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w i n e M A K IN G 6 H2S (mg/L) 5 4 OH 3 R 2 Flavan-3-ol 1 0 OH No Cu added (total Cu 0.2 mg/L) Cu added (total Cu 0.5 mg/L) Figure 2: Distribution of H2S concentration after six months of bottle storage for Sauvignon Blanc wines added or not with copper before bottling. The two groups were significantly different at 95%. "Empyreumatic" is another term sometimes used to describe complex wine attributes as smoky, roasted meat or toasty bread crust, which can be present in barrel-fermented wines, but also, for wines that have not been in contact with oak, after a certain period of bottle ageing. Such empyreumatic aromas have been associated with volatile thiols such as 2-methyl-3-furanthiol and furfuryl thiol,7 the latter a key compound in coffee aroma. Oxygen Reaction with varietal thiols O O R Quinone Loss of fruity aromas Reaction with smoky/mineral thiols Modulation of empyreumatic/ mineral aromas Reaction with reductive thiols Modulation of reductive off-odors Figure 3: Oxygen influence on wine volatile thiols and consequent sensory implications. Volatile thiols and reduction In spite of the potentially favorable outcomes of having certain volatile thiols in wine, there is another side of volatile thiols that is not associated with development of pleasant or complex characters. "Reduction" is a term often used in wine tasting to designate wines having unpleasant odors of cabbage and rotten egg, which have been associated with the presence of certain thiols such H2S and methyl mercaptan (MeSH). The origin of these thiols in wine is complex, and their occurrence and concentration depend on multiple factors. Yeast fermentation is frequently associated with the occurrence of a rotten egg off-odor due to production of H2S by the yeast. While this reduction can be quite intense, most wines at the end of fermentation exhibit low levels of perceived reduction, and typically low H2S levels. Anecdotal evidence indicates that, during further processing and storage of wines in the cellar—for example, during tank or barrel maturation with or without lees—reductive characters might reoccur and require specific intervention to be eliminated. Generally speaking, under the condition commonly adopted in the modern wine industry, most wines are manny@boutes.com pr actica l win ery & vin eya r d JANUARY 20 14 5