Issue link: http://winesandvines.uberflip.com/i/172581
OCTOBER NEWS Dr. Linda Bisson encouraged growers whose vineyards are prone to stuck fermentations to send juice samples to the University of California, Davis. Yeast Nutrition Vital For Wine Fermentation Enology experts discuss research and best practices at UC Davis D avis, Calif.—In a session appropriate for the pre-harvest season, a panel of University of California, Davis, professors and yeast experts offered insights into the best practices to ensure an efficient and healthy fermentation during a daylong seminar in August. Dr. Linda Bisson, a yeast expert with UC Davis, organized the seminar and provided an overview of problematic fermentations. Bisson said stuck or sluggish fermentations are often caused by insufficient or imbalanced nutrients, ethanol toxicity, the presence of toxic substances, a yeast strain that's ill suited for the particular must or juice, low pH and temperature shock. Toxic substances include acetic acids produced by stressed yeast or other microbes. The acids may have occurred in the vineyard but don't cause problems until the fermentation has produced a certain level of ethanol, Bisson said. Sluggish or slow fermentations indicate there's something out of balance with the fermentation, while a complete stop is likely the result of a misguided step such as making a pH adjustment in the middle of fermentation. "Usually, if there is an abrupt stop, it's because someone did something to cause it," Bisson said. Dr. Nichola Hall, a technical representative with Scott Laboratories, said the yeast assimilable nitrogen, YAN, requirements for one strain of yeast to consume 1 gram of sugar could be twice that of different yeast. Hall said yeasts also require several nutrients working in tandem so that they can process wine sugars effectively. The host of other microbes usually present in cold soak can rapidly deplete the amount of nutrients, and Hall suggested winemakers should run a complete nutrition check after cold soak, going so far as to say a YAN analysis prior to winesandvines.com cold soak "is almost a waste of analysis." Learn more: Search keywords Darren Michaels, technical representative "Fermentation seminar." for Laffort USA, said specialty strains offer nuances in mouthfeel, aroma, color and other more specialized considerations such as less foam production (good for barrel-fermented Chardonnay), VA production and the ability to mask green flavors. But yeast can only impart those characteristics if it has the nutrients it needs and is within its pH, temperature and alcohol comfort zones. "If you can't control fermentation temperature, it would be hard to say that strain is going to give you what you want," he said. —Andrew Adams 16 W in e s & V i ne s O C TOB E R 20 13