Volatile Compound Formation in White Wines Fermented Using Immobilized and Free Yeast

Abstract

Using free yeast or yeast immobilized in double-layer Ca-alginate gel beads or strands, or single-layer beads or strands, white table wines were made from Koshu grape musts with initial pH between 2.80 and 3.70, containing 0 to 325 mg SO₂/L and 477 to 2178 mg total phenols gallic acid equivalent (GAE)/L, at fermentation temperatures ranging from 10 to 40°C. Yeast cells immobilized in beads could be added to and removed from fermenting vessels more easily than those in strands and markedly more easily than free yeast cells. Yeast immobilized in double-layer beads produced the most visibly clear wine, with the least leakage of viable cells from the gel matrices into the wine at the end of the fermentation process. Double-layer bead-immobilized yeast was also more tolerant than free yeast of high SO₂ and phenol concentrations, low pH, and high fermentation temperature. Fermentations with both immobilized and free yeast were negligibly influenced by differences in the initial pH. Lower concentrations of undesirable volatile compounds, such as methyl alcohol, ethyl acetate, and acetaldehyde, were observed in wines made using yeast immobilized in double-layer beads than in wines produced with free yeast. Concentrations of major higher alcohols (aroma compounds) varied with the use of either immobilized or free yeast, the SO₂ concentration in the must, and the fermentation temperature.