Freeze-desiccation survival in wild yeasts in the bloom of icewine grapes

To determine the response of different wild yeasts and yeast-like molds of importance to icewine producers, to freezing and desiccation at -25 degrees C, a modified AOAC hard surface carrier test was performed on the 12 most commonly found wild yeast species on grapes grown in the Niagara Peninsula. The initial concentration was similar to 10(5) cfu ml(-1) and after 20 days exposure, six species had no log reduction, three had a one log reduction and three had a 2-log reduction. After 40 days, only two species (Candida stellata and Cryptococcus laurentii) exhibited a 5-log reduction (i.e. no survivors). Candida steatolytica, Metchnikovia pulcherrima, Pichia kluyveri and Saccharomycopsis crataegensis were particularly resistant with log reductions of 2, 2, 3, 4, respectively, after 104 days. Given a frequency of similar to 1.0 days per winter at -25 degrees C in the Niagara grape growing region, it is unlikely that freeze-desiccation alone is responsible for fluctuations in species frequency of wild yeasts of icewine grapes. There was no correlation between the species frequency at the fall harvest time and ability to survive freeze-desiccation. (C) 1998 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd. All rights reserved.