Wine yeast. The invisible winemaker.

What yeast does

During fermentation, yeast eats the sugar in grape juice and turns it into alcohol and carbon dioxide. The main wine yeast is Saccharomyces cerevisiae, the same species used for bread and beer.

Yeast also produces aromatic compounds and releases aromas that are hidden in the grape. Two batches of the same juice fermented with different yeasts can smell and taste noticeably different.

Native or wild yeast

Grapes and cellars naturally carry many yeasts. A “native”, “wild” or “indigenous” fermentation relies on these yeasts instead of adding a commercial culture. Several species start the fermentation, then the stronger Saccharomyces takes over as alcohol rises.

Many winemakers believe this gives more complexity and a stronger sense of place. The risk is that fermentations can be slow, can stop before all the sugar is gone, or can produce off-flavors.

Commercial yeast

Selected yeast strains are bought as dried cultures. They start quickly, finish reliably and are chosen for specific results, for example to bring out the aromas of Sauvignon Blanc or to cope with high sugar levels.

Critics say they can make wines more uniform. Supporters point out that reliability matters, especially in difficult vintages, and that the grapes still speak.

The best of both: selected native yeasts

A newer approach is to isolate the best indigenous yeasts from a specific vineyard, test them in the lab and multiply them. The winemaker then gets the reliability of a selected culture with yeasts that truly belong to the place.

This is exactly what scientists do in the How It’s Made episode about yeast: isolate the best yeasts from one vineyard to create wines that truly express its terroir.