The evolution of low molecular weight alcohols during wine fermentation: Effects of yeast strain ester productivity and nitrogen supplementation

Volatile, low molecular weight alcohols ranging in size from three to eight carbon atoms are produced during yeast fermentation. Straight-chain, branched-chain and cyclic molecules are included in this designation. Methanol is also a low molecular weight alcohol, but it is present in grape must and not affected by fermentation. Low molecular weight alcohols affect the perception of wine quality and are precursors to esters, a class of generally desirable aroma compounds. Ester productivity is an inherent characteristic of yeast, but it has not been made clear whether there is a correlation between ester production and low molecular weight alcohol production for a given yeast strain. Nitrogen supplementation is also an important factor in the development of both compounds: it has been shown that high levels of nitrogen in must produce wines high in esters but low in volatile alcohols. The source of nitrogen should also have an effect, since amino acids are direct precursors to some low molecular weight alcohols.;The present study used a gas chromatographic method coupled with headspace solid phase microextraction (HS-SPME-GC) to evaluate the production of low molecular weight alcohols by three yeast strains of varying ester productivity. A nitrogen poor Chardonnay must was used, and additions of diammonium phosphate or amino acid mixtures were tested. The concentration of nitrogen in those fermentations to which additions were made was 200 mg/L. Methanol, 1-propanol, ethyl acetate, 2-methyl-1-propanol, 1-butanol, 3- and 2-methyl-1-butanol, 1-hexanol and phenylethanol were monitored. Nitrogen utilization was also monitored.;The yeast strain had an effect on 2-methyl-1-butanol, 1-propanol and ethyl acetate concentrations. The high ester producing yeast evolved higher levels of 1-propanol and ethyl acetate, but not 2-methyl-1-butanol. Nitrogen supplementation had an effect on 2-methyl-1-butanol and phenylethanol concentrations. Utilization of amino acid precursors increased upon the addition of either form of nitrogen.;This research indicates that when must nitrogen concentration is low, adding moderate amounts of nitrogen prior to fermentation does not significantly affect the production of low molecular weight alcohols. Furthermore, yeast strain ester productivity does not appear to have an effect on the ability of a yeast strain to produce low molecular weight alcohols.