Grapes grown in New York and many other states often have low yeast available nitrogen in musts. Insufficient yeast available nitrogen is a major cause of stuck or sluggish fermentation in wine production, and is also related to a wine disorder called “atypical aging”. The objective of this study was to optimize soil and foliar nitrogen application to improve yeast available nitrogen in grape must. We set up a field trial in a Riesling vineyard in the Finger Lakes Region to test the combination of three levels of soil nitrogen application and three levels of foliar nitrogen application on vine nitrogen status, berry yield, and juice yeast available nitrogen level for two years. We found that the effect of foliar nitrogen application on juice yeast available nitrogen depends on weather patterns and vine background nitrogen status. There is a greater need for foliar N application in a dry year and the effect of foliar nitrogen application on juice yeast available nitrogen is larger in a dry year. This has provided grape growers a management tool to improve yeast available nitrogen in grape musts. The findings of this study and our previous work on the topic have been disseminated to grape growers in New York and the Northeast in a timely manner. As a result, many growers are now using foliar nitrogen application around veraison to increase juice yeast available nitrogen level, especially in dry years.

Grapes grown in the state of New York and many other states often have low yeast available nitrogen (ammonium and amino nitrogen) in musts. Surveys conducted in New York showed that yeast available nitrogen levels of musts from most vineyards are well below the threshold (330 to 400 mg/l) suggested by studies in Australia and California. Insufficient yeast available nitrogen in grape must is the major cause of stuck or sluggish fermentation in wine production, which contributes to formation of off-flavors in wine. One of the wine disorders associated with low yeast available nitrogen is called “atypical aging”, which causes significant losses to the wine industry. It is estimated that as much as 20% of the white wines produced in New York can be affected by this wine disorder. Although supplemental nitrogen such as diammonium phosphate can be added to grape must to promote complete fermentation, research in Germany indicated that this practice does not reduce the occurrence and development of atypical aging. Our previous work showed that wine atypical aging is triggered by water stress and nitrogen deficiency in the vineyard. Therefore optimizing vine nitrogen status and yeast available nitrogen level in grape musts via water and nitrogen management in the vineyard appears to be the most effective way of reducing the occurrence of atypical aging.

The objective of this study was to optimize soil and foliar nitrogen applications to improve juice yeast available nitrogen level and fruit quality, thereby reducing the occurrence or intensity of atypical aging in white wines. We set up a file trial in a Riesling vineyard in the Finger Lakes Region to test the combination of three levels soil nitrogen application (two weeks before and one week after bloom) and three levels of foliar nitrogen application (around veraison) on vine nitrogen status, berry yield and juice yeast available nitrogen level for two years. We found that the effect of foliar nitrogen application on juice yeast available nitrogen depends on weather patterns and vine background nitrogen status. Foliar N applications around veraison significantly increased juice yeast available nitrogen during the 2004 wet season, and three times of foliar spray appeared to be as effective as five times of foliar spray treatment. In the 2005 season, which was dry and warm, soil N application early in the season improved vine N status and slightly increased juice yeast available nitrogen; foliar nitrogen sprays were more effective in increasing juice yeast available nitrogen compared with 2004. Soil N application or foliar nitrogen sprays did not significantly affect fruit yield in either year. These results indicate that there is a greater need for foliar N application in a dry year and the effect of foliar N spray on juice yeast available nitrogen is larger in a dry year.

The findings of this study and our previous work on the topic have been presented to the New York grape/wine industry at the NY Wine Industry Workshop, the Finger Lakes Grape Growers Convention, Grapevine Nutrition Workshops, Geneva Fruit Field Day, and Great Lakes Fruit Workers In-Service Training Meetings. As a result, more vineyards are now installing irrigation systems to maintain good vine water status and improve juice yeast available nitrogen levels. In dry years, many growers are using foliar nitrogen applications around veraison to increase yeast available nitrogen in musts following our recommendation to reduce the risk of wine atypical aging.

grape and wine quality