Natural Malo-Lactic Fermentation in New York State Wines

Malo-lactic fermentation was studied in production lots of nine wines from Vitus labrusca and hybrid varities of grapes. Fixed acids, lactic acid, and glycerol were determined by gas chromatography. The development of lactic acid organisms was followed by conventional plate counts with a tomato juice-wine agar medium. Malic acid was converted to lactic acid when the bacterial population reached or exceeded 106cells/ml and the culture was passing from the exponential growth phase to the stationary phase. No increase of lactic or acetic acid was noted during the 2-6-week period of growth, preceding malic to lactic conversion. When the conversion was complete, a stoichiometric relation was found between malic acid lost and lactic acid produced. Volatile acidity, as acetic acid, increased following the malic to lactic conversion. Tartaric acid decreased in two stages, initially from decrease in temperature, and later apparently from an increase in pH following the malic to lactic conversion. No changes were observed in succinic acid, glycerol, or total reducing sugars.