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Science of Beer: Tapping the Power of Brewer’s Yeast

on 31/03/14 at 2:15 pm


imagesBeer is one of the world’s oldest beverages, dating back thousands of years to ancient Egypt and Iraq. People drank it for centuries, but never really understood the chemistry of what turned its ingredients to alcohol.

“When it went well, it was attributed to the beer god,” said Jim Withee, a genetic scientist and CEO of GigaYeast, a Belmont company that sells yeast to brewers. “And when it went poorly, it was attributed to beer witches.”

The secrets of successful beer don’t come from witchcraft, but from brewer’s yeast, or Saccharomyces cerevisiae: a microscopic organism that has fascinated Withee for decades. It’s integral to fermentation, the chemical process that transforms ordinary water boiled with grains into a tasty beverage.

“You take a sweet extract from grain, and over time it’s converted into a beverage with all kinds of amazing flavors and ethanol and CO2,” said Withee.

With giant tanks looming in his Belmont facility, Withee and his staff produce large batches of liquid yeast for his customers — like Malcolm McGinnis, a co-founder and brew master for Freewheel Brewery Company in nearby Redwood City. (You can see him at work in the video and learn more about Freewheel in this interview at KQED’s Bay Area Bites food blog.)

“Yeast that’s sold to people that make wine and spirits and beer comes in two basic forms,” said  Withee. “There’s liquid yeast and there’s dried yeast. Both of them are alive and active. Liquid yeast is exactly what you would think it is. It’s a live culture that’s grown up and concentrated into a wet slurry.

“Dried yeast is also alive,” he added. “But it’s grown up as a liquid culture and then it’s dried in such a way that it actually is still alive even though it’s dried down, much like the baking yeast you probably use at home if you ever make bread. The water is extracted from it at a very low temperature and under very low pressure, so the yeast stay alive.”