Winemaking: Yeast Nutrition Vital for Wine Fermentation

(Wines&Vines) - They are some of the questions that can keep a winemaker up at night during harvest.

• Is that tank starting to smell a bit funky?

• That lot was at 10º Brix yesterday and it was still there this afternoon, are things stalling?

• We inoculated those barrels days ago, what’s the hold up?

 The questions stem from nagging concerns about fermentation brought on by the stress of harvest and the inherent uncertainties of putting one’s trust in microbes. In a session appropriate for the pre-harvest season, a panel of University of California, Davis, professors and yeast experts offered insights into wine fermentation research, yeast biology and best practices to ensure an efficient and healthy fermentation during a daylong session earlier this month.

Dr. Linda Bisson, a yeast expert with UC Davis, organized the seminar and provided an overview of problematic fermentations. The causes of stuck or sluggish fermentations are 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.

 Common causes

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. 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. 

She also touched on some of her new research regarding juices that regularly exhibit difficult fermentations. “By difficult I mean you’re doing everything right and the yeast are still struggling with these juices,” she said.