Premature ageing of wine aromas Denis Dubourdieu and Valérie Lavigne,

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Manifestations of defective aromatic ageing in dry white wines loss of fruity aromas appearance of heavier aromatic nuances reminiscent of wax polish or wax colour with shades of yellow associated with bitterness on the aftertaste

Olfactometric detection (C-P-G)

Comparison of aromagrams obtained from honey extracts and ones from white wine containing honey

Aromagrams of honey extracts and of white wine containing honey Sensory descriptors Retention time Organic extract Organic extract (min.) from honey from wine 10.34 strawberry 13.25 overripe pineapple 14.5 hydrocarbons 15.53 herbaceous herbaceous, forest floor 18.18 burnt meat 19.15 tobacco, cigar 19.53 cep 22.22 mushroom 22.36 vinegar grapefruit, lemon 22.55 26.37 orange 32.43 bitter almond bitter almond 32.53 candied fruit 38.17 peaches in syrup 44.02 apricot 47.44 rose rose ZO1 ZO2 50.17 honey honey 53.5 resin resin 54.22 mothballs mothballs 60.2 beeswax beeswax 62.3 vanilla vanilla

Main molecules involved in the "defective" ageing of white wines.

Aromatic markers for defective ageing of dry white wines Methional Boiled potatoes 0.5 µg/L S Methionine (Ferreira et al., 2002) Carbonyl compounds O2 O Phenylacetaldehyde Wilted roses, honey 25 µg/L Phenylalanine (Ferreira et al., 2002) N H 2 C 3 O o-aminoacetophenone Moth balls, wax polish 0.7 µg/L Indolacetic acid Oxidation

These molecules cannot alone explain aromatic defects during ageing because certain prematurely aged wines do not contain them.

Contribution of sotolon to the oxidised aroma of wine 3 * 3-hydroxy-4.5-dimethyl-2(5H)-furanone (Curry, walnuts) vins jaunes from the Jura and Sherry (Guichard et al., 1993) fig and rancio aromas of vins doux naturels (Cutzach, 1999) walnut aromas of old Port (Ferreira, 2003) aromas of defective ageing in dry white wines (Lavigne, 2002) Perception threshold of the racemic mixture 7 µg/L

Organoleptic characteristics of sotolon

Sotolon: a chiral molecule 3 O H 3 C R S The existence of one or several asymmetrical carbons can be responsible for attributing different olfactory characteristics to each enantiomer.

Perception threshold of each enantiomer of sotolon Perception thresholds (µg/L) Descriptors R 89 W alnuts , rancio S 0.8 (Curry, walnuts) Racemate 2 Model solution The S form that gives sotolon its smell and taste characteristics. . The (S)-sotolon is solely responsible for premature ageing of the aromas in dry white wines.

Distribution of various enantiomers of sotolon in dry white wines in bottle 50/50 30/70 70/30 Racemic mixutre 100 80 Excess (S)-sotolon 60 % Excess (S)-sotolon 40 20 PL 81 PL 73 EDM 00 EDM 00 Bx 99 Bx 99 PL 87 PL 75 Graves 80 Graves 81 EDM 01 The olfactory detection threshold determined from a commercial sotolon racemic mixture is insufficient to appreciate the olfactory impact of this compound on wine.

How sotolon is formed in dry white wines. aldocondensation C O O H H O O O α-ketobutyric acid Ethanal Sotolon

What are the constituents of white wines likely to prevent the formation of these compounds?

in red wines: phenolic compounds, especially anthocyanins, protect young wine from oxidative phenomena that can detract from its aroma. as for white wines, not much is known about the compounds likely to play a role. we have showed that certain sulphur peptides, in particular glutathion, can play a role

Glutathion (Glu Cys Gly) Glycine Acide glutamique Cystéine COO - H+3N CH CH2 COO - CH2 CO NH CH2 CO NH CH CH2 SH Glycine Acide glutamique Cystéine

Glutathion in must and wine

Glutathion, a natural component of grapes It has been shown to be present in large quantity in grapes: Cheynier et al, 1989; Liyanage et al., 1993 The accumulation mechanisms are not well-known. The nitrogenous intake of vines plays en essential role.

The relation between the levels of available nitrogen and glutathion in white wine must Must 1 Must 2 Must 3 Must 4 Must 5 Must 6 Must 7 Must 8 62 244 76 202 224 56 187 42 12 28 17 28 25 6 22 4 Available nitrogen (mg/L) Glutathion

Reactivity of glutathion with oxygen: formation of disulphur with quinones in the must: formation of GRP Most of the glutathion in grapes disappears when the juice is extracted.

Reaction of adding a thiol (R-SH) to the catechin quinone OH O OH Oxidation H O O H O O O O O H O H Oxidised catechin (quinone) Reduced catechin R-SH Thiol (aroma, glutathion,etc.) O H O H H O O S O H R O H adduct

Examples of glutathion content in various Sauvignon Blanc and Sémillon musts Must 1 Must 2 Must 3 Must 4 Must 5 Must 6 Must 7 Must 8 12 28 17 28 25 6 22 4 Glutathion (mg/L)

Changes in glutathion content during alcoholic fermentation

Changes in glutathion content in must during alcoholic fermentation concentration of glutathion (mg/L) 2 4 6 8 10 12 must T1 T3 T6 T9 sulphiting T20 T30

Relation between levels of glutathion in must and in young wine 9 5 4 17 2 11 7 6 22 3 Glutathion in must (mg/L) Glutathion in the corresponding wine

Relationship between the initial glutathion content of a model medium and the level at the end of alcoholic fermentation. 5 10 15 20 25 30 Concentration of glutathion (mg/L) Level of glutathion in the medium before AF Level of glutathion in the medium after AF

Relationship between the level of available nitrogen and the level of glutathion at the end of alcoholic fermentation. Concentration of glutathion (mg/L) 25 20 15 T0 10 End of AF 5 48 96 190 Level of available nitrogen in the model medium (mg/L)

Signs of premature ageing of aromas in white wines

During ageing

Traditional ageing on the lees Protection of the young wine's fruity aromas Maintaining wine in a state of oxidation-reduction to encourage the appearance of a bouquet showing signs of reduction: truffle, burnt and mineral nuances . Avoids or delays manifestations of aromatic ageing

Influence of ageing techniques on the defective ageing of wine Ageing with or without the lees New or used barrels Evolution - of the fruity aroma - of defective ageing markers - of glutathion

Concentration of 3-M (ng/L) Changes in the level of 3-MH in a Sauvignon Blanc wine aged different ways in barrel Concentration of 3-M (ng/L) 200 400 600 800 1000 1200 1400 1600 End of AF November April Used Barrel Used barrel Used barrel New barrel racked racked

Amount of sotolon in the wines at the end of barrel ageing Concentration of sotolon (µg/L) 1 2 3 4 5 6 7 8 9 Detection threshold (white wine) Barrel Used barrel Barrel New barrel used on the lees without lees new on the lees without lees

Effect of barrel ageing techniques on changes in the glutathion level of wines concentration of glutathion (mg/L) 2 4 6 8 10 12 14 16 18 new barrel on the lees new barrel without lees used barrel on the lees used barrel without the lees Samples End of AF December January February May

Glutathion, sotolon and 3-mercapto-hexanol at the end of barrel ageing Glutathion, a natural component of grapes makes it possible to prevent the defective ageing of white wines. Used barrel on the lees New barrel without the lees Glutathion Sotolon 3-MH 5.8 0.5 1.3 9.7 1400 420 (mg/L) (µg/L) (ng/L) The same ageing conditions most conducive to preserving the aromatic characteristics of dry white wines also limit a decrease in the level of glutathion.

Interpretation of the protective role of lees with regard to defective aromatic ageing Release of reductive compounds Oxygen fixation by the lees

Oxygen consumption (µg/L/h) of a white wine aged for 6 months entirely its lees Wine aged on its lees 611 Filtered wine 0.01 Lees alone 542 Heat-treated lees 19 (Fornairon et al., 1999)

Manifestation of premature ageing once the wine is bottled

Identification of the random nature of premature ageing in two dry white wines (tasting in 2005 of 12 bottles of each wine) 70 60 Graves 2001 50 % 40 30 20 10 Little or no signs of age Showing average signs of age Looking very aged 70 1997 Pessac Léognan 60 50 40 % 30 20 10 Little or no signs of age Showing average signs of age Looking very aged

Importance of oxidative-type reactions throughout bottle ageing Correlation between the oxygen dissolved in bottled wines and prematurely-aged aromas Analyses of 20 samples of a Graves white wine (1997 vintage) after 7 years in bottle. Average 6.00 R 2 0.7084 5.00 4.00 3.00 2.00 1.00 0.00 20 40 60 80 100 120 140 Dissolved oxygen (µg/l) Importance of oxidative-type reactions throughout bottle ageing

Effect of dissolved oxygen content on colour 2 R = 0.8315 0.4 0.3 DO420 nm 0.2 0.1 10 20 30 40 50 60 70 80 90 Level of dissolved oxygen (µg/l)

Correlation between free SO2 and dissolved oxygen 25 20 15 Free SO2 (mg/l) 2 R = 0.7909 10 5 20 40 60 80 100 120 140 Level of dissolved O2 (µg/l)

Choice of closure… R 2 = 0.7191 Dissolved oxygen in bottle (µg/l) 0.5 1 1.5 2.5 3 3.5 20 40 60 80 100 120 140 Dissolved oxygen in bottle (µg/l) Concentration of sotolon (µg/L)

Dissolved oxygen measured in white wine six months after bottling Effect of closure… 120 100 80 Level of oxygen (µg/l) 60 40 20 1 2 4 5 3 Types of closure used

Changes in the level of free SO2 in bottle Effect of closure… 30 25 Free SO2 (mg/l) 20 15 1 2 3 4 5 Types of closure used

To prevent the defective ageing of white wines, IT IS NECESSARY TO have vines with sufficient vigour limit the extraction of phenolic compounds during pressing protect both the must and the wine from oxidation make sure that alcoholic fermentation is completely finished reduce the lag period for malolactic fermentation age the wines in reductive conditions limit the dissolution of oxygen when preparing the wine for bottling choose a closure that is suited to the wine