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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

Using specialized yeast to reduce the alcohol content of wine

Due to wine-making trends and the effects of climate change, the alcohol content of wine has been creeping up over the last twenty years. This upward drift has sparked concern among those in the industry because alcohol content not only affects the sensory properties of wine but also the health of consumers. These worries have prompted INRA researchers to experiment with strains of a yeast (Saccharomyces cerevisiae) currently used in commercial wine production; these strains produce less alcohol during fermentation. Scientists have managed to reduce a wine’s alcohol content by 1.3%.

Updated on 12/22/2016
Published on 06/16/2014

In most wine-producing countries, wine-making trends, notably the tendency to harvest riper grapes to produce wines with higher quality sensory attributes, have resulted in the production of higher alcohol wines; alcohol content has climbed by about 2% over the last 20 years. This increase has been exacerbated by climate change and is worrisome for several reasons. First of all, at high levels, ethanol can change the sensory properties of wine because it interacts with certain aromatic compounds. Second, because of consumer health concerns and preventative health policies, the market is shifting towards wines with more moderate levels of alcohol. Third, in some countries, economic constraints come into play because wines are taxed based on alcohol content.

INRA researchers in Montpellier have managed to apply artificial selection to a Saccharomyces cerevisiae strain that is already widely used in the commercial production of wine. They have obtained yeast strains that yield lower levels of alcohol, a promising result given this dilemma. The research world has already spent over a decade trying to develop such strains. To arrive at this goal, researchers needed to produce yeast that would ferment sugars in such a way as to yield less ethanol and higher levels of alternative byproducts, such as glycerol.  The method currently employed by researchers involves culturing yeast in a medium with controlled levels of salinity, which selects for and thus favors the spread of natural mutations that result in a greater production of glycerol.

Using this approach, INRA researchers have managed to obtain strains that demonstrate modified fermentation: they produce more glycerol (the compound that adds to a wine’s body and sweetness) and 2,3-butanediol (which has no effect on taste) without generating high levels of undesirable metabolites. The researchers conducted a pilot study in which they added one of these strains to grape must, and the wine produced contained 1.3% less alcohol than normal.

This method could therefore serve as an effective means of reducing the alcohol content of wine without having to employ genetically modified organisms. However, more research is needed before these yeast strains can be commercialized; specifically, researchers need to find a way to produce yeast under conditions that meet wine-making requirements.

This research came out of a thesis funded by a CIFRE contract between INRA and the Lallemand company, which produces yeast specialized for wine-making applications. It has led to a patent application: “Method for obtaining low ethanol-producing yeast strains, yeast strains obtained therefrom and their use” (dated January 21, 2014; reference number 5572550-2EP).

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Valentin Tilloy, Anne Ortiz-Julien and Sylvie Dequin. Reducing ethanol and improving glycerol yield by adaptive evolution of Saccharomyces cerevisiae wine yeast under hyperosmotic conditionsAppl. Environ. Microbiol., 14 February 2014.  DOI: 10.1128/AEM.03710-13