Pissarra JSFA 2005 Aldehydes in Brandies

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Journal of the Science of Food and Agriculture J Sci Food Agric85:1091 1097 (2005)DOI: 10.1002/jsfa.2070

Contribution and importance of wine spiritto the port wine final qualityinitial approach

Joao Pissarra,1

Sandra Lourenco,1

Jos e Maria Machado,2

Nuno Mateus,1

David Guimaraens2 and Victor de Freitas1

1Faculdade de Ciencias, Universidade do Porto, Departamento de Qumica, Centro de Investigac ao em Qumica, Rua do Campo Alegre,

687-4169-007 Porto, Portugal2The Fladgate Partnership, Vila Nova de Gaia, Portugal

Abstract: The commercial wine spirit used for this study revealed that the aldehyde content

mainly comprises acetaldehyde but other aldehydes such as propionaldehyde, 2-methylbutyraldehyde,

isovaleraldehyde, methylglyoxal, benzaldehyde and others are also present in significant amounts. A

typical grape must was used to assess the influence of wine spirit in the analytical and sensorial

characteristics of fortified wines. Decreasing levels of anthocyanins, as well the increase in the red

colour and tanning capacity, were observed, and seem to be positively correlated with the increase of

the aldehyde content present in the wine spirits used to fortify the must. Using the CIE L

a

b

system,this aldehyde content present in the spirit used seemed to be correlated with the decrease of the wines

lightness (darkening effect), the displacement of the hue angle to higher values (yellowing effect) and the

increase of the chromaticity (colour saturation) of the wines.

2005 Society of Chemical Industry

Keywords:ageing; wine colour; aldehyde; wine spirit; fortified wine; quality

INTRODUCTION

In port wine-making, when about half of the original

sugar content has been converted into alcohol, the

fermentation is stopped by addition of wine spirit(ratio wine/spirit 5:1, v/v). The quality of the

spirit is determined by its analytical and sensorial

characteristics, and for each vintage several wine spirits

commercially available are chosen by the port wine-

makers, taking into account their aroma quality as well

as their price. The aroma of the spirit is related to its

composition in different groups of compounds such as

higher alcohols, esters and aldehydes.1 The aldehyde

content present in wine spirit depends not only on

the original wine quality but also on the distillation

process.

Besides a little data about some aromatic com-pounds present in wine spirits used for the fortification

of port wines, there is practically no available infor-

mation concerning the aldehyde composition of these

wine spirits. Studies performed by Vanderlinde2 with

spirits used in the production of Cognac, Armagnac

and brandies revealed that acetaldehyde, formalde-

hyde, isovaleraldehyde, propionaldehyde, benzalde-

hyde, isobutyraldehyde and 2-methylbutyraldehyde

were the most abundant aldehydes. Aldehydes such as

methylglyoxal, glyoxal and others could also be present

in some wine spirits but only in trace amounts. Appart

from benzaldehyde, which has a pleasant bitter almond

aroma, all the aldehydes studied (acetaldehyde, pro-pionaldehyde, 2-methylbutyraldehyde, isovaleralde-

hyde, methylglyoxal, formaldehyde and isobutyralde-

hyde) have an unpleasant aroma (green leaves, bitter,

unripe fruit) that could contribute negatively to the

port wine aroma.

These aldehydes, and especially acetaldehyde,

interact with anthocyanins and flavanols, changing

the red wine colour. The contribution of acetaldehyde

in the tannin polymerization and copolymerization

between flavanols and anthocyanins has been widely

reported in the literature.3 6

These phenomena contribute to the colour changefrom red towards tawny that occurs during storage and

ageing (increase in colour intensity and a shift from

bright red to reddish-brown hues), which is attributed

to the progressive displacement of anthocyanins by

more stable complex pigments.514

In this work, a grape must was fortified with

ethanol (77% v/v) and with five commercial wine

spirits commonly used in port wine-making. The assay

of its composition in flavan-3-ol, anthocyanins and

Correspondence to: Victor de Freitas, Faculdade de Ciencias, Universidade do Porto, Departamento de Qumica, Centro de Investigacao

em Qumica, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal

E-mail: [email protected]/grant sponsor: FCT; contract/grant number: PRAXIS BD/16195/98

Contract/grant sponsor: Minist erio da Agriculture; contract/grant number: PO.AGRO 265

(Received 6 April 2004; revised version received 23 August 2004; accepted 1 September 2004)

Published online 26 January 2005

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colourimetric measurements was regularly performed

during 20 months of bottle ageing.

MATERIALS AND METHODS

Port wine-making and wine samples

The wine-making was conducted in a 200 hL stainless

steel contains from the 2001 vintage (from sub-regionBaixo Corgo in northern Portugal and with typical

blending of most abundant grape varieties) using

usual port wine-making techniques. Several aliquots

of the grape must were used for fortification with five

different commercial wine spirits (marked 15). A

reference test was made, replacing the commercial

wine spirit by ethanol 77% (v/v; marked 0). The

final alcohol content was set to 19% (v/v), and pH

and SO2 levels were initially adjusted for all samples.

During the maturation period, regular analyses were

performed and both pH and SO2 levels were kept

constant at similar levels for all samples. The samples

were bottled after 6 months and kept in a dark and

cool environment until further use.

Wine spirit analysis

Individual aldehyde composition of commercial wine

spirit was determined according to the relative abun-

dance of each aldehyde. Acetaldehyde was deter-

mined by GC-FID analysis, and propionaldehyde,

2-methylbutyraldehyde, isovaleraldehyde, methylgly-

oxal and benzaldehyde were determined by GC-MS

analysis.2

Acetaldehyde measurement by GC-FID analysisA volume of 10l of the internal standard solution

of methyl acetate (1.23 mM; Merck) was added to

1 ml of wine spirit. A volume of 2 l of this solution

was directly injected in a Varian Star 3400 CX gas

chromatograph with a flame ionization detector (FID).

The gas chromatograph was equipped with a Varian

CP Wax 52CB WCOT fused silica capillary column

(60m 0.25 mm id, film thickness= 0.50m). The

injector (split/splitless 45 s) temperature was set at

220 C and the flame ionization detector temperature

was set at 250 C. The carrier gas was helium (at a

flow of 1.0 ml min1

) and air, hydrogen and heliummake-up flow rates were respectively 300, 30 and

3 ml min1. The oven temperature was programmed

as follows: 40 C for 5 min; from 40 to 200C at

3.0 C min1; finally isothermal at 200 C for 20 min.

A linear calibration curve was established using

standard model solutions of acetaldehyde.

GC-MS analysis of less abundant aldehydes

The method used for aldehyde determination in wine

spirit was based on aldehyde determination in wines

as described by De Revel and Bertrand.15 Owing

to the strong aldehyde polarity, the low molecular

mass compounds are very difficult to quantify using

chromatography, so the use of derivatization agents

is needed as they produce condensed compounds,

oxymes, with aldehydes, which are easily detected as

they have a detection limit of few mg l1.

A 20ml aliquot of distilled water was added to 20ml

of wine spirit, 50 l of dodecanal (internal standard at

200mgl1, Aldrich) and 1 mlof PFBOA [O-(2,3, 4,5,

6-pentafluorobenzyl) hydroxylamine, derivating agent

at 12gl1; Fluka Chemica] and left to react for 1 h

at room temperature. The mixture was then saturatedwith 7 g of NaCl and followed by three extractions with

an etherhexane solution (4 + 2+ 2 ml) according to

the procedure reported elsewhere.2 The extract was

saturated with Na2SO4 anhydrous (Merck) and a

volume of 2l was set for injection in a Saturn

II (Varian) ion trap mass spectrometer (multiplier

voltage, 2550 V; emission current, 10 A; scan rate,

100scan min1; detector temperature, 170 C; mass

range m/z, 30250) coupled with a Varian 3400

gas chromatograph, equipped with a Supelcowax

10 fused silica capillary column (60 m 0.25 mm id,

film thickness = 0.25m). The oven temperature was

programmed as follows: 20 min at 40 C; 40200 C

for 32min; 200250 C for 5 min; 60 min at 250 C.

The helium gas flow was set at 1 ml min1.

The injector was programmed as follows: 120 C

for 0.1 min; 180C min1 until 250 C; 18.9min at

250 C; finally isothermal at 120 C. Injection volume

was 2l.

Individual aldehydes were quantified by comparing

the intensity of the corresponding molecular peaks

with that of the internal standard dodecanal. Linear

calibration curves were established for each aldehyde

based on the ion peak areas for standard solutions

submitted to the same analysis procedure.

HPLC analysis of anthocyanins

Samples were analysed by HPLC (Knauer, K-

1001) using a C18 column (250 4.6 m m id)

thermostatted at 25 C and detection was carried

out at 520 nm using a DAD detector (Knauer, K-

2800). Solvents were (A) H2O/HCOOH (9:1, w/w),

and (B) CH3CN/H2O/HCOOH (3:6:1, w/w). The

elution gradient was 20 85% B for 70 min, 85 100%

B for 5 min and then isocratic for 10 min at a flow rate

of 1.0 ml min1 according to the procedure described

in the literature.7 The anthocyanin 3-glucosides and

respective acylated esters were identified on the basisof their UVvis spectra and retention times by

comparison with standards. Calibration curves were

used to quantify all the anthocyanins glucoside and

acylated esters and the results are expressed in mg of

malvidin 3-glucoside (Mv3gl) per litre of wine.

Red colour evaluation

The contribution of total anthocyanins for the

relative red colour of wines was evaluated directly

by spectrophotometry at 520nm using a Shimadzu

spectrophotometer (UV-265) and a 1 mm quartz cell.

Lab colour measurements

Spectral transmittance curves were recorded from

360 to 830nm with a 1 nm sampling interval, using

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Contribution of wine spirit to port wine quality

a 2 mm pathlength cell and a UV-3101 Shimadzu

spectrophotometer. The colour coordinates were

determined in the CIELAB colour space using

CIE D65/10 illuminant/observer conditions. All the

colour calculations were performed using a computer

program developed at the Department of Physics of

Porto University. Tristimulus values were used to

calculate the CIE L

a

b

coordinates (a

, b

andL). The colour psychophysical parameters chroma

(C) and hue angle (ha,b) were obtained by the

transformation of the Cartesian coordinates (a and

b) to polar coordinates (C andha,b), according to the

described in literature.16,17

To allow a better correlation between visual and

colorimetric differences, the colorimetric difference

E and its components L, C and H for

each sample pair [sample and reference (with ethanol

fortification)] were determined according to Gonnet.16

From the spectral transmittance curves, a set of

tristimulus values (X,Y andZ) was computerized for

each illuminant/observer condition, and the Lab

coordinates determined according to Gonnet.16 L

means lightness to darkness (+L or L); +a redness

to greenness a; +byellowness to blueness b. Other

parameters were C, chroma, ranging from neutral

to fully saturated colour (+C or C), and h, the

hue angle of colour change around the colour circle

(+h or h). The CIELAB measurement showed that

colour intensity was an ambiguous term for product

colour, since it indistinctly covered simultaneous or

alternate variations of two colour attributes (lightness

and chroma), which differently influenced colour

appreciation.18 The colour difference or colorimetricdifference, E, reveals the changes in all colorimetric

parameters such as chroma, lightness and tonality, and

a mean threshold value ofE 1 was assumed as

a basis for perceptible colour differences between two

solutions.17,18

Polyphenol molecular weight index

Wine (5 ml) was introduced into a dialysis tubing

(cellulose; 6 mm id; nominal molecular weight cut-

offs of 12 000 16 000; average porous radius of 25 A)

and placed into a vial with 50 ml of synthetic solution

(12% aqueous ethanol, 5 g l

1 tartaric acid, pH 3.2).In the second vial 5 ml of wine was diluted directly

with the same hydroalcoholic solution up to 50 ml

(reference solution, do). Both vials were closed and

stored at room temperature for 24 h, and the dialysis

index was determined [PDI = (do d)/do] according

to the procedure described in the literature.19

Tannin-specific activity

The tannin-specific activity (TSA), as reported

elsewhere,19 was assessed using nephelometric pro-

cedures already described in literature using a HACH

2100N Turbidimeter.20 The fortified wine was diluted

to 1:50 with synthetic solution (12% aqueous ethanol,

5 g l1 tartaric acid and pH 3.2) previously filtered

(0.45m). A 150 l aliquot of bovine serum albumin

solution (BSA) was added to 4 ml of the wine solution

in a test tube. The mixture was then shaken and stored

at room temperature for 40 min. Wine tannins bind

with BSA to form insoluble complexes. This haze for-

mation of the solution increased with time, and after

40 min the formation of the complexes stopped and

the haze stabilized. The tannin-specific activity was

expressed in Nephelos turbidity units (NTU) per litreof wine.

Statistical analysis

All samples were analysed in triplicate. Analysis of

standard deviation was performed for every mean.

The analysis of variance by ANOVA tests was

also performed in order to test the effect of each

treatment. Differences were considered significant

when p < 0.05.

RESULTS AND DISCUSSIONPolyphenolic characterization of fortified wine

samples

After 6 months of bottle ageing, the composition of

anthocyanidin monoglucosides (AMG) and flavan-3-

ol oligomers of the fortified wine samples showed

some differences depending on the wine spirit used

(Table 1). The AMG content of these wines was

within a range of 220 440mg l1. The fortified wine

W5 showed the lowest AMG content (221.7 m g l1)

and the wine fortified with ethanol (W0) revealed

the highest anthocyanin content. These contents were

shown to be statistically different at the p < 0.01 leveland this outcome raised the possibility of the influence

of the wine spirit composition on the interactions

involving these pigments.

Table 1.Polyphenolic characterization of the sample wines fortified with five wine spirits (1 5) and ethanol (0) at 77% (v/v) after 6 months of bottle

ageing. The content of AMG (anthocyanin monoglucoside and acylated esters) is expressed in mg Mv3gl per litre of wine

Fortified wine

Phenolic characterization W0 W1 W2 W3 W4 W5

AMG (mg l1)a 437.3 21.8 313.3 15.7 293.1 14.7 391.1 19.6 325.7 16.3 221.7 11.1

Flavan-3-ols oligomers (mg l1)b 621.51 49.7 645.94 51.7 529.05 42.3 589.28 47.1 473.03 37.8 420.76 33.7

Red colour A520c 0.348 0.01 0.364 0.01 0.405 0.011 0.367 0.01 0.369 0.01 0.458 0.012

All samples were analysed in triplicate. Linear regression curves were used and analysis of SD was performed for every mean. Variance analysis by

ANOVA was performed.a p< 0.01; b p< 0.05; c p< 0.001.

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Similarly, the flavanol oligomers content for these

treatments showed statistically significant differences

between all samples at the p< 0.05 level. The port

wine W5 also revealed the lowest level (420 mg l1),

whilst the higher flavanol content was found in samples

W0 and W1 (621 and 645 mg l1, respectively),

and the flavanol content of the remaining samples

was between these two levels. The evaluation ofthe red colour (Abs520 nm) revealed that the lowest

polyphenolic content corresponded to a more reddish

and darker sample (W5 with higher absorbance values)

and the ethanol sample (W0) had lower red colour

intensity and was also less dark. All the other sample

parameters were found to be between these two levels

and these differences were shown to be significantly

important at the p < 0.001 level.

Effectively, these wine samples showed significant

differences at thep < 0.05 level in all the polyphenolic

parameters studied, suggesting that the wine spirit

composition might be an important factor concerning

the colour contribution and its stabilization.

Among the several group of compounds reported to

occur in wine spirits1 (alcohols, esters and aldehydes),

aldehydes and especially acetaldehyde have been

described in literature to be reactive with anthocyanins

and flavanols, leading to taste and colour changes.3 6

Thus, the aldehyde composition of these five wine

spirits was assessed (Table 2). Acetaldehyde was found

to be responsible for almost the total aldehyde content,

whilst the other aldehydes were present in different

relative amounts. Indeed for spirit 5, acetaldehyde

was responsible for 87.5% of total aldehydes and for

more than 92.5% in the other spirits (14). On theother hand, spirit 5 contains a much higher amount

of aldehydes, almost 4.6 times superior than the spirit

with the lowest aldehyde content (1).

Since the AMG and flavanol oligomers content

seemed to decrease proportionally with the increase

of the aldehyde content present in the wine spirit,

reactions involving aldehydes, AMG and flavanols are

thought to occur. Effectively, the aldehydes identified

in the wine spirits were already shown to be able

to react with anthocyanins (malvidin 3-glucoside)

and flavanols [(+)-catechin (cat)] in model solutions

(conditions similar to the wine) to form new coloured

pigments.17 These newly formed pigments were

identified as being mv3gl and cat adducts linked by an

alkyl/aryl bridge and their maxin the UVvis spectrum

revealed a bathchromic shift when comparing with that

of original anthocyanins.17

Apart from the ethyl linked adducts resultingfrom the reaction of mv3gl and cat mediated by

acetaldehyde, the other alkyl/aryl adducts have never

been reported in wines, mainly due to the low

aldehyde concentration. In addition, these ethyl linked

adducts are supposed to be unstable in wines and

to be more likely intermediates for the formation of

pyranoanthocyaninflavanol pigments.21,22

The evolution of the AMG content and the red

colour evaluation was followed during 20 months of

bottle ageing (Figs 1 and 2). The ageing period led

to a decrease in the AMG content to levels below

100mgl1 for all wine samples, as well as an increase

in the red colour parameter. During this period,

the relative order of these two parameters in wines

remained constant. Effectively, sample W5 kept the

lowest AMG content and higher red colour intensity,

while sample W0 kept the highest AMG content

and the lowest red colour intensity. The remaining

Table 2.Aldehyde composition of 5 commercial wine spirits used in

port wine-making. Formaldehyde and isobutyraldehyde were not

detected in these wine spirits

Wine

spirits A P 2MB IV MG B Total (mg l1)

1 42.38 ND 2.54 0.26 0.42 0.16 45.76

2 74.14 ND 0.41 0.17 0.61 0.02 75.35

3 52.90 ND 0.69 0.81 0.90 0.23 55.53

4 70.08 ND 0.86 0.74 1.47 0.69 73.84

5 185.71 0.22 5.69 4.14 16.34 0.08 212.18

Legend: ND, not detected.

All samples were analysed in triplicate. Linear regression curves were

used, analysis of standard deviation was performed for every mean.

A, acetaldehyde; P, propionaldehyde; 2MB, 2-methylbutyraldehyde;

IV, isovaleraldehyde; MG, methylglyoxal; and B, benzaldehyde

AMG

0

100

200

300

400

500

5 7 9 11 13 15 17 19 21

Months of ageing

Concentration

(expressedinmgMv3glper

liter)

0

1

2

3

4

5

Figure 1. Evolution of the AMG content present in the wine samples fortified with five wine spirits (15) and ethanol (0) after 6, 10, 15 and

20 months of bottle ageing.

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Red Colour evaluation

0.3

0.4

0.5

5 10 15 20

Months of ageing

Absorbance

(

Abs520)

01

2

3

4

5

Figure 2. Evolution of the red colour evaluation of the wine samples fortified with five wine spirits (15) and ethanol (0) after 6, 10, 15 and

20 months of bottle ageing.

samples showed levels between these two. Further

colourimetric discussion will be given in more detail

in theLab discussion.

After 20 months of bottle ageing, the wine samples

showed significant differences at the p< 0.001 level

in their molecular structure complexity. Indeed, the

wine polyphenol average molecular weight was shown

to have a slight tendency to increase in the samples

made with spirit with higher levels of aldehydes

(Table 3), especially sample W5, which presents

a higher aldehyde content. This outcome was in

agreement with the tannins ability (present in wines)

to react with BSA to form insoluble aggregates,

inducing higher TSA values (Table 3). The TSA

allows characterization of the reactivity of different

polyphenols towards proteins.20,23 BSA has been oftenused as a model protein to study the interactions

between polyphenols and proteins, simulating the

phenomena between tannins with salivary proteins

occurring in mouth and responsible for the astringency

sensation. Previous studies had already shown that the

TSA tended to increase with the polyphenol molecular

weight.20,23 The TSA of all treatments evidenced some

differences, but they were not found to be significantly

different (p< 0.1).

Despite not being an initial purpose of this work,

a sensorial evaluation of these wines was performed

Table 3.Polyphenol molecular weight index and tanning capacity

characterization of the wine samples fortified with five wine spirits

(1 5) and ethanol (0) after 20months of bottle ageing

Fortified wine

Polyphenol MW

index (%)aTanning capacity

(NTUml1)b

W0 27.8 0.4 32.1 0.4

W1 24.4 0.1 32.5 0.4

W2 30.5 0.5 41.7 0.4

W3 32.5 0.1 36.3 0.4

W4 29.3 0.2 38.8 0.4

W5 36.5 0.8 39.2 0.4

All samples were analysed in triplicate and the analysis of SD

was performed for every mean. Variance analysis by ANOVA was

performed.a p< 0.001; b p< 0.1.

by a taste panel composed by 11 panelists with much

experience in port wine tasting. These wines showed

slight differences. Samples W5 and W4 revealed a

more intense colour and taste. The latter probably

resulted from the higher tannin reactivity toward

salivary proteins. Sample W3 showed the opposite

flavour sensation (data not shown).

All these parameters suggest a possible correlation

between the aldehyde content and some organoleptical

properties of these wine samples.

Table 4.Colorimetric characterization after 6, 10, 15 and 20 months

of bottle ageing of the sample wines fortified with ethanol (0) and five

wine spirits (15). The colour parameters were determined for eachsample pairwine spirit (15) and ethanol fortification (0)

Ageing time (months in bottle)

Wine Colour

spirit parameters 6 10 15 20

0 L 66.57 66.74 64.67 63.70

a 36.98 34.35 36.75 36.99

b 1.26 3.46 6.27 6.02

1 C 0.44 1.37 1.18 0.71

H 0.19 0.30 1.54 0.23

L 1.12 1.93 2.31 1.76

E 1.22 2.38 3.02 1.91

2 C 2.42 3.63 1.87 1.90

H 0.09 0.30 1.93 1.08

L 3.88 5.61 3.89 4.43

E 4.57 6.69 4.73 4.94

3 C 0.37 1.10 1.30 0.72

H 0.54 0.13 1.13 0.02

L 1.52 2.03 3.33 2.04

E 1.66 2.31 3.75 2.16

4 C 1.81 3.72 1.76 1.31

H 0.59 0.27 1.20 0.35

L 2.96 4.75 4.97 4.17

E 3.52 5.47 5.41 4.39

5 C 4.87 3.72 2.81 1.53

H 0.80 0.27 1.84 1.15

L 7.07 7.22 8.04 6.32E 8.63 8.13 8.72 6.61

All samples were analysed in triplicate.

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Chromatic analyses

The wine samples were submitted to chromatic

analysis as described in the Materials and Methods

and the results obtained are summarized in Table 4.

The analysis after 6 months of bottle ageing showed

that the wine samples fortified with the spirit with

higher aldehyde content revealed higher lightness

parameter changes (L

= 7.07, 3.88, 2.96,1.52 and 1.12 for wines W5, W2, W4, W3 and

W1 respectively), meaning a darkening effect on the

wine samples. The wine samples were also found to

have consistent variations in the hue angle (H) and

in the chroma (C). Indeed, in the wine samples with

higher aldehyde content, the hue angle was displaced

to higher values (H = 0.54, 0.19, 0.09, 0.59

and 0.80 for wines W3, W1, W2, W4 and W5,

respectively), meaning that the tonality of each wine

suffered a displacement into red yellowish hues or

showing a yellowing effect. The chroma variation

reflects a change to a more saturated colour of the

wines when they are fortified with higher aldehyde

content present in the respective spirit (C = 0.37,

0.44, 1.81, 2.42 and 4.87 for wines 3, 1, 4, 2

and 5 respectively). All these colorimetric changes

can be easily evaluated by the analysis of E,

the colorimetric difference parameter. Higher E

values mean stronger colour effects, which can be

represented, in CIE Lab three-dimensional space

by the distance between the two sample points (sample

and reference). All these wine samples, after 6 months

of ageing, revealed perceptible colour differences as

all of them revealed a E >1.16,17 Despite slight

differences, this behaviour seemed to be constant forall samples and during the 20 months, revealing that

the chemical composition of the wine spirits used, and

more probably their aldehyde content, led to changes

in the colorimetric feature of the respective wine.

Smaller colorimetric differences (lowerE values)

were found in the wines with high phenolic content

(data not shown), suggesting that the correct choice

of the spirit to use in port wine-making could be a

powerful tool in enhancing colorimetric characteristics

of some port wines.

CONCLUSION

Concerning the process of port red wine ageing, the

role of the aldehyde composition of the wine spirit used

for fortification of the musts was here focused on for

the first time and seems to be important in achieving

better sensorial properties of red port wine. Indeed, the

wine sample fortified with the wine spirit with higher

aldehyde content was shown to have a more intense

colour and taste, which are two important sensorial

factors in the port wine industry.

Thus, not only grapes and must composition (allied

to climate factors, viticulture practices and terroir

characteristics), but also the wine spirit quality used

in port wine-making (and other enological practices),

are powerful tools to improve port wine quality.

ACKNOWLEDGEMENTS

This research was supported by a grant from FCT

(Fundacao para a Ciencia e Tecnologia PRAXIS

BD/16195/98) and from the Ministerio da Agricultura

(PO.AGRO 265), both from Portugal.

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