James Osborne,* Michael Qian, and Melanie Nichols
*Oregon State University, 100 Wiegand Hall, Oregon State University, Corvallis, OR, 97331 (james.osborne@oregonstate.edu)

Growth of Hanseniaspora uvarum during prefermentation maceration (cold soaking) can result in excessive production of ethyl acetate, resulting in wines with a notice­able nail polish remover aroma. Typically, an addition of SO2 is made at the start of cold soaking to inhibit H. uvarum growth. However, renewed emphasis on lowering the amount of SO2 used during winemaking has led to exploration of alternative methods, such as the use of non-Saccharomyces yeast as bio-protectants to prevent microbial spoilage. This study investigated the effectiveness of non-Saccharomy­ces yeast in combination with SO2 to reduce H. uvarum growth and ethyl acetate production during prefermentation cold soaking. Six-day cold soaks of Pinot noir grapes were conducted at 10°C with the addition of 0, 25, 50, or 75 mg/L SO2 and/ or Metschnikowia fructicola or Torulaspora delbrueckii at ~105 CFU/mL. The addition of 0 or 25 mg/L SO2 had little impact on H. uvarum growth whether M. fructicola or T. delbrueckii had been added or not. Reduced growth of H. uvarum was observed when 50 mg/L SO2 was added, but lower H. uvarum populations were observed if M. fructicola was also added. Increasing the amount of SO2 added significantly reduced production of ethyl acetate, as did the addition of M. fructicola. The addition of M. fructicola alone was as effective at reducing ethyl acetate as an addition of 50 mg/L SO2. Significant interactions between SO2 concentration and addition of M. fructicola were also noted. In contrast to M. fructicola, the addition of T. delbrueckii did signifi­cantly impact the production of ethyl acetate. These results suggest that M. fructicola could be used to lower the amount of SO2 needed to be added during cold soaking to prevent spoilage by H. uvarum.

Funding Support: Northwest Center for Small Fruits Research