Characterization of aged champagne wine aroma by GC-O and descriptive profile analyses
Ana ESCUDERO * 1, Monique CHARPENTIER 3, Patrick ETIEVANT 2
RÉSUMÉ Caractérisation par analyse sensorielle et GC-O de l’arôme du champagne en vieillissement normal et en vieillissement accéléré.
Le but du travail est de caractériser l’évolution de l’arôme du champagne au cours du vieillissement et de comparer sous ce rapport le vieillissement accé- léré à 40 ºC au vieillissement normal. Les méthodes mises en œuvre à cet effet sont l’analyse sensorielle, et les techniques GC-O et GC-MS. La représentati- vité des extraits a été étudiée au préalable par tests triangulaires et tests de similarité. Les profils descriptifs ont été établis par un panel d’experts sur des échantillons jeunes et vieillis. L’intensité des notes florale et fruitée diminue au cours du vieillissement, celles des notes boisée et d’évolution augmentent. On observe cependant des différences sensorielles entre les produits des deux types de vieillissement. La technique de GC-O montre que le vieillissement normal met en jeu trois processus : la réaction de Strecker qui produit du 3- (méthylthio)-1-propanal et furanéol d’éthyle à partir des acides aminés, la for- mation d’eugénol, et l’oxydation de composés d’arôme très sensibles tels que le furanéol. En revanche, ces trois réactions sont moins importantes dans le vieillissement accéléré, qui fait intervenir surtout quatre autres réactions : la dégradation d’acides gras insaturés pour produire le cis-3-hexenol, la forma- tion de 2, 3-butanodione et de guaiacol, et le métabolisme de la phénylalanine en benzaldéhyde. Ainsi, bien qu’un certain nombre de réactions se retrouvent identiques dans les deux types de vieillissement, le chauffage du champagne ne conduit pas à des produits proches de ceux obtenus par vieillissement nor- mal.
Mots clés : champagne, vieillissement, vieillissement accéléré, GC-O, analyse sensorielle.
1. Department of Analytical Chemistry, Faculty of Sciences, University of Zaragoza, 50009 Zaragoza, Spain.
2. Laboratoire de recherches sur les arômes, Institut national de la recherche agronomique, 17 rue de Sully, 21034 Dijon cedex, France.
3. Moët & Chandon, 6 rue Croix de Bussy, 51200 Épernay, France.
* Correspondence [email protected]
SUMMARY
This paper aimed to characterise and compare the changes in champagne aroma with aging, in normal or accelerated conditions (at 40ºC), by sensory, GC-O and GC-MS analyses. Initially, extract representativeness was tested by triangle and similarity tests and descriptive profiles were established for young and aged samples by a expert panel. The intensity of floral and fruity notes were shown to decrease with aging. Oak and evolution characters increased, although there were some other sensory differences between the two aged products. GC-O differences could be related to several phenomena. Three pro- cesses were characteristic of normal aging: firstly, the Strecker reaction of amino acids to produce 3-(methylthio)-1-propanal and ethyl furaneol; secondly, the generation of eugenol, and thirdly, the oxidation of sensitive flavor com- pounds such as furaneol. Other processes were also characteristic of accelera- ted aging: the degradation of unsaturated fatty acids to form cis-3-hexenol; the formation of 2, 3-butanedione and guaiacol; and the metabolism of phenylala- nine to produce benzaldehyde. So, although common types of reactions were present in both aging methods we can conclude that champagne heating is not an aging method which is identical to the standard technological aging proce- dure.
Key-words: Champagne wine, aging, accelerated aging, GC-O, sensory analy- sis.
1 - INTRODUCTION
Champagne wine is a French wine produced from three different grape varieties: Pinot Noir, Pinot Meunier and Chardonnay. Organoleptically, the wines depend on the chemical composition of the initial must and fermentation condi- tions. In champagne wine, the second fermentation in the bottle and the aging on yeasts are both responsible for the typical characteristics; namely the color, the bouquet and the flavor.
Champagne aging involves a long period of contact in the bottle between the wine and the lees. The exchanges between wine and yeast cells, which lose their ability to reproduce at the end of the alcoholic fermentation, have often been considered as an important factor contributing to the organoleptic quality of sparkling wines (LOYAUX et al., 1981). It is recognised that during aging, yeast cells are autolysed and free amino acids are released into the medium. This phenomenon appears after some months of aging and may extend for some years. It is known that the aroma development during aging on yeasts is coupled to the biochemical mechanism of autolysis (FEUILLAT, 1980), but it is also thought that another phenomenon, oxidation, takes place during the same period.
In the literature, numerous studies concern the flavor changes during matu- ration of wines (DI STEFANO, 1985; CHISHOLMet al., 1995; MARAIS and POOL, 1980; USSEGLIO-TOMASSET, 1983; DI STEFANO and CASTINO, 1984; RAPP and MANDERY, 1986; SIMPSONand MILLER, 1984; LOYAUXet al., 1981; FERREIRAet al., 1997), and describe changes taking place in the concentration of volatile com- pounds. However a systematic study of champagne wine flavor due to aging on
yeasts has never been carried out by descriptive profile and Gas Chromatogra- phy Olfactometry (GC-O) analyses.
Aging studies are very expensive and for obvious reasons take a long time.
Accelerated agings are therefore used to simulate and accelerate this pheno- menon. Heating was the first technique used (RODOPOULO, 1965; SINGLETON and KRAMLING, 1976), although more recently electrochemical oxidation has been used to ensure the browning of sherry wines (PALMA LOVILLO, 1995).
During wine heating new oxidation-reduction systems of wine are responsible for the redox potential decreases which accelerate wine aging (RODOPOULO, 1965). The extent and nature of the changes (color and flavor) vary with the wine, the presence or absence of oxygen, and the time and temperatures of storage. Accelerated oxidation experiments at 55°C with oxygen have been conducted to follow wine browning, and good prediction of the browning of white wines was obtained (FERNANDEZet al., 1995). Other authors followed the aroma alteration at 50°C in the presence of air (SIMPSON, 1978) or at 40°C in the presence of nitrogen (DE LA PRESA-OWENSand NOBLE, 1997).
The heating of wines on yeasts quickly increases the nitrogen content of wine, but this transference phenomenon is passive. Nitrogen increase by autolysis the- refore is of another nature (FEUILLAT, 1980), and is in fact an enzymatic phenome- non in which temperature is an important factor, which increases the kinetics of autolysis and accelerates wine maturation (KORMAKOVA and DRBOGLAV, 1976).
Too high a temperature (> 50°C) however inhibits the proteolytic activity of yeast and of other enzymes due to thermal degradation (FEUILLAT, 1980).
In this study, an accelerated champagne aging process at 40°C for 30 days on yeasts was tested as a technique for acheiving an aged champagne aroma.
Sensory analyses were used to compare the aging to the standard technologi- cal procedure of aging (12°C in the cellar, for more than twenty years on yeasts).
2 - MATERIALS AND METHODS
2.1 Champagne wines
The reference (young champagne) was a vintage from 1996. This reference was heated for 30 days at 40°C (simulated old). Two other champagne samples were also analysed, one from 1994 (Ch2) and from 1975 (Ch21). Four Moët &
Chandon champagnes, all blendings of three grape varieties (Pinot Noir, Pinot Meunier and Chardonnay) were studied. The alcoholic content of the four wines was 12.5: 100 (v: v).
2.2 Extraction of odorous components
2.2.1 Demixtion and distillation
171 g of (NH4)2SO4, 41.85 g of H2NaPO4-H2O and a magnetic rod were suc- cessively added to a specially designed dry 500 mL flask, as described by MOIO
et al. (1995). The flask was then purged of oxygen by alternative connection to a vacuum pump, and to a nitrogen supply (99.995 purity) using a three way high vacuum glass tap. Next, 1 mL of a BHA solution (2 g·L–1in ethanol) was sucked into the flask under slight vacuum, as an antioxidant. The champagne sample (375 g, estimated by weighing) was then directly introduced from the bottle into the flask using an aphrometer (an instrument designed to measure the pressure in a bottle) connected to the extraction flask with teflon tubing (1/8 inch external diameter) tightened with Swagelock ferrules and knots, in order to avoid any contact of the champagne with oxygen. The wine sample was mixed with the salts and the ethanolic solution (antioxidant) until complete dissolution. The flask was then inverted for 1 h to allow phase separation. Air was then introdu- ced into the flask, the aqueous phase decanted and discarded, and the organic phase transferred into a small vial stored at – 20°C.
A two-stage distillation of these demixtion extracts was then performed to remove the non-volatile constituents (mainly pigments and salts). Firstly, 12 mL of the extract was distilled for 1.5 h under a pressure of 0.2 Pa as described by DUMONT and ADDA (1970). Secondly, the residue was further distilled on a cold finger (cooled by liquid nitrogen) for 1 h at 0.001 Pa, as described by RICHARDand ETIEVANT(1997). The condensate was rinsed from the cold finger with the distillate obtained from the first distillation, and this final extract was stored at – 20°C.
The extracts obtained from champagnes Ch2 and Ch21 (ext2 and ext21) were submitted to comparison tests, descriptive profiling and GC-O analyses.
Afterwards, the extracts obtained from the reference and the same champagne heated were compared.
2.2.2 Solvent extraction
The concentration factor of the volatile compounds in the final extracts (from 417 mL to 12 mL) was not high enough to allow their identification by GC-MS.
In order to facilitate these identifications, an aliquot of each extract was re- extracted with dichloromethane. Five mL of each extract in a 25 mL screw-cap- ped flask was diluted with 20 mL of the ammonium sulphate solution (263 g·L–1 (NH4)2SO4 in H2O (Milli Q)), and stirred with 0.5 mL CH2Cl2 for 30 min. After separation of the two phases, the organic layer was taken off with a syringe and transferred into a small vial, and then stored at – 20°C. A 1 µL aliquot of the organic layer was analysed by GC-MS equipment.
2.3 Gas-Chromatography
2.3.1 GC-O analyses
The analyses were carried out using a HEWLETT-PACKARD 5890 chromato- graph equipped with an on-column injector (J & W Scientific Inc.), a flame ioni- sation detector, a sniffing port, and a DB-Wax fused silica capillary column (30 cm, 0.32 mm i.d., film thickness 0.5µm, J & W Scientific Inc.) connected to the injector with a 5 cm deactivated polar pre-column (0.53 mm i.d., J & W Scientific Inc.). The column effluent was split equally between the detector and the sniffing port, and humid air (100 mL·min–1) was added to the sniffing port effluent. The hydrogen carrier gas velocity was 50 cm·s–1, and the temperature of the detector was set at 250°C. The oven temperature was programmed to increase from 67 to 240°C at 5°C·min–1.
A 5 µL aliquot of each extract was injected. During the analysis, FID and olfactometry signals were simultaneously recorded, using the hardware and the software developed by MIELLEand ALMANZA(1993). The linear retention indices of the FID and the olfactometry peaks were determined according to the method of VAN DEN DOOLand KRATZ(1963), using a C10 to C28 n-alkane solu- tion analysed once a day.
2.3.2 GC-MS analyses
GC-MS analysis was carried out on a HP 5970-quadrupole mass spectro- meter directly coupled to a HP 5890 gas chromatograph. The same column and pre-column used in GC-O experiments were coupled directly to the ion source (temperature 150°C). The carrier gas was helium, and the other conditions were identical to those described above. Electron impact mass spectra were produ- ced with an ion-source energy of 70 eV and a recorder with a HP-UX Chemsta- tion. The identifications made by MS were systematically confirmed with the retention indices of the pure references, determined under the same analysis conditions.
2.4 Sensory analyses
2.4.1 Comparison tests
The panel consisted of 28 subjects (18 men, 10 women, average age 37) from the internal panel of Moët & Chandon. They had been trained to work with dark glass screw-capped flasks with absorbent paper inside.
Aliquots of the wine extracts (50µL) were adsorbed onto 55 ×27 mm pieces of absorbent paper (OSI, type P110), and placed after 2 min (the time necessary for solvent evaporation) in 60 mL dark glass screw-capped flasks. For cham- pagne, 700µL of the wine was adsorbed onto the same support and placed in the same kind of flasks. For sensory evaluation, the panellists had to open the different coded flasks and to sniff the samples.
The impact of aging on the aroma of the champagnes and their extracts was assessed by triangle tests (AFNOR, 1983).
Two similarity tests were performed to compare the odor of the extracts (ext2 and ext21) with the odor of the extracted champagne wines (Ch2 and Ch21). First the champagne wine Ch2 was presented as the reference sample and the extracts were presented in a random order. The panel members were instructed to sniff and to memorise the aroma of the reference sample and then to sniff the first coded flask (containing one of the two extracts) and to deter- mine the similarity of their odors. A 100 mm unstructured scale was used for this, anchored with “identical to the reference sample” on the left and “different from the reference sample” on the right. The panellists were then asked to repeat the evaluation using the same reference sample and the second coded flask. The champagne wine Ch21, was then tested using the same protocol.
2.4.2 Descriptive profile analyses
The panel was the same as for the comparison tests, and had been trained to perform descriptive profile analyses on champagne wines. Champagne wine samples (10°C, 70 mL) were presented in coded glasses.
A list of 20 consensus descriptors previously established by the panel was used to describe the odors of the four wines. The order of the sample evaluation was randomised over all the subjects. The intensity of each of the twenty attri- butes was rated on a zero to six scale; a score of zero indicated that the des- criptor was not perceived, while a score of six indicated the highest intensity.
2.4.3 GC-O evaluation
The evaluations were made by nine assessors (5 women, 4 men, average age 33). These people were recruited from the population of Dijon, and they were paid. Seven of them had previous experience in this type of evaluation.
They were asked to sit in front of the sniffing port during the analysis (30 min), and to press the space bar on a computer keyboard when, and as long as, an odor was detected. Furthermore, they were asked to describe the quality of the odor detected, which was automatically recorded.
2.5 Data analyses
2.5.1 GC-O data
The data treatment is based on the detection frequency observed for each retention time (POLLIENet al., 1997). The nine individual aromagrams, produced for each extract, were first adjusted for slight retention index shifts, and then pooled into one aromagram by simple summation, and converted into a contin- gency table. A McNemar test was performed on each pair (Ch2/Ch21 and refe- rence/heated) to evaluate the aging effect, using the SigmaStat 2.0 Software.
These tests allowed a selection of those odors which were evaluated differently for the young champagne compared to the old one, at p < 0.08.
A factorial correspondence analysis (FCA with no rotation, StatBox 2.1 soft- ware, Grimmer logiciels, Paris) was then performed on the selected odors using the same data.
2.5.2 Comparison test and descriptive profile data
In the triangle tests, the number of total and correct answers were used to test, with a binomial law table set at 1/3 probability, if there were differences in the odors between the samples.
In the similarity tests, the marks on the unstructured scales were read as dis- tances in millimetres from the left hand side. A univariate analysis of the variance was carried out on these distances for the sample effect, to test the significance of the difference between the panel’s mean answers.
Univariate analyses of the variance (AOV) were performed on the data of descriptive profile analyses (mean values for each descriptor for the four samples) in order to identify the descriptors used by panellists to differentiate (at p < 0.05) the young and aged samples.
3 - RESULTS AND DISCUSSION
This paper focuses on the applicability of the GC-O method to differentiate the sensory characteristics of young and aged champagne wine aromas. A comparison between standard and accelerated aging was realised by GC-O and descriptive profiles.
Figure 1
Sensory profile of champagne wines (Ch2, Ch21, reference and heated)
# significant descriptor at p < 0.05 in the comparison of Ch2/Ch21.
* significant descriptor at p < 0.05 in the comparison of reference/heated.
The sensory difference among the samples due to aging was investigated by descriptive profile analyses of the four products. Figure 1 showed that the inten- sity of the “floral”, “citrus fruits” and “tree fruits” notes significantly decreased (p = 0.05) with both the accelerated and the standard aging, while descriptors associated with wine maturity, “wood”, “animal”, “moldy” and “cooked wine”,
increased with both aging conditions. Other authors (DE LA PRESA-OWENS and NOBLE, 1997) have also reported that the intensity of aromas associated with oak increased with aging whilst the intensity of floral and fruity notes decreased during accelerated aging. Some descriptors such as “cooked fruits”, “dried toasted fruits”, “coffee, caramel” and “dried grass” only increased significantly with standard aging, whilst “toasty” and “sulfur” notes only increased with accelerated aging, which indicates a difference between these two aging condi- tions. Consequently, the Ch21 (normally aged) and the heated profiles show a difference in the intensity of “cooked wine” descriptor, with the higher intensity unexpectedly being associated with normal aging. There were also sensory dif- ferences between the champagnes produced by the two aging methods.
Amongst the numerous possible extraction techniques described to isolate the flavor constituents of wines, we chose the demixtion technique followed by a distillation, since this method has been proved to give an extract with an odor descriptive profile for champagne which is closer to that of the original wine than the odor obtained with other techniques, (PRISER et al., 1997). To get reliable results, a protection of the flavor constituents was used; an antioxidant (BHA) was introduced before flavor extraction as recommended by ESCUDERO and ETIEVANT(1999).
Before testing the significance of the differences in the odor of extracts from different products, it was necessary to know if a difference actually existed bet- ween the two champagne wines, young (Ch2) and aged (Ch21), and their two extracts (ext2 and ext21).
The triangle tests obtained show that the odor of the two extracts and of the two champagne wines was significantly different with p < 0.001 (table 1).
Table 1
Triangle tests realized on wine extracts and on champagne wines
Pair tested Correct answers p value
versus total answers
ext2 and ext21 23/28 < 0.001
Ch2 and Ch21 25/28 < 0.001
Table 2
Similarity tests comparing the odor of champagnes to the extracts.
The data are the distance measured in mm (σn–1)
Sample evaluated Ext2 Ext21 p value
Ch2 40.4 (27.8) 66.5 (23.5) < 0.001
Ch21 56.6 (29.9) 36.4 (23.2) 0.008
Knowning this, two similarity tests were performed to check if the aroma of each extract resembled the champagne from which it was obtained more than the another extract. The results are shown in table 2. These tests demonstrated
that the mean estimated distances between the odor of the two extracts and the odor of the wines were not equal (p < 0.05, table 2). Consequently the aroma extracts were representative of the wine from which they were obtained.
In order to know more about the flavor active components characteristic of old champagne, a GC-O analysis was performed on four extracts made from Ch2, Ch21, champagne reference and champagne heated. The panel analysis, limited to 30 min, was described by ACREE, 1993. The analysis of the four final aromagrams obtained by summation of the individual sniffings showed that 88 different odors were detected by the panel.
Table 3
Characteristics of the 19 odors selected by two McNemar tests
LRI* Odor description p values MS Identification
Ch2/Ch21 refer./heated
982 strawberry and > 0.10 0.083 2,3-butanedione
cream sweet
1323 foot, bleach 0.083 > 0.10 3-methyl-1-butanol
1441 cut grass > 0.10 0.083 cis-3-hexenol
1495 caramel, cake shop 0.083 > 0.10 Not identified
1496 potato, yeast 0.083 > 0.10 3-(methylthio)-1-propanal
1549 potato, flower, fruit, aldehyde > 0.10 0.083 benzaldehyde
1705 flower, sweat, potato 0.083 > 0.10 diethyl succinate
1733 yeast, thiol, potato, 0.083 0.083 3-(methylthio)-1-propanol cut grass
1855 smoke, mint, > 0.10 0.083 guaiacol
toasted wood
2007 liquorice, 0.083 0.083 phenol
burnt wood
2023 wood, sugary, 0.046 0.083 Not identified
synthetic strawberry, almond
2031 caramel, 0.083 > 0.10 furaneol
toasted sugar
2090 strawberry, 0.025 > 0.10 ethyl furaneol
caramel, sugar
2109 skin, chemical, 0.025 > 0.10 Not identified
synthetic strawberry, caramel
2158 spicy, coffee, > 0.10 0.046 Not identified
food, plastic
2161 spicy, cloves 0.083 > 0.10 eugenol
2221 flower, skin, coffee 0.083 0.008 Not identified
2229 smoked ham, spicy, > 0.10 0.046 Not identified
burnt wood
2238 flower, sweet, 0.046 > 0.10 γ-undecalactone
vanilla
* LRI = Linear retention indices in Cwax.
Figure 2
Factorial correspondence analysis: relative positions of 4 samples and 19 odors in the plane formed by the first and the third axis
The odors are plotted with their LRI or their identification (see table 3).
In order to determine the differences which could be related to aging bet- ween aromagrams, two McNemar tests (χ2 analysis of the contingency table, AGRESTI, 1996) were applied. As a result 19 odors were detected with a signifi- cant frequency difference (p < 0.08) between the young and the aged extracts (table 3).
The descriptions of these 19 selected odors are also given in the same table, with their retention indices in Cwax and their identifications. Although our pane- lists were not trained to describe odors, the sensory terms of table 3 corres- pond roughly to the description expected for the compounds which were identified (by GC-MS with injection of pure substances), except for the odors at retention indexes of 1495, 2023, 2109, 2158, 2221 and 2229, for which no mass spectra could be obtained.
In order to obtain a general view of the GC-O odors which characterized the four extracts, a factorial correspondence analysis was made using the detection frequency of the 19 GC-O odors selected above. The most interesting informa- tion given by this analysis is seen on the plane formed by the first and the third axis as shown in figure 2. The first axis (48% of the information) mainly distin- guishes the extract of Ch21 from the rest of extracts whilst the third axis (20%
of the information) distinguishes the extract of Ch2 from the others. The second axis (31% of the information), not shown, distinguishes the two aged samples from the two young samples.
The difference between Ch21 and the other sample is due to a more fre- quent detection of ethyl furaneol, eugenol and the odor detected at LRI 1495, but also to a less frequent detection of guaiacol and of the odor at LRI 2221 (figure 1). As seen from the same figure, the extract Ch2 is characterized by a more frequent detection of odors at LRI 2109 and LRI 2158, and by a less fre- quent detection of 3-methyl-1-butanol, guaiacol and a compound at LRI 2229.
If one looks now at the differences between young and aged wines, some conclusions can be drawn.
The detection frequency and thus the concentration (POLLIENet al., 1997) of phenol (LRI 2007) is shown to decrease during aging. This compound can disappear in older wine due to oxidation, although this phenomenon is more often described for 1,2- and 1,4-diphenols (WILDENRADTand SINGLETON, 1974).
The “wood” and “animal” notes, which could be related to phenol, were stron- ger in the aged wines; hence, there is not a good ageement between the change of this compound with aging and the sensory profiles.
Diethyl succinate (LRI 1705) was detected more often in the young cham- pagnes, in contradiction with the well known increase of ethyl esters of most organic acids, such as ethyl lactate and diethyl succinate, during storage (RAMEYand OUGH, 1980). A possible explanation of this unexpected observation may be that a co-elution with isovaleric acid occured since it is generally accep- ted that fatty acid concentration increases during maturation of alcoholic beve- rages (NYKÄNEN, 1986; PUECHet al., 1984) and since a sweet odor was given as an odor descriptor at this LRI. Isovaleric acid eluted just before the diethyl suc- cinate (under our chromatographic conditions) and this fatty acid odor is very strong. The sweet odor was detected by all the panelists in the four extracts, hence explaining why it was not selected by the McNemar test as a factor for discriminating wine extracts. But it is nevertheless possible that the presence of
higher concentrations of this fatty acid in aged champagnes could be respon- sible for the lower diethyl succinate detection.
3-methyl-1-butanol (LRI 1323) was detected more often in the aged cham- pagnes. This observation is not surprising, because different authors such as MARAISand POOL(1980) and ETIEVANT(1991) have shown that 2-methyl-1-pro- panol and 2-phenyl-1-ethanol increase during wine aging. The increase in the release of free amino acids into the champagne bottle during aging (FEUILLAT, 1980) and the oxidative desamination of the corresponding amino acid could explain the increase of 3-methyl-1-butanol with age.
Although 3-(methylthio)-1-propanol (LRI 1733) has been reported to disap- pear during wine oxidation (FERREIRAet al., 1997), the more frequent detection of its odor in extracts of aged champagnes in this study can be explained by methionine catabolism (MULLERet al., 1971).
The odor of gamma-undecalactone (LRI 2238) was detected more often in the extract of aged samples. Other authors have shown that some lactone concentrations increased during brandy aging in wood barrels (ONISHI et al., 1977; OTSUKAet al., 1980; PUECHet al., 1984) and that these lactones are gene- rated by hydrolysis of their precursors which are extracted from the wood by the alcoholic beverage. In our case, the hydroxyacid precursor is more likely to have been formed in the champagne by oxidation of unsaturated fatty acids (TRESSLet al., 1996) remaining in the wine at the end of the fermentation. This hypothesis is supported by the fact that γ-butyrolactone was also found in increasing amounts in white wines during storage without contact with wood (FRANQUET, 1990). It is nevertheless unusual to find lactones with an odd num- ber of carbons in wine.
A sweet odor at LRI 2023 was characteristic of aged champagnes, but an explanation for this odor cannot be given because identification of the sub- stance responsible for the odor was not possible.
If we look now at the differences between the young (Ch2) and the old wine (Ch21), some differences can again be listed.
3-(methylthio)-1-propanal (LRI 1496) was more often detected in Ch21 than in Ch2 which can be explained by Strecker oxidation of methionine (WONG, 1995;
MOTTRAM, 1994) into 3-(methylthio)-1-propanal or by a simple oxidation of the corresponding alcohol, 3-(methylthio)-1-propanol, a rather abundant (800 ppb).
constituant of wine alcohols.
Ethyl furaneol (LRI 2090) was also detected more frequently in Ch21 than in Ch2. This compound was identified in Maillard reaction systems through a mechanism involving acetaldehyde, a Strecker degradation product (BLANKand FAY, 1996). These reactions were already shown to occur during wine standard aging by ESCUDERO, 1996. The “caramel” note, which was more intense in the Ch21 champagne, could be due to this compound.
Eugenol (LRI 2161) was found to be characteristic of Ch21. This observation is to be related to the data reported during white wine oxidation by FERREIRAet al. (1997), since none of the champagnes we studied were in contact with wood. The probable precursors of this phenol are lignins extracted from stems during winemaking (DZHAKHUA et al., 1978; ETIEVANT and BAYONOVE, 1983).
These precursors may then be degraded during aging on yeasts to produce dif- ferent volatile phenols and other compounds, in a process similar to aging in
wood barrels (LITCHEV, 1989; BOIDRON et al., 1988). This hypothesis is suppor- ted by the fact that some other products thought to arise from lignin degrada- tion, such as vanillin, oak lactone and acetovanillone, were described in aged wines which had no contact with wood (FERREIRAet al., 1995). The “spicy” note was slightly (but not significantly) more intense in the Ch21 champagne (figure 1). The responsible for this note could be eugenol.
Furaneol (LRI 2031) is a very unstable compound which is sensitive to oxy- gen, heat and UV radiation (GIRARDONet al., 1986; NUNOMURAet al., 1976). It is therefore not surprising that it was detected more frequently in the young cham- pagne Ch2 than in the aged samples. The “cooked fruits” note, especially
“cooked strawberry”, could be related to this compound. Its intensity was however higher in the Ch21 champagne than in Ch2, despite the lower concen- tration of furaneol in Ch21.
Two odors at LRI 1495 and LRI 2109 are also characteristic of Ch21 and Ch2 respectively.
The accelerated aging involving heating seems to generate or degrade diffe- rent compounds or odors.
2-3-butanedione was detected more often in the heated sample, than in the sample aged normally.
Benzaldehyde (LRI 1549) was found more often in the heated champagne compared to the non heated sample. The latter observation is perfectly in agre- ment with conclusions given by other authors, who claimed that benzaldehyde was formed from phenylalanine metabolism (LOYAUXet al., 1981; NYKÄNENand SOUMALAINEN, 1982). This aminoacid degradation has already been evoked twice in this paper to explain characteristics of old wines, and the conditions of storage of the wine on dead yeasts at low pH favours the increase of release of the aminoacids from proteins.
Guaiacol was characteristic of heated champagne. Perhaps the temperature increased the hydrolysis of its precursor. The “spicy” note intensity was also slightly (but not significantly) higher in the heated champagne than in the refe- rence. This note could be due to guaiacol.
Finally, the odor at 2229 is characteristic of reference champagne and disappeared with heating, although identification of the substance responsible for the odor was not possible.
If one tries to compare the two types of aging, some differences appear.
Cis-3-hexenol (LRI 1441) was an odor which is more often detected in the heated wine compared to standard aging. Heating therefore probably favours the degradation of unsaturated fatty acids remaining in the wine at the end of fermentation (VIVAS et al., 1995). Another hypothesis could be an oxidative degradation of cis-3-hexenol, generated during the pre-fermentative stages (CHI- SHOLM et al., 1995) as shown during cognac storage by SIMPSON and MILLER (1984) and NYKÄNEN (1986). It is worth noting that the “vegetal” note is more intense in the heated champagne than in Ch21. It could be due to c-3-hexenol.
The other differences are due to the detection of two odors at LRI 2158 and LRI 2221, which are more intense in the heated extract, and for which no hypo- thesis of formation or degradation can be given since identification of the sub- stances involved were not possible.
4 - CONCLUSIONS
Due to the low number of samples used in this study definite conclusions on champagne normal aging or heating cannot be drawn, and the conclusions given below should therefore be considered as indicative.
The olfactory differences detected by the frequency of detection by the panel between the accelerated and the standard agings were attributed, using GC-O, to three types of reactions favoured by the standard aging. Which are:
firstly, the Strecker reaction of amino acids into 3-(methylthio)-1-propanal and ethyl furaneol; secondly, the hydrolysis of lignin precursors to produce eugenol and thirdly the oxidation of sensitive flavor compounds such as furaneol. The heating aging is characterised by odour active substances arising from: the degradation of unsaturated fatty acids such as cis-3-hexenol; the formation of 2-3-butanedione and guaiacol from their precursors; and from phenylalanine metabolism which produces benzaldehyde.
The two aging procedures both result in compounds produced by: oxidative degradation of amino acids such as 3-methyl-2-butanol and 3-(methylthio)-1- propanol by oxidation of phenol and by oxidation of unsaturated fatty acids into hydroxyacid precursors of γ-undecalactone.
However, the overall conclusion should be that heating of champagne is not an aging method which is identical to the standard technological procedure.
ACKNOWLEDGMENTS
Thanks are expressed to C. GINIÈS for GC-MS analyses; to D. LANGLOIS for technical help and discussion and to C. VRIGNEAUfor help in sensory analyses.
This study was made possible thanks to a grant given to A. ESCUDEROby the Ministry of Education and Sciences (MEC), Spain, and to the financial support and champagne supply of Moët & Chandon (Épernay, France).
Received 30 June 1999, revised 11 January 2000, accepted 23 February 2000.
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