Researchers discover new methods to fight invasive yeast in red winemaking

New research from Washington State University scientists has revealed better techniques to fight a barrel-dwelling spoilage yeast that has frustrated winemakers for decades.

An article recently published in the American Journal of Enology and Viticulture (AJEV) and the South African Journal of Enology and Viticulture journals found three methods to sanitize oak barrels to prevent Brettanomyces bruxellensis, or “Brett” for short. These include using steam, warm wine, or warm water.

“This yeast causes all kinds of consternations in red winemaking,” said Charles Edwards, professor and food scientist in WSU’s School of Food Science.

Once Brett makes its home in red wine oak barrels, it can be nearly impossible to remove due to the porous nature of oak.

For this study, Edwards and his team looked into how Brett affects wine quality and how to provide winemakers tools to prevent or cure infections in their oak barrels.

“The question we had before us was, is it possible to sanitize oak barrels and protect the wine from Brett?” Edwards said.

This particular species of yeast can cause pungent aromas in wine, with smells similar to a barnyard, Band-Aids, or even a metallic taste. While too much Brett is not good, smaller amounts can add leathery, spicy notes to wine, which are sometimes considered good flavors.

As part of their research study, Edwards and his team filled several 16-liter barrels of wine, added Brett, and allowed the microorganism to flourish for several months.

Once enough time had passed, Edwards and his team spent a few days at his wood shop, breaking down the barrel into small wood staves to analyze the wood and figure out how deeply Brett can become embedded in the oak.

Zachary Cartwright, a recent PhD graduate who worked on the project, took the wood samples to the Scanning Electron Microscope (SEM) lab in Pullman to see how far the Brett cells had infiltrated the barrel wood.

The industry standard is to steam clean a barrel for three to five minutes if it’s suspected of having Brett, said Cartwright, who now works at Meter Group in Pullman as a Lead Food Scientist.

“What we’re finding is that infected barrels need to be steamed for much longer, about 10 to 12 minutes,” he said.

Edwards said this new research shows that temperature and time are bigger factors than once thought.

“The steam has to be hot enough to pass through multiple layers of wood to reach where the microorganism is, otherwise you’re just sanitizing the inner layer of the barrel,” he said.

The steam and water need to be hot enough to permeate multiple wood layers and destroy Brett, while using wine to sanitize barrels doesn’t require as much heat, due to ethanol being present in the wine.

Edwards said the big takeaway message is that wine barrels need to be heated more to get rid of Brett. “We have to be more analytical in our approach. There is still a risk of spoilage, but it’s a question of lowering the risk,” he said.