Food Control 16 (2005) 333–338

www.elsevier.com/locate/foodcont

Aroma compounds as markers of the changes in sherrywines subjected to biological ageing

Jose A. Moreno, Luis Zea, Lourdes Moyano, Manuel Medina *

Department of Agricultural Chemistry, Faculty of Sciences, University of Cordoba, Campus de Rabanales, Edificio C-3, 14014 Cordoba, Spain

Received 6 September 2003; received in revised form 13 March 2004; accepted 15 March 2004

Abstract

Capillary-column gas chromatography was used to determine 63 aroma compounds in 9 very pale sherry wines, fino type,

subjected to biological ageing under industrial conditions for 1, 3 and 5 years. The contents in aroma compounds were related to the

wine ageing time by means of a simple linear regression model. The compounds that exhibited a high correlation coefficient

ðr > 0:90Þ and simultaneously a high odour impact value (OAV>5) were additionally subjected to principal component analysis.

The first component was found to account for 93.12% of the changes in such compounds during the biological ageing process. The

greatest contributions to this component were those from sotolon and 1,1-diethoxyethane, both related to the acetaldehyde pro-

duced by the metabolism of flor yeasts, and Z-whisky lactone synthesized from its precursors extracted from the casks wood where

the wines were aged. The use of these compounds as markers for biological ageing is advantageous because their changes in

concentrations is taken into account as well as their odorant impact.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Sherry wine; Biological ageing; Odour impact; Wine aroma

1. Introduction

Sherry-type white wine called ‘‘fino’’ is obtained

through a long process (about 5 years) of biological

ageing under the action of so-called ‘‘flor yeasts’’,

which develop aerobically on the surface of wines

containing 15–15.5% ethanol (Bravo, 1995; Suarez,

1997). Fino wine exhibits special sensory featuresincluding a pale yellow colour, a slightly bitter flavour

and a complex aroma. This last is developed during its

biological ageing, largely as a result of the action of flor

yeasts as well as the contribution of volatile com-

pounds extracted from the wood casks where the wine

is aged. The method traditionally used to obtain fino

wine, locally known as ‘‘criaderas and solera’’, essen-

tially involves mixing less aged wines with more agedones several times in a year (so-called ‘‘roc�ıos’’). Thistechnique assures the maintenance of a level of nutri-

ents for their consumption by the yeasts, as well as

homogeneity in the composition of the wines with a

*Corresponding author. Fax: +34-957-218606.

E-mail address: vitenol@uco.es (M. Medina).

0956-7135/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodcont.2004.03.013

same ageing degree. More information about this

exclusive wine ageing process can be found in papers

by Domecq (1989), Zea, Cortes, Moreno, and Medina

(1996) and Moyano, Cortes, Zea, Moreno, and Medina

(2000).

Acetaldehyde is synthesized from ethanol by flor

yeasts by means of the enzyme alcohol dehydrogenase in

the presence of NADþ (Garcia-Maiquez, 1988). Theincrease in the concentration of this compound is one of

the more outstanding features of the biological ageing.

According to Zea, Moyano, Moreno, Cortes, and

Medina (2001), the acetaldehyde content allows the

differentiation of fino wines from other types of sherry

wines produced by oxidative ageing. Acetaldehyde is

responsible for the pungent character typical of fino

wine and it directly contributes with ethereal and ripeapple notes to its aroma. Likewise, this compound is a

precursor for the synthesis of other odorant products,

thereby indirectly contributing with several distinctive

notes to the aroma profile of wine (Etievant, 1991). On

the other hand, flor yeasts increase the contents in other

aroma compounds such as higher alcohols and acetates,

ethyl esters, lactones and terpenes (Zea, Moreno, &

Medina, 1995).

334 J.A. Moreno et al. / Food Control 16 (2005) 333–338

Traditionally the winemaking industry of sherry hasused the acetaldehyde content as a marker for the status

of biological ageing. However, the relationship of its

content to the ageing time for fino wines is rather

complex because its production is influenced by the

population and metabolic activity of the flor yeasts used,

the temperature, ethanol content and the redox poten-

tial, among other factors (Garcia-Maiquez, 1988; Mar-

tinez, Perez, & Benitez, 1997). Particularly, it has beenpointed out that flor yeasts are very temperature

dependent microorganisms, mainly growing about 20 �C(Ibeas, Lozano, Perdigones, & Jimenez, 1997). There-

fore, their period of peak activity lasts only a few

months each year depending on the temperature con-

ditions of each cellar, leading to wines aged for a same

number of years but with different composition making

their commercial standardization difficult. This difficultyis increased by the effect of the periodic transfers in-

volved in the production process, which mix wines with

rather different acetaldehyde contents. As a result, it is

well known that some commercial fino wines have

similar acetaldehyde contents but differ markedly in

quality, mainly in relation to their sensory properties.

Therefore, one must be cautious in adopting this com-

pound as a marker for biological ageing of fino wines.However, from an industrial point of view, an effi-

cient procedure to control the biological ageing of wines

is required to standardize their quality in relation to the

ageing time, in this way to reduce the production costs.

It would thus be of great interest to control the process

via alternative compounds exhibiting a high correlation

between their contents and/or sensory properties and the

ageing time. This would provide an objective criterionfor estimating the degree of biological ageing of fino

wines produced under slightly different environmental

factors and cellar practices.

In this work, we studied the relationship between the

compounds with an odour impact in fino wine and the

biological ageing time using a linear regression model,

with a view to the potential use of such compounds as

markers for this special wine ageing process. This wouldresult in a better understanding of the production pro-

cess, by improving the standardization of these wines in

order to better satisfy the demands of the consumers.

2. Materials and methods

2.1. Wines

Nine very pale sherry wines (fino type), subjected to

industrial biological ageing process in American oakcask, selected by expert tasters as more representative

among the wines produced in 21 cellars from Montilla-

Moriles region (southern Spain), were used. Three of

them corresponded to wines biologically aged for 1 year,

others three for 3 years and the remainder for 5 years.These last samples are commercially considered as typ-

ical fino type sherry wines. It must be pointed out that

the blend of less aged wines with more aged ones is an

industrial practice in the biological ageing of sherry.

Because this technique is applied in all the cellars,

indirectly it leads to soften the differences among them.

In this work, three different samples were taken for each

ageing time to consider possible slight differences amongwines with a same ageing degree.

2.2. Experimental analyses

2.2.1. Identification

Each one of the 63 aroma compounds analyzed was

identified in previous laboratory works by means of its

retention time, coeluted with a standard solution of

commercial product, and confirmed by Mass Spec-

trometry (Hewlett-Packard 5972 MSD).

2.2.2. Quantification

Acetaldehyde was quantified by using the enzymatic

test from Boehringer-Mannheim (Germany). For thequantification of the remaining aroma compounds,

samples of 100 mL of wine were adjusted to pH 3.5, 150

lg of 2-octanol was added as an internal standard and

then extracted with 100 mL of freon-11 in a continuous

extractor for 24 h. These compounds were quantified by

GC (Hewlett-Packard 5890 series II) in a HP-INNO-

Wax column of 60 m · 0.32 mm · 0.25 lm thickness

(Hewlett-Packard, USA) after concentration of thefreon extracts to 0.2 mL. Three lL were injected into the

chromatograph equipped with a split/splitless injector

and a FID detector. The oven temperature program was

as follows: 5 min at 45 �C, 1 �C/min up to 185 �C and 30

min at 185 �C. Injector and detector temperatures were

275 and 300 �C respectively. The carrier gas was helium

at 70 kPa and split 1:100. The quantification was made

by using chromatographic correction factors, calculatedfor each compound in relation to the internal standard,

in standard solutions of commercial products supplied

by Sigma Aldrich (Germany). This chromatographic

method has been validated in previous works (Moyano,

Zea, Moreno, & Medina, 2002; Zea et al., 2001).

The odour activity value (OAV) for each compound

was calculated by dividing its wine concentration by the

concentration corresponding to its odour threshold.

2.3. Statistical procedures

A linear regression analysis was carried out on thesamples for each aroma compound in relation to ageing

time. The contents of the compounds simultaneously

showing high correlation coefficients and odour activity

values were subjected to principal component analysis.

J.A. Moreno et al. / Food Control 16 (2005) 333–338 335

The computer program used was the StatgraphicsTM

(STSC Inc., Rockville, MD, USA).

3. Results and discussion

Table 1 lists the contents in aroma compounds of fino

wines aged for 1, 3 and 5 years, as well as their respective

perception thresholds. As can be seen, acetaldehyde,

ethyl acetate, ethyl isobutanoate, isobutanol, isoamyl

alcohols (2- and 3-methyl-1-butanol), ethyl hexanoate,

ethyl octanoate, 2,3-butanediol, methionol (3-methyl-thio-l-propanol), phenethyl alcohol, 4-ethylguaiacol

(2-methoxy-4-ethylphenol) and eugenol (2-methoxy-4-

allylphenol) always exhibited concentrations above their

perception threshold, so they can be considered active

odour compounds throughout the biological ageing

process. Also, 1,1-diethoxyethane, methyl butanoate,

ethyl lactate, Z-whisky lactone (3-methyl-c-octalactone)and sotolon [3-hydroxy-4,5-dimethyl-2(5H)furanone]exhibited odour activity after the first year of ageing (3

and 5 years), as did butanedione up to the third (1 and 3

years). On the other hand, acetoin (3-hydroxy-2-buta-

none) and hexanoic acid only exhibited activity in the

samples corresponding to the last year, and isoamyl

acetate in the first.

One way of quantification of the odour activity of a

compound is to determine its number of olfactory units(NOU), also so-called aroma value or odour activity

value (OAV). Such a value is calculated by dividing the

concentration of the compound in the wine into its

perception threshold (Cabaroglu, Canbas, Lepoutre, &

Gunata, 2002; Cutzach, Chatonnet, Henry, Pons, &

Dubourdieu, 1998; Guth, 1997). Thus, the odour impact

of a substance increases in proportion to its OAV when

this value is >1. Based on these criteria, the above-mentioned compounds (particularly those exhibiting the

highest OAVs) can be assumed to be those with the

strongest odour impact, thereby contributing to a great

extent to the aroma of fino wines and reasonably being

largely responsible of the sensory profile of these wines.

One simple way of relating changes in aroma com-

pounds to the biological ageing time is through linear

regression analysis. Thus, the contents in the com-pounds with a high correlation coefficient ðrÞ will fit

closely a straight line and be the most reliable analytical

markers for the biological ageing time in this type of

wine. As can be seen in Table 1, the highest linear cor-

relation coefficients were those for benzyl alcohol, ethyl

3-hydroxybutanoate and 1-propanol, followed by those

for Z-whisky lactone, methyl butanoate, 1,1-diethoxye-

thane, ethyl isobutanoate and butan-2-ol.Taking into account the odour impact, however, the

compounds better describing the biological ageing pro-

cess would be those that simultaneously exhibited a high

odour activity (e.g. OAV>5), at least at some point

during the process, and a high linear correlation coeffi-cient (e.g. r > 0:90) with time. This last condition leads

to results with a significance level at p < 0:001. Based on

these criteria, 1,1-diethoxyethane, ethyl isobutanoate,

ethyl butanoate, isoamyl alcohols, ethyl hexanoate,

methionol, Z-whisky lactone, eugenol and sotolon

would be the best markers. The presence of these com-

pounds in the wine can be ascribed to various sources.

Thus, 1,1-diethoxyethane and sotolon in fino wineoriginate by chemical pathway from the acetaldehyde

produced by the flor yeasts. The former is an acetal

exhibiting a strong odour impact on wines under bio-

logical ageing, to which it contributes green fruit and

liquorice aroma notes (Moyano et al., 2002). The latter

is a lactone resulting from the reaction between a-ke-tobutyric acid and acetaldehyde, which takes place

through the mechanism proposed by Pham, Guichard,Schlich, and Charpentier (1995). A number of authors

attribute a high odour impact to this compound, with

nut, curry and candy cotton notes in both sherry bio-

logical aged wines and others produced under oxidative

ageing conditions (Cutzach, Chatonnet, & Dubourdieu,

2000; Escudero & Etievant, 1999; Kotseridis & Baumes,

2000; Lopez, Ferreira, Hernandez, & Cacho, 1999).

On the other hand, Z-whisky lactone, also known aswood lactone, contributes vanilla notes, and the volatile

phenol eugenol spice aromas of clove. Both compounds

originate from precursors extracted by ethanol from the

casks and their concentrations increase with increasing

wine wood contact time (Maga, 1996; Perez-Coello,

Sanz, & Cabezudo, 1997; Singleton, 1995). The influence

of the compounds contributed by the cask wood was

clearly shown in a recent study by Moyano et al. (2002)on the odour series in fino wines.

Finally, ethyl isobutanoate, butanoate and hexanoate

(which contribute fruity notes to the aroma of wine),

and isoamyl alcohols and methionol (with no pleasant

individual odours), are produced mainly during the

alcoholic fermentation by yeasts, the former via esterase

activity and aminoacid metabolism the latter. It is

therefore difficult to relate clearly the observed changesin these compounds during biological ageing to flor

yeasts metabolism or the extraction of specific com-

pounds from the wood. Certainly the flor yeasts can play

a role in these changes, although alternative phenomena

such as esterifications (whether chemical or enzymatic),

and concentration effects caused by water evaporation

in the casks should not be discarded (Etievant, 1991;

Martinez de la Ossa, Perez, & Caro, 1987; Plata, Mau-ricio, Millan, & Ortega, 1998).

In order to identify those compounds most strongly

influenced by the biological ageing process from among

the nine above-mentioned, a principal component

analysis using them as variables was performed, in this

way obtaining a first principal component (PC)

accounting for 93.12% of the overall variance, and

Table 1

Aroma compounds contents (mg/L) in sherry fino wine during biological ageing, correlation coefficient ðrÞ between aroma contents and ageing time,

and odour threshold (mg/L)

Aroma compound 1 year 3 years 5 years r Thresholda

Acetaldehyde 91.0± 6.8 245± 4 257±2 0.8963 10

Ethyl acetate 66.7± 7.2 85.5± 3.5 61.9± 4.3 )0.1788 7.5

1,1-Diethoxyethane nd 5.29± 1.26 9.90± 0.70 0.9854 1

Methanol 80.1± 4.2 71.2± 1.8 68.6± 1.6 )0.8655 668

Ethyl propanoate 0.091± 0.032 0.934± 0.098 1.29± 0.07 0.9667 5

Ethyl isobutanoate 0.038± 0.013 0.658± 0.068 1.04± 0.06 0.9853 0.015

Propyl acetate 0.044± 0.011 0.319± 0.048 0.331±0.026 0.8661 65

Butandione 0.122± 0.031 0.259± 0.039 0.053±0.004 )0.3188 0.1

Methyl butanoate 0.184± 0.070 1.07± 0.16 2.49± 0.11 0.9857 1

2-Butanol 0.224± 0.015 1.89± 0.50 4.32± 0.25 0.9820 1000

1-Propanol 34.8± 1.5 49.6± 0.82 71.5± 1.5 0.9913 830

Ethyl butanoate 0.161± 0.012 0.691± 0.184 1.49± 0.26 0.9574 0.020

Isobutanol 48.0± 2.2 66.2± 1.1 70.6± 0.2 0.9360 40

Isoamyl acetate 0.896± 0.035 nd 0.021±0.002 )0.8560 0.030

1-Butanol 2.66± 0.28 6.16± 0.55 0.608±0.049 )0.3633 820

Isoamyl alcohols 300± 9 357± 5 380±2 0.9628 30

Ethyl hexanoate 0.092± 0.008 0.111± 0.008 0.176±0.013 0.9309 0.005

p-Cymene nd 0.134± 0.015 0.033±0.007 0.2367 66

Ethyl pyruvate 0.083± 0.014 0.048± 0.001 0.015±0.001 )0.9724 100

Acetoin 9.48± 1.16 22.7± 9.1 33.9± 3.1 0.9081 30

Octanal nd 0.109± 0.019 0.156±0.008 0.9639 0.64

4-Methyl-1-pentanol nd 0.063± 0.013 0.105±0.035 0.9185 50

3-Methyl-1-pentanol nd 0.065± 0.014 0.108±0.036 0.9200 50

Ethyl lactate 81.6± 6.3 471± 34 440±4 0.8249 100

1-Hexanol 0.916± 0.080 0.534± 0.126 1.31± 0.17 0.4840 8

3-Ethoxy-1-propanol 0.327± 0.006 0.661± 0.227 nd 0.0115 50

Ethyl octanoate 0.181± 0.010 0.151± 0.067 0.335±0.085 0.6570 0.002

Isobutyl lactate nd 0.558± 0.010 1.50± 0.20 0.9783 340

Furfural nd 2.53± 0.20 4.08± 0.77 0.9665 15

Ethyl 3-hydroxybutanoate 0.203± 0.027 0.520± 0.036 0.950±0.030 0.9927 67

Benzaldehyde nd 0.043± 0.015 0.234±0.024 0.9315 5

1-Octanol 0.227± 0.005 0.028± 0.018 0.102±0.033 )0.6071 10

5-Methylfurfural nd 0.141± 0.018 0.086±0.065 0.5276 16

Isobutanoic acid 0.153± 0.001 0.525± 0.078 0.530±0.177 0.7737 20

c-Butyrolactone 12.8± 4.2 24.3± 2.9 15.6± 4.7 0.2676 100

Butanoic acid 0.870± 0.212 6.93± 0.26 1.42± 0.19 0.0819 10

Furfuryl alcohol 0.116± 0.013 0.386± 0.037 0.566±0.013 0.9877 15

3-Methylbutanoic acid 0.732± 0.059 0.295± 0.003 0.369±0.030 )0.7664 3

2,3-Butanediol 689± 59 1156± 57 1537± 127 0.9778 668

Diethyl succinate 14.4± 1.7 9.42± 0.47 11.0± 1.9 )0.5722 100

Methionol 0.522± 0.164 0.823± 0.082 3.73± 0.16 0.9025 0.5

1-Decanol nd 0.351± 0.033 0.420±0.064 0.9170 5

b-Citronellol nd 0.032± 0.003 0.038±0.006 0.9145 0.1

Phenethyl acetate 0.237± 0.041 0.039± 0.005 0.102±0.018 )0.6436 0.25

Hexanoic acid 1.74± 0.09 2.81± 0.22 3.35± 0.32 0.9462 3

Benzyl alcohol 0.091± 0.002 1.83± 0.11 3.97± 0.16 0.9966 900

Phenethyl alcohol 52.0± 5.4 60.4± 1.1 64.1± 3.7 0.8289 10

Z-Whisky lactone nd 0.068± 0.003 0.181±0.003 0.9893 0.035

Pantolactone 0.642± 0.117 3.79± 0.09 4.44± 1.01 0.8973 500

4-Ethylguaiacol 0.199± 0.082 0.143± 0.032 0.149±0.032 )0.3998 0.046

Diethyl malate 4.29± 0.43 1.88± 0.09 2.18± 0.07 )0.7878 760

Z-Nerolidol 0.206± 0.015 0.096± 0.002 0.120±0.005 )0.7316 64

Ethyl myristate 0.215± 0.034 0.127± 0.016 0.051±0.007 )0.9648 494

Octanoic acid 0.810± 0.117 1.19± 0.06 1.01± 0.13 0.4473 8.8

c-Decalactone 0.167± 0.016 0.379± 0.107 0.748±0.188 0.9092 1

Eugenol 0.123± 0.015 0.163± 0.010 0.440±0.026 0.9130 0.005

4-Ethylphenol 0.067± 0.013 0.067± 0.009 0.066±0.006 )0.0173 140

Decanoic acid 0.560± 0.093 0.091± 0.009 0.093±0.012 )0.8472 15

Phenethyl octanoate nd 0.217± 0.088 0.031±0.011 0.1226 10

Monoethyl succinate 340± 69 209± 12 340±6 0.0000 1000

Lauric acid 0.052± 0.010 0.143± 0.008 0.143±0.002 0.8554 10

336 J.A. Moreno et al. / Food Control 16 (2005) 333–338

Table 1 (continued)

Aroma compound 1 year 3 years 5 years r Thresholda

Sotolon nd 0.072± 0.007 0.191± 0.025 0.9777 0.005

Ethyl furoate nd 0.024± 0.003 0.026± 0.007 0.8663 1

nd¼ not detected.aDetermined in 14% ethanolic solution.

Fig. 2. Odour activity values for Z-whisky lactone as a function of the

ageing time.

J.A. Moreno et al. / Food Control 16 (2005) 333–338 337

therefore it explained most of the variability in the

process. All nine variables exhibited a similar statistical

weight to this PC (between 0.3294 and 0.3450), with a

slight predominance of Z-whisky lactone (0.3450), sot-

olon (0.3397) and 1,1-diethoxyethane (0.3354). It is

interesting to point out that the concentrations of these

three compounds were below their GC detection limits

in the samples corresponding to 1 year (0.023, 1.47 and92.6 lg/L, respectively). This suggests that they were

synthesized exclusively during the process and thereby

they are valuable for their use as markers of the bio-

logical ageing.

Figs. 1–3 show the OAVs for sotolon, Z-whisky lac-

tone and 1,1-diethoxyethane, respectively, as a function

of the ageing time. Based on the value of r-squared, thelinear model accounts for over 95% of the variability inthe data for the three compounds. Because a compound

with an OAV higher than unity contributes with its

particular odour, the whole zone enclosed by the fitted

curve and the horizontal line at OAV¼ 1 can be adopted

as the odour activity region for each compound during

the biological ageing process. Thus, the area of such a

region indicates the total aroma production of each

compound throughout the process. Therefore, in aro-matic terms, sotolon with 69.2 area units would be a

good descriptor of the biological ageing, followed by

1,1-diethoxyethane and Z-whisky lactone (with 16.2 and

6.3 area units, respectively).

As above-mentioned, the compounds present at

concentrations below their perception threshold in the

Fig. 1. Odour activity values for sotolon as a function of the ageing

time.

Fig. 3. Odour activity values for 1,1-diethoxyethane as a function of

the ageing time.

wine cannot be considered key substances or markers

for biological ageing. However, their contribution to

the aroma (particularly in the case of compounds withnear-unity OAVs) cannot be ignored, because they can

enhance some existing notes by synergy with other

compounds (Freitas, Ramalho, Azevedo, & Macedo,

1999; Lopez et al., 1999).

In conclusion, based on their high odour impact and

on the highly linear relationship between their contents

(or OAVs) and the ageing time, sotolon, 1,1-diethoxye-

thane and Z-whisky lactone can be used as analyticalmarkers of the changes in fino wine during its biological

338 J.A. Moreno et al. / Food Control 16 (2005) 333–338

ageing, simultaneously considering their odour contri-bution to the sensory profile of this type of wine. These

compounds allow more accurately to determine the de-

gree of biological ageing in relation to its time of

duration, with a view to ensuring maximal uniformity in

the commercial product, independently of environmen-

tal factors of cellars and small differences in the sherry

winemaking techniques.

Acknowledgement

This work was supported by a grant from the MCYT

(AGL2002-04154-CO2-02) of the Spanish Government.

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