Wine cellar in the Agronomy and Viticulture Experimentation Unit at the INRA center in Colmar. Opening of a cask used in a microvinification experiment. © INRA, MAITRE Christophe

Yeast: how wines get made

By Pascale Mollier, translated by Jessica Pearce
Updated on 12/23/2016
Published on 09/28/2016

If you enjoy wine, you have yeast to thank. This report summarizes the results of recent INRA research examining the origin, diversity, evolution, and artificial selection of yeasts, the microorganisms that make alcoholic fermentation possible.

You cannot make wine without yeast. Yeast strains carry out alcoholic fermentation in the grape must, transforming sugars into ethanol.

Some winemakers use yeasts that naturally occur on grapes and in wine cellars. However, where do these yeasts come from originally? Recent research has shown that they live on grapevines and are transported by insects such as fruit flies, bees, and wasps; they hitch a ride in the insects’ digestive tracts. Yeasts are also maintained over time thanks to these insects, and especially wasps, which pass strains to their larvae via regurgitated food and inoculate new grape berries when biting into them (see article 1: Wine-making wasps).

However, around 80% of winemakers add commercial yeasts to their grape must. More than 200 strains of active dry yeast are available on the market.

For the most part, commercial yeasts are the result of artificial selection applied to Saccharomyces cerevisiae strains isolated from wine. In 2009, thanks to a collaboration between INRA researchers and the French National Genotyping Institute (CNG), the first complete genome for a wine yeast strain was obtained.

INRA researchers have also been studying yeast evolution. Recent studies have shown that yeasts exchange genes that provide a selective advantage in the grape-must environment. These genes code for peptide transporters, which enhance the use of nitrogen-based resources and increase growth levels and fermentation efficiency. The presence of these genes could therefore be used to breed better wine yeast strains or improve existing ones (see article 2: The genes specific to wine yeasts).

INRA researchers have also tackled the question of where Saccharomyces cerevisiae wine yeasts come from. In collaboration with scientists at the University of Lisbon, they have shown that wine yeasts are closely related to yeasts isolated from oak trees in the Mediterranean (see article 3: Wine yeasts descended from Mediterranean oak yeasts).

Wine yeasts have been shaped by artificial selection for thousands of years. Having a complete genome for S. cerevisiae has made it possible to focus on different targets for further selection, such as the following:

  • Production of yeasts that yield more acidic, less alcoholic wine; such yeast strains became commercially available in 2016 (see article 4: Using specialized yeast to reduce the alcohol content of wine).
     
  • Production of a yeast strain that generates large quantities of aromatic compounds (especially esters). Such a strain was commercialized in 2012 and was used in a study seeking to optimize aroma production during fermentation by adjusting nitrogen concentration and temperature (see article 5: Optimizing aroma formation during fermentation).
     
  • Production of yeasts that yield low levels of sulfur dioxide.