PROGRESS OF STUDIES OF LEES ORIGINATING FROM THE FIRST ALCOHOLIC FERMENTATION OF CHAMPAGNE WINES

Malolactic fermentation (MLF)¹, the decarboxylation of L-malic acid into L-lactic acid, is performed by lactic acid bacteria (LAB). MLF has a deacidifying effect that may compromise freshness or microbiological stability in wines² and can be inhibited by fumaric acid [E297] (FA). In wine, can be added at a maximum allowable dose of 0.6 g/L³. Its inhibition with FA is being studied as an alternative strategy to minimize added doses of SO₂⁴. In addition, wine yeasts are capable of metabolizing and storing small amounts of FA and during alcoholic fermentation (AF).

Sforzato di Valtellina DOCG is a special dry red wine produced from partially dehydrated Nebbiolo wine-grapes growing in the Rhaetian Alps valley of Valtellina (Lombardy, Italy). Valtellina terraced vineyards are located at an altitude of 350–800 m according to ‘heroic’ viticulture on steep slopes. The harvested grape bunches are naturally dehydrated indoors, where a slow and continuous withering occurs (about 20% w/w of weight loss), until at least 1st December when the grapes reach the desired sugar content and can be processed following a normal winemaking with maceration.

Malic acid has a strong impact on wine pH and the contribution of fermenting yeasts to modulate its concentration has been intensively investigated in the past. Recent advances in yeast genetics have shed light on the unexpected property of some strains to produce large amounts of malic acid (“acidic strains”) while most of the wine starters consume it during the alcoholic fermentation. Being a key metabolite of the central carbohydrate metabolism, malic acid participates to TCA and glyoxylate cycles as well as neoglucogenesis. Although present at important concentrations in grape juice, the metabolic fate of malic acid has been poorly investigated.

Enzymatic browning (BE) of must is caused by polyphenol oxidases (PPOs), tyrosinase and laccase. Both PPOs can oxidize diphenols such as hydroxycinnamic acids (HA) to quinones, which can later polymerize to form melanins [1], which are responsible of BE in white wines and of oxidasic haze in red wines. SO₂ is the main tool used to protect must from BE thanks to its capacity to inhibit PPOs [2]. However, the current trend in winemaking is to reduce and even eliminate this unfriendly additive. Among the different possible alternatives for protecting must against BE, the inoculation with a selected Metschnikowia pulcherrima MP1 is without any doubt one of the most promising ones.

Mycobiota encountered from vine to wine is a complex and diversified ecosystem that may impact grape quality at harvest and the sensorial properties of wines, thus leading to off-flavors [1-3]. Among known off-flavors in wine, fresh mushroom aroma (FMA) has been linked to some mold species, naturally pre-sent on grapes, producing specific volatile organic compounds (VOC) [4-5]. The most well-known are 1-octen-3-ol and 1-octen-3-one, although many other VOC are likely involved. To better understand the FMA defect, biotic and abiotic factors impacting growth kinetics and VOC production of selected fungal species in must media and on grapes were studied.