to fifty DC. of steril. agar and

plating out in appropria te dilutions. All plat es wo re

1ncubated t or a period ot 48 hours, at a t empe rature at

31 degrees Centigrade . Proteolysis was indicated by a

clearing a round the colony.

Li~olytio baeteria were deteoted by adding one

ee. of steti1e butter to f1~ty oe. of sterile agar, and

pouring into petri dishes oontaining an aliquot portion

of the sample to be tested. The 1ipo1ytio colonies were

deteoted by flooding the plate with a ten per oent

solut10n of copper su1~hate. The oolonies retaining the

stain were reoorded as 1ipo1ytio baoteria.

Collecting Samplee: The bacteriologioa1 surTey

made on the l a rge batoh of oream oonsisted in oolleoting

four samples. Eaoh sample lVas collooted in a sterile

bottle and the test was set up immediately. The first

sample was taken after ~ouring the oans of oream into the

paBteurizer. After neutralization t the second sample was

taken and the number of yeast and mold determined in the

usual way. After the oream had been pasteurized at a

temperature of 190 degrees Fahrenheit, for 30 minute.,

the third sample was taken from the pasteurizer. with a

sterile pipette. When the oream had oooled to a temper­

ature of 37 degrees Centigrade it was inooulated with a

pure oulture of streptoooccus Laotis. The ohurning

prooess was oarried on in the normal way and after salt­

ing the fourth sample was taken directly from the ohurn.

Results obtained from a determina tion of the

yeast and mold content of the samples are given in

table 19.

-39-

'l'ABLli: 19. Ilwllbee' of Yeas t and Mol d found in Sample. of Butter and Cream

~»le' 'No. ot'No. ot'rneubatlon ' : __ ~N~O~~'~T=r~.~a~t~m~e~n~t~o=f~S~am=p~l~e __ T:~Y~Ol~d~T:_Y~e~a=s=t~: __ p~e~r~i~o~d~ __ ' , 1 , Before Eaeteurization' 44 '18,585' & days , , , , , , 2 ' After neutralization , 28 , 7,560' 7 n , , , , , 3 ' After pasteurization ' 0 0 7 n , , .,---- , , , , 4 , Butter, after salting' 61 4, 7 "

After neutralization there was a considerable

decrease in the number at yeast and a slight decrease in

the number of molds per cc. of cream. Judging trom these

resulte the molds are apparently more resistant to an

alkaline medium than the yeast. When the pasteurizing

process waD carried on at a temperature of 190 degrees F.

it proved to be very effective in destroying yeast and

mold growth. Since the number of molds in the butter are

muoh higher, it appears that the churn is a more prolifio

souroe of mold then yeast.

These results tend to confirm the conclusions of

Coulter14 , in which he concluded that the churn is a

greater sauro. of molds than yeast.

Determlnl~ the. Effeat of .Oarbon Dloxla. on the !/UllIber

o~ Mlcroorge.nlsms Found in Butter and Cream

The author w~s very fortunate in being able to

secure samples of butter and cream from an experiment

Carrled on by a graduate student15 at the Virgini a

Palyteahn1a Institute. who was try1ng to find the effect

of carbon dloxide on the keeping quality of butter. The

crea.m was chu.Tned. and pasteurized. Ul'lder 8, high pre s sure

of carbon dioxide. Usually nine or ten gallons of cream

was prooe88ed at the time by this method.

When the cream was delivered to the creamery it

was thoroughly mixed and a sample taken in a sterile

bottle. then analyzed for the nUlllber of yeast and mold.

After neutralization the oream was poured into a special

ten-gallon oan. whioh was equipped wi th a -pipe leaa.ing

to a tank of oarbon dioxide. Another p1po was oor~eoted

to the churn 1n a similar manner. The oream was

continuously ~ubject to ~ carbon dioxide a tmosphere Whi le

1t was be1ng pasteurized. The cream gas pasteurized by

heBt1ng in a large Tat of water for 45 m1nutes ~t a

temperat ure of 185 degrees li'a..'lrenheit . When the pressure

of carbon dioxide was released the second sample was

taken. After the oream had cooled to a temperature of

37 degrees Centi grade it was 1nooulated wi th a vi able

oulture of streptococous laotus. The cream was then

inoubated for twenty-four hours and ohurned un4er a

presllUre of oarbon dioxide. Immedla tely ufter ohUl'll1Dg

the th1rd sample w~s taken to find the effeot of carbon

dloxide on the 1'ill1shed product.

fhls same prooeduro was followed On other

batches of oream, with and wlthout the use of oarbon

d10xlde. ~i8 was done ln order to obta1u results on

untreated samples, for oomparison.

Reaults Obtained after Treatment w1th Garbon

Dlox1"l Three batohes of 01'<18.111 were shurned ln the

preaonoe of carbon dioxlde. In ever,y oase there was con­

s1derable varlatlon 1n the quality of the raw oream used

in the experlment. mhe effect of oarbon dloxlde on the

number ot yeast and mold will be found in tables 20, 21

and 22. The number of proteolytio and llpolytic

bacteria were determined on one 8ample of butter.

1'ABLE 20.

,

• 1 a. , Haw orewn 'l,890'lZ,160' - • , 5 daYlI' , • !sour! • • • • • , , , Oream past. , , , • L 1 b • with oarbon • 4- , 0 • - • , 6 n • , • dioxide • , , t· , lliitter cliurnea' , I , i • 't

• 1 0 • with ca.rbon , 123 , 9 • - , - , 5 " ,

, , dloxide , • • • • • • , , , I , , •• , 1 d , Butter , , , 27 • 245 '48 Hre. t

• • • f , • • I

-42-

!rABLE 21. Number of Yeast and Ilold Found ln Cream and Butter when Treated Wlth and Wlthout

Carbon D10xide 'sample' Treatment Reae1ved 'Bo. ot '50. of 'Incubation ' t lio. , , , 2, a ,

, , , , 2 b , I I

I I , 2 a , , , , , 2 d , , t

TABLE 22.

, 1I0lds ' Yeast , Perlod

liaw cream (sour) , 4, 130 , 3,010 , 5 days , , , Cream past . wlthout , 17 , 0 , 0 "

aarbon dloxide I , Butter ahurned , 4 , 1,690 ' 6 "

wi thout CO2 , , I I

Butter ohurned I 21 , 0 , :; " wlth CO2

Number of Yeast and 1I01d Found in Butter when Treated wlth Carbon Dioxide

, , t

, , t , ,

'Sample ' t lio. ' Treatment aeaelved '10. of '10. of 'Inoubation '

, lIoldB I least' Period I

I 3 a , Sweet oream 4 I 120 , :; days • , , I I I- I I , I 3 b I Pasteurized ••...... • Sample bottle was I I oontaminated I I , I 3 a , Butter ohurned with I 9 I 0 I :; days

oarbon d10xide I , , , I 3 d , Butter churned with- I 29 I 6 I :; "

I out carbon dioxide I

In every aase the oream that was paateurlzed wlth

oarbon diox1de w~s always h1gner 1n the number of molds

than the yeast. From th1s abservat10n it appearo that

the mold. are more resistant to heat as well 0.8 carbon

dioxide. The yeast were k111ed ln every b tah of aream

that was pasteur1zed. There wa. a decrease of 99 per

I

• I

I

I

I

• I

-43-

oent in the number of molds in each sample of pasteur­

ized oream.

PART IV. DXTERllINING THE INFLUEllCl! 01' V.ARlOUS OP1i:RATlOIIS

ON ~ BACTERIAL CONTENT OF ICE CREAK

The inoreaslng popularity of 10e ore~m ln ever.1

state is bringing it under oloser lnspectlon by the health

offioer.. Dur1ng the last few years enout;h d~ta has been

acoumulated to prove,beyond a doubt, th~t freezing oan

not be depended upon to kill 81 thor pathogenl0 or non­

pathogenic bacteri,.. Large numbers of baotorla do not

necessarily oonde= i08 cream any more than s .... U numbers

neoes.arily lnsure its sanitar.1 quallty. However, we have

oom. to aS800iate an exce.sive number cf baoterla ln most

food products with inferlor materials and unsan1tar.1

praotioos. This ls partlcularly true in the dair.1

1ndustry where total numbers 01' baoteria have been uaed

as on index to tho sanitar.1 quality. In order to supply

the publio with a wholeBome produot, baoterial standards

for ioe ore&m have been established. Suoh standards,

plus intelligent inspeotlon supplemented by oareful plant

operation, vnll aid considerably in manufacturing ice

oream with a low baoterial oount. If the manager of an

ioe oream plant had a knowledge of the operations whioh

-44-

materially add to the bactar18.l oontent, detinite sani­

tary steps could be taken to avoid suoh oontam1nation.

1I9.l\Y times dur1ng the past tew years sanitary

lnspeotors, health offloers and plant managers have a sked

the questlon "Whloh operat10n or operatlons ln the manu­

t~cture ot 10e oream are malnly respons1ble for hlgh

b..eter1al oounts". The present work was undertaken lIartly

to answer the abavo question.

Previous Studles: Several investlgatlons have

been made, from .. baoteriologioal standp01nt, of .aoh

step 1n the prooess ot ioe aream manufaoture, but most of

the investigations have been made on 1ndlvidual operatlons .

RummerlO report.d that ice cream with a low baoterial oount

can be produced by pasteurizing and homogen1zing the m1x.

He also found the homogenizer to be a gross souroe of

oontam1nation. Pennlngton and 'IIalker16 were among the

first investigators to study the influenoe ot manufaotur­

ing operations on the bacteri al oontent of ioe cream,

Their work reveals the ract that after p~steurlzation the

ioe cream contains a relatively large number ot etrepto-

00001.

Hammer1? mad. an 1nvestigation on the number Qf

bo.cterle. found nt various intervals during the manufac­

ture of 10e oream, and conoluded that 1t 1s possible to

produce 10e cream with a low baoterial oount wlthout the

use of expensive methode. The studles of Hammer and

.I -45-

GOBs1V , on the influenoe of hardening and storage, show

that there is no inorease in the number of organisms con­

tained in ice oream under proper storage, whIle there Is

oommonly a decresse.

The Influence of storage on the number of baoterla

in ioe .ream has boen studied by several workers. GordonI8 ,

Eatenc-and lIaBonl .. , and Ellenbarger20 have oovered this

phase of the problem very adequately.

Uethods Used: Bacterial count. were mede on

samples of 10e oream taken after variouB operations in

the manufaoture of 1ee oream 1n the 10e orea .. laboratory

at this college. Usually the batchos ot ioe oream were

rather small, but they were manutaotured with equipment

operated on a oommeroial basis and under praotioal oon­

ditions. The samples of various batohes were taken at

random trom Jlll1uary 2 to Apr1l 5. The e.rrangement of the

.. e..hinery 19 oomparable to that fcand in an up-tO-date

plant.

All straIners, oans and other utensil. were

thoroughly steamed and the treezer oarefUlly soalded.

The pasteur1zer was scrubbed with 0. brush and oleaning

powders, fOllowed by a r1nsing with hot water. Hot watsr

was run through tbe homogenizer with oonsiderable foroe.

Eaoh sample was colle.ted in a sterile bottle

and oooled immediately. The samples were taken at the

following point. during the prooess of ice oream

,

aanufau~r8' Arter pasteurization. atter homogeni­

zat10n, atter ooollng, atter aging , und atter freez1ng.

All samples were melted alowly and pIa ted out on the co.

baels. The method ot plating, diluting, and kind of

medium was sim11ar to that out11ned by the A. P. H. A.

for analysis ot milk. Every dilution was plated out in

duplioate, and the average count tor the two plates

represented the tinal count. All s","ples studied; with

the exoeption of one, were ~nl11a lce oream. %he tlavor­

ing W~B added ~t the time of freezing.

The lIl&ch1nery consisted ot one tubular cooler,

one homogenizer, one Killer ice cream ~reezer . and a

75-ga11on pusteurizer, In additlon to the above equip­

ment, there were about ten l O-gallcn oans and about twenty

teet ot connect1ng pipe used i n the manufaoturing process.

Atter the mix btld been partly pasteurized it was

atarted through the homogenizer. this resulted in a miX

tb9.t wc.s not uniformly pasteurized. For th1s reason the

f1rst port1on ot the mix was higher in baoterial con~ent

than the last tew cans. In v1ew of this prooedure tho

last tew oans wers a l ways used in this inTest1gat1on, so

as to inv~re unitormity ot results.

Yost Frequen~ Souroes ot Contl\lllination: There

are three pr1n01pal sources ot baoteria 1n ioe oream.

First, tt.e .... ter1als trom uhioh the i Os Cl'eam is made;

this can be oontrolled by thorough pasteurization.

Seoond, the machinery equl;ment; thl. i. the ~ost

Q.U't1eult source of contamine.tion to control. However,

some part. of the equlpmen t Gan be thoroughly oleaned 80

as to maintain a product ot low bacteria oount. Third,

the person handl1ng the produot; ottentimes this beoomes

a great Gouro. of oontamination, eapoolally if the oper­

ator is oareloes. ~he oont~1nAtion arising :from this

eouroe oan be kept to a minimum by keoping olean hands and

"earing white clothes.

Results Seoured: ~he result. seourod btter

:following :four batches of ioe oream mix are presented in

tables 23 to 26, inclusive.

TUlLE 23. Effoct of the Various Ope .... Uone on the Baoterial Contant ot Ioe Cream lUx

i Srtmple 1 'No.ot biot.'cbinge in' , No. , ~reatment of Sample 1:per 00. of , baot. , , , , miX , oontent , , • ; , , 20 a , Pa.st. for 25 min.at 13~0 ) ' 1 15,000 , , I , • , 20 b , HomoG· at 3500# Rressure 24,000 , 9,000 , , , , , , 20 c , Cooled to 580 li'. • 32.23~ 6,235 , , , , , , 20 d , In O&rl6 betore agin5 , 33,000 , 765 , , ; , , , 20 e , In cans after as' ng , 45,120 I 12.120 , , ,

Vanilla 10e oream, I • , 20 t , 60,& overrun 34,960 '-10.160 , , I Vanll16 ice oream, i I • :.20 g

, 9510 overrun , 15.'611 '-29.355 , ,

ChooQlat~Ioe oream, I I , , 20 h , 95,. overrun , 17 ,830 '-27.470 , ..

Eft.at ot the Various Op.~tion3 on the lIaaterial content ot IC8 Cre .... Il1x

, , 'fto.of baot. 'Change in' 'Sample' treatment ot Sample ' per aa. ot' baot. ' • No." mix ' con~8l1t ' '~~=P===-=-=--=~=====---=F~~~~~~~~ "

, 21 a ' Fa.t . tor 25 min.at 1400 P. 370 , , I ,

, 13,820 , 13,450 r

, 21 b ' HOllog. at 2600# pressure , I

, 21 0 ' Cooled at 600 F. ,- , , 21 d ' In oans before aging , I

•

, 16, 470 I , , 18,000

TABlE 35. Eftoo t ot the Various Oporations on the lIadterlal lSontent ot an Ice or ..... lUx

2,665

1,535

. • , , , , , ,

, t tHo. of baot. 'chs.nge in' 'Sample' treatment ot Sallple 'per co. ot· bact. • ' __ ~B~0~'~' ______ ~ ______ ~-= ________ ~' ___ m:;1x~ ____ ~'~G:o~n~t~e~n~t~. ,- , '_~2~?~n~'_F~s~s~t~.~f~0~r.£25~m~i~n~.a~t~1~4~6~o~F~.~, __ ~3~1~0~1~0~~~ ________ ', , t ,

'~2~2~b~'~n~0~m~0~G~.~a~t~2~30~0~~~p=rc~s~ou~r~e __ T' __ ~7L,a~50~ __ r-~4~,2~4~O~', ,- r t, :,.!2~2~0~'~O~O~O~1~O~d~t~o~6~O;O~F~'~~ ______ T-__ 28~,2~O~0~ __ ~ __ ~9~5~0~:

, In can. after sglilg , :,~2~2~d~: __ ~t~o~r~3~2~b~0~u~r~s~ __________ ~t--"ll,e~50~ __ ~; __ ~3~.~6~5~0~:

, 22 e t Vanilla 10. cream- 14 ,100' 2,250 ' , VanIlla. 10e oream t r '._~2~2~t=='=====9~5~e~O~v;.~rrun~~=========='==~e~!~e~eo~==='-~O~.~2~6~0ba'

-Tho ice ot"e"'" ",,"s thor oughly shaken to ol<pe1 dr.

TAl3!.E 26 .

'i t

-49-

E.f1'oct of t he V",,1oml Operat ions Oll th(l llaoterial Cont ent 01' An Ioe Orou lola

- 'Iolof bact.'ChinBe In' ' Sample ' Trea tment 01' Sample ' ~per -cc. of' baot. ' I No . ' 1 mi.x • content ' ,"~~~------~-=--=~. ~--~·----"--"F~·~·W=~t---:~-----Tf~~~~-"

4,225 , , 11,275 , '/,055

ll,4!)0 125 , 32,700 , 21,300

I

33,900 , 1,200 I

,

"Tho lco Cl'oam """,p10 WaS thorough.ly shvJ<en t o oxpel all air.

~,e 1n1'luenae 01' pas teuri zation on the bQcter1a~

oontent 01' an lee oream miJc: )leo!luse 01' the diverse

sourOes 01' solld and 11quid ma ter1ala oontained in the i oe

cream miX, a bQater1al oount was not made 01' the il1gredients

bei'ore pastour1zat ion , However, nono of t he samples were

v917 high in baoter ia l numbers, nor WIlS any sample completely

ster1le • .:!tltr PllOteur1z"tion. The e:t'1'10iency of pasteur­

ization varied 1'rom 15 . 000 in one sWllple to .. mi nimum of

370 baoter1a per 00. 01' miX. Acoord1ng to the studies ot

Fab1an21 , an ioe ar 80m n.1x nhould be pasteul'1zed at a

temperature ot 150 degrees Fahrenheit for 30 minutes.

Beoause 01' the nature ot the mat8r11>ls, an ice oream miX 1s

not pastsurized as readily as mi lk. ..von though the

baoteria l content of the mix in rel at1voly low it 1s thought

-150-

th .. t bstter result .. oould have beon s.""rad 11' the II1U

" .... tborouehl¥ pasteurized berore hOlllogen1zaUon wa.

st .. rted.

The lnt1~~~~t-Romogen1zQti~~~on the baoter1al

oontent of an ioe ore"",_mi;! After tho mix had been heated

to a temperature 01' 135 - 145 degreea Fnt.r.hholt tor about

15 minutes, it was started through the homogenizer where

it "as under .. prossure ot 2500 to 2600 pounds.

An inspeotion 01' the t~res (; i von in tables 23 to

26 sho"s .. a&Ximum inorease ot 13.400 and a min1mwn in­

orease 01' 4,240 baoteria per oe. ot the nix. A alight

inorease in the bacter i al oontent e~ always be expeoted,

sinoe this maohine is hard to olean and has a tendenoy to

breBk up the olumps 01' bacteria. As the procaas was oon­

tinued. the presumption was that t he contamination would

beoome lesa due to the wsshine, etfeot. However, most 01'

t he inarease tound in the t ables is pra 8um~bly due to

B61ta t1on, 8ince moat 01' the eamples w.r~ not caught until

most of the mix had been homO£enized. It 1A thought that

moat of the b .. oteria bad been v/a.shed out before the

samples were oolleot •••

The Int1uenoe 01' oool~ t he ice or.am mix o~

the baoterial content. Atter each mix had paned through

t he homogenizer it I'fU forced to the cooler, ",here it was

oooled to 68 degrees lfahrenhe1 t. The tirst part ot the

mix p .... ing over the oooler "aa higher 1n baoterial oount,

-51-

beoause 01' tho slight washing etteot. In th1s experi­

ment the samples were not taken unt1l most 01' the mix

had passed over the oooler . ~ ooo11ne the m1x trom s

temperature of 125 degrees to 66 degreos Fahrenheit it

1s thOUBht thn t this sudAen ohango WDU14 have hlld some

effect on the number of bacter1a. In ever,v oase there

was an inore"oo in the number of bacter1 .. per oc. of the

mix. The smallest increaso in any of the oamples wao one

psr oent and the areatast inorease was n1netoen Dor oent.

There is a J)Oss1b111 t.v that e. tow ot the baoteria Vlere

1<111ed in the sudden ebango of temperature, but it Bt10h

.. decrease existed it was overcome by the con~1no.t1on

rece1vod by the cooler. Despite the taot that this

oporation inoreases the bacterial oontent , 1t 1s 1n41s­

pens1ble to keep bacterial aotiv1ty to a m1n1mum.

!!he 1nfluence of a!!J.n6 on the be.aterh.l oonte!!t

01' an 1ee oroam m1xI !!he mix was agod at a temperQturo

at 32 to 35 degrees ~~onhe1t. At this tom~er~ture some

increaso 1n bacter1ul growth took plo.oe. !rhere was ..

Slight varlat10n 1n temperature, but not more than two or

three degrecs. It haa been found by many Ylorkers tha.t

ag1ng an 10e aream m1x 1s very benetio1al 1n inoreaslng

visoos1ty, and th1s 1nfluenaes the yield of the f1nished

product. !rhe influenoe of this proaess can be tound 1n

tablos 23 to 26, inaluaive. Every batah shewed an In­

orease 1n the number of ~~oterla por 00. ot the mix.

-52-

!he samplee showed an increase ranging trom 7 per cent

to as high as 187 per cent. This inorease shows oon­

olusively that the tempera~ure was not low enough to

inhibit the growth ot all orflBnisms. However, the

baoteria commonly found in milk do not grow very rapidly

at this temperature. Aocording to the studies of

llarehaU22 , 1 t 1. very obv10us t ho. t oerta1n ot the

spore-bearing non-acid bacteria will develop rapidly at

a temperature ot 10 degrees Cent1grade.

The 1nfluenoe of freez1ng on the bacter1a~

oontent ot an ioe oream mix: ~he mix was usually fro.en

about two days before it was made. This period would

vary according to the demand tor the finished produot.

The temperature of the brine at whioh the m1x ""8 :frozen

ranged trom -10 to -5 degrees Fahrenheit . All samples

were oollected just as the mix left tho froezer. There

WaS a variation In the &oterlal oontent oorresponding

to the overrun peroentaee. As it would be expected, the

higher the overrun the tewer the number ot baoteria per

oc. of ice oream. When the overrun peroentage was con­

Sidered the ioe orerun samples were not shaken betore

making the dilutions. .\.11 other ioe cream s8lDples were

thoroughly shaken, to exolude the air incorporated

during the treezing prooees, before dilutions Were made.

It is thought that the breaking up of clumps ot baoteria

during the froezing process is muoh less than th"t due

-53-

to homogenization. When the overrun was not oonsidered,

the greatest increase was 16 per oent and the greatest

deorease was 66 per cent. Most of the inorea •• i8

probably due to contamination from the freezer.

~e influence of storage on the baoterial con­

tent was not .tudied with these samples.

CONCLUSIONS

aesults reported show that milk, butter and ioe

oream oan be produced with a low baoterial oount by the

methods employed in this plant. ~be effect of eaoh step

in the prooess on the baoterial oount has been de~lt with

separately and the most signifioant oonolusion. found are

as follows.

1. This work oonfirm. the oonolusions of other investi­

gators , that.- the utensils and equipment in

which milk io handled are prolifio souroes of

baoteria when not thoroughly oleaned and steri-

11zed.

2. The baoteria in freshly washed ten-gallon oans are

destroyed when they are .teamed for twenty

seoonds or more. Whsn the oans are s teamed less

than twenty seconds, oonsiderable growth takes

I..:plaee.

-54-

3. More contamination took plaoe durine the heating

and filterinB operation than with any other

operatlons in the plant.

4 . When the number of baoteria in milk are measured

by the pl ate method, the oount is muoh greater

after pumping tho milk than before .

5. The oooler was found to be a oonsistent souroe of

oontaminatlon. In no oase was the lnoresee in

the number or baoteria per ce. cf milk exoeption­

ally high nor exceptionally low when it .as

allowed to pess OVer the oooler.

6. The results given ln this experiment tend to confirm

the results secured by the Amerioan Publl0 Health

Assooiatlon for analyses ot milk, whioh statss

the. t "Each sample of milk and the oorresponding

dilution bottles should be shaken twenty-five

times." When the mllk is thoroughly agitated

the olumps and ohains of baoteria break up and

form separate oolonies on the agar plate.

7. li!olds found in maI".cet 01'eam appear to be more resist­

ant to an alkaline medium than the yeast.

8. Sinoe the number of molds 1n the butter are muoh

higher, 1 t seems the. t the churn is " more pro *

11fio .aurae ot mold. than yeaste.

9. Carbon diox1de was more effeotive in destroy1ne yeasto

than 1 t was in deDtroyinB molds wh10h frequent

-55-

market cream nnd butter .

10. When the 10e oream mix was homogenized there was

always Q distinot increase in the number ot

b~oteria when measured by the plate method.

The inorease may be npparent rather than real.

11. When the 108 erellm mix was aged there was an in­

crenae 1n the number of baoteria ranging from

7 to 187· per cant.

12. After the mix is llssteurized every subse \luent

ollerntion has a tendency to inc!'ease the J)late

oount.

13. The number of bact.ria was found to b. nireot1y

prollortions1 to the overrun percentnge.

BIllLIOGRAl'1!Y

1. Backhaus. W. nnd Cronh.eim, W. Uber aset10he

2.

~!llohgew1nnung . Eer. Lannd" , InDt. Un1 v.

Konigbs. I, Heft. 2, Pll . 12-32. 1898.

Bergey, D. H.

i n mill:.

-- Sources and natu~e of bnotar1a

Penn. Dept . of Agr . ll-.ll. 125. 1904.

3. Rnsee1, H. L. and Roffman, Conrad -- l\ectoriolog1ca1

t est of bottle washing device. Wisc. Agr. E%pt.

stu . Ann. Rep. ?2. pp . 227-231. 1905.

4 . PruohQ, J. U. and Wetter, H. H. -- Germ oontent

of m11k. Unlv. of Ill. A8r. Expt. St ... Bul.

199. May , 1917.

5, Oonn, H. W. -- B~oteria 1n m1lk and 1ts products.

storrs Agr. Expt. 8ta. Bu1. 4. 1889.

6. Harding, H. } .. o.nd Wilson, J. K. -- Etfeot of

methods of hancUing on tho germ oontent of

milk. II. Y. A8r. Expt. St<>. Bul. 317. 1909.

7. Breed, R. S. -- rile mlorosoopie count. 11. Y. Agr.

Expt. 5ta. Bu1. 49. 1925.

8. Lund, T. H. -- Yeast and Holds in Butter. II. Y.

Prod. Rev. Amer . Cry. 51:510-~12. 1921.

9. Lund, T. I!. -- Yeast and 1I01ds in Butter and Cre..,..

II . Y. Prod. Rev. and ~.r. Cry. 48:282-284.

1919.

10. Bouska, F. W. and Brown. J. C. -- The s1gn1fioanoe

:~~ of yeasts and in pasteurized butter. Wis.

UniT. Studt •• in Soienoe 110. 2, 131-38. 1921.

11. Gregory, H. W. The churn &s a faotor in tho con-

taminat10n of butter. N . Y. Prod. nev. and Amer.

Cry. 50:18-22. 1920.

12. St1rttz, B. A. -- Yeast and Kold count and their

relation to pasteurization of oream for butter-

making purposes. ..~. Sei. 362-71. 1922.

13. L1bbert. 11. S. Churn contam1nat ion and methcds of

oontrol. Jlat. Butter Jour. 22: 16-18, 1931.

-57-

14. Coulter, S. T. -- The oaa~renc& of mold in

butter. Pro •• of the 31st =d 32nd Ann. ConT.

Bat. Cry. Buttormskers Asao. ~p . 5-8. 1931-32.

15. Ham:mer, B. ~' t -- E!l.oter1o. 1n 10e oream. Bu!. 134,

lowe. ii.gr. EXp. ate.. 1912.

16. Penntngton and WaL"'er -- Bo.ator1oloeio,,1 anrvoy ot

00 .... no1 .. l 100 ere·'.!Il. !i . Y. lied . Jour. Vol. 86.

Il . 1013.

17. Hammer, B. W. and Coss, E. F . -- Docteria in Ioe

Cre!\!!l. Iowa .!.gr. ExIJ. Stat il'~l. 174. 1917.

18. Cordon, J . C. -- Report on ice ore~~ .x~1nations

outlined 1n the Washington hearing of ioe crown

nanu1'aoturers. T~.e Nat. AUM. of Icc ere .... II1'g.

19. Eaten and M~Bon -- The baoter1a in ioo oroam . Conn.

Agr. F~Il . Sta. E>~l . 83.

20. Ellenborger, R. B. -- A study ot baoteria 1n ice

oream during storage. Memoir Ie, Cornell Agr.

Exp. Station.

21. Fab1an, F, W. -- Product1on of Iao Cre~m with a low

bncterbl cont~nt. J.l1ch . Agr. ExIJt. Sta. Bal.

11l9. 1927.

22. Ilarshall, C. E. -- l!1crob10105;Y, Third Edi tion,

p . 458. 1921.