Melanie Nicholls, Michael Qian, and James Osborne*
*Oregon State University, Wiegand Hall 108A, 3051 SW Campus Way, Corvallis, OR 97331 (james.osborne@oregonstate.edu)

This study investigated whether adding a non-Saccharomyces yeast culture during prefermentation cold soaking could act as a bio-protectant against Hanseniaspora uvarum. Initial experiments tested the ability of three non-Saccharomyces yeast cultures to suppress H. uvarum and acetic acid production during a simulated cold soak in a model grape juice. Two different initial populations of H. uvarum were inoculated to mimic healthy grapes (low H. uvarum population) or damaged grapes (high H. uvarum population). All three non-Saccharomyces yeasts repressed the growth of H. uvarum to varying degrees. Metschnikowia fructicola and Torulaspora delbrueckii were more effective than Lachancea thermotolerans and growth repression was greater if the initial population of H. uvarum was low. The addition of non-Saccharomyces cultures also decreased production of acetic acid by H. uvarum by up to 50%. Additional experiments tested the efficacy of the non-Saccharomyces cultures at different temperatures, with or without added SO2. M. fructicola was still effective at repressing H. uvarum growth and acetic acid production after an addition of 20 mg/L SO2, but T. delbrueckii was only effective if no SO2 was added. At 40 mg/L SO2, H. uvarum populations declined whether M. fructicola or T. delbrueckii had been added or not. However, H. uvarum populations recovered near the end of the cold soak when grown alone, while populations remained low if M. fructicola or T. delbrueckii was added. The greatest reduction in acetic acid occurred when M. fructicola and 20 mg/L SO2 were added. In these treatments, a 58% reduction in acetic acid was measured. Additional experiments are currently being conducted using Pinot noir grapes.

Funding Support: Northwest Center for Small Fruits Research