Production of Fatty Acids during Alcoholic Wine Fermentation under Selected Temperature and Aeration Conditions

The synthesis of medium chain saturated fatty acids (MCFA, toxic to yeast cells) and long chain unsaturated fatty acids (LCUFA, required for yeast survival) during alcoholic wine fermentation was examined. The contents of MCFA and LCUFA during laboratory scale alcoholic fermentation of Carménère using Saccharomyces cerevisiae yeast were tracked in 19 fermentations under selected temperature and aeration conditions. Fermentations were sampled daily and analyzed for fatty acids using a gas chromatograph with flame detector. Fatty acid synthesis was greatest under normal fermentation conditions (28°C, pH 3.5, aeration at the beginning of fermentation), and both MCFA and LCUFA were reduced at 24 and 32°C. Although fatty acid concentrations increased at the same fermentation stage, they never exceeded the production levels observed under normal fermentation. The MCFA/LCUFA ratio at 32°C was between 3.55 and 4.43, due to significantly increased MCFA production at this temperature; we recommend keeping fermentations below 28°C. Under anaerobic conditions, the MCFA/LCUFA ratio was very high compared to the other aeration strategies, showing that oxygen improves fermentation performance by limiting MCFA synthesis, which can cause stuck and sluggish fermentations. Aeration at the beginning and at the end of the exponential phase maintained the MCFA/LCUFA ratio below 1.0, indicating a greater production of LCUFA when oxygen is used during the fermentation.