YEAST SELECTION TRIALS FOR COLD-HARDY GRAPES

By Katie Cook, Enology Project Leader of University of Minnesota, Horticulture Research Center

One of the questions winemakers in northern climates ask most often is what yeast strains are recommended for fermenting various cold-hardy grape cultivars. While I understand why this question is asked – most catalogs selling yeast don’t list ‘Marquette’ or ‘Frontenac’ as recommended cultivars for a particular strain – it is also difficult to give a recommendation based on grape cultivar alone. Variables such as growing conditions of the grapes, winemaking conditions in the cellar, and stylistic goals are all important factors in determining what yeast should be used for making a certain wine. Vintage variation (especially in northern climates) can mean that a certain outcome with a commercial yeast strain one year doesn’t necessarily mean that we will have the same outcome the following year. Yeast can’t enhance the spicy character of Marquette, for example, if the aroma compound(s) responsible for that character aren’t in the grapes when they are harvested. Complicating matters is the fact that we are just beginning to learn what aromatic compounds might be involved in varietal aroma for these grapes!

Development of new yeasts

Before a new commercial yeast strain is released, it undergoes extensive fermentation trials, from lab-scale to commercial scale and with various grape cultivars, to understand its impact on the wine. These trials require a great deal of costly research in order to be certain that the yeast activity will be fully understood once it is released. Unfortunately, the costs of this research guarantees that more obscure grape cultivars are not typically used in these trials. You are about as likely to see yeast recommendations for Picpoul or Vermentino as you are Marquette or Frontenac Gris. Fortunately, with the assistance of the Northern Grapes Project, researchers in the Midwest and Eastern US will be able to perform small-scale yeast trials this year for our cold-hardy grape cultivars.

Yeast trials

While we may already have some ideas of how certain yeasts behave with cold-hardy varieties, we have yet to perform a study that includes statistical analysis of sensory data in replicated wine trials. This will allow us to evaluate whether a certain aroma or flavor can be attributed to a difference in yeast, grape cultivar or to the growing conditions. Although we do not fully understand the key aromatic compounds involved in the varietal aroma of cold hardy wines, we are able to build on knowledge gained from studies of of wine aroma and yeast metabolism to make educated yeast and cultivar matches. After several years of trials, we will be able to give confident recommendations for yeast strains to winemakers desiring a certain style wine from their cold-hardy grapes …

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