is sulfites, sulfur compounds that can induce an allergic reaction in sensitive people The second additive is either sugar or acid, and it is used to correct the balance between these two substances Grapes that ripen in a cool climate can lack the sugar to produce enough alcohol for a stable wine; grapes that ripen in a hot climate metabolize some of their acids and can produce a flat-tasting wine French winemakers usually add sugar; California winemakers often add tartaric acid The Alcoholic Fermentation The Fermentation Yeasts Fermentation can begin with or without the addition of a starter culture of yeast The winemaker can choose among many different strains of Saccharomyces, or allow the fermentation to begin spontaneously with “wild” yeasts from the grape skins (species of Kloeckera, Candida, Pichia, Hansenula, and others) These are always eventually displaced by Saccharomyces cerevisiae, which has a greater tolerance for alcohol, but they contribute flavor compounds to the finished wine The primary job of the yeast is to convert sugar to alcohol, but it also produces various volatile, aromatic molecules that the grape itself cannot supply Prominent among them are the longer-chain alcohols, and esters, a class of compounds that combine an acid with an alcohol or phenol Both yeast and grape enzymes and the acid conditions also liberate aromatic molecules from the nonvolatile sugar complexes in which some are stored in the grape, so fermentation also brings out the grape’s own flavor potential Temperatures and Times The winemaker varies the conditions of fermentation according to the particular kind of wine being made In the case of delicate white wines, the must is fermented for four to six weeks at ... Prominent among them are the longer-chain alcohols, and esters, a class of compounds that combine an acid with an alcohol or phenol Both yeast and grape enzymes and the acid conditions also liberate... aromatic molecules from the nonvolatile sugar complexes in which some are stored in the grape, so fermentation also brings out the grape’s own flavor potential Temperatures and Times The winemaker varies the conditions... alcohol, but they contribute flavor compounds to the finished wine The primary job of the yeast is to convert sugar to alcohol, but it also produces various volatile, aromatic molecules that the grape