Five years ago, Dr. Jim Withee made a calculated decision and quit his high-paying job as a government scientist to help people drink good beer. Withee had studied yeast in graduate school and applied his findings to the human immune system, studying ways for the body to accept organ transplants and fight diseases like cancer and sickle cell. Over a beer with a brewer buddy at a bar in Shanghai, Withee decided to repurpose his schooling and found GigaYeast, Inc.

The company, which relocated earlier this month from Belmont to a spacious lab in San Jose, now handles fermentation and yeast for more than 300 commercial breweries, including the award-winning Sante Adairius, which is one of many craft beer icons demanding GigaYeast’s exceptional microbes.

“It’s the oldest biotechnology,” Withee says. “Sometime around 10,000 years ago, humans all over our planet started harvesting microbes and reusing them over and over. We still can’t make wine or beer or spirits or any of the other thousands of fermented foods or beverages without live microbes doing all of the work.”

Yeast is a fungus that grows almost everywhere and preserves everything from Korean kimchi to Italian sausage to Belgian beer. The earliest brewers didn’t understand the metabolism that occurs as yeast munches on sugar and excretes ethanol and other flavor-laden compounds. But they knew they liked beer, and they wanted more.

“Fathers would pass [yeast] down to sons in little urns saying, ‘Put it in this one, it comes out really good. Everything else tastes like shit,’” Withee says with a laugh. “And what they were doing was selecting over and over for very particular traits you don’t find in wild yeast. So what we’re left with now are these strains that have been highly selected for hundreds, sometimes thousands of years.”

Occasionally, a batch would spoil. The unscientific brewers blamed this on beer witches. To ward them off, they burned incense and placed protective totems nearby their fermenting vats. Thirty-nine hundred years ago, an early Mesopotamian jotted down a hymn honoring Ninkasi, the goddess of beer, in hopes for a tasty brew—one of the first examples of writing.

At the turn of the 20th century, fermentation similarly fascinated scientists. Their studies confirmed yeast’s necessity for fermentation, but they also learned that batches spoiled when they were contaminated with bacteria—a finding that Louis Pasteur would extrapolate into his germ theory of disease.

“It’s really easy to grow microbes of any type,” Withee says. “You’re probably doing it in your refrigerator right now if you haven’t cleaned it out in a while. But what we do is hard because we need to produce large quantities of a very pure culture that’s uncontaminated with anything else. The ideal growth conditions are the same for lots and lots of microbes that can contaminate.”

Like human beings, yeast needs proteins, sugars and nutrients, and prefers temperatures between 65 and 80 degrees Fahrenheit. The yeast spawn new generations every couple of hours and have a species diversity that rivals canines. Gigayeast stores their batches in cryogenic freezers—the same type keeping Walt Disney on ice—then thaws them to grows a 4,000-liter  culture from a single cell. Employees check the batches about 25 times from start to finish to ensure there’s no contamination.

“Over the course of a week of growth, you have [hundreds of] generations,” Withee says. “That population can evolve on you and that can be bad. You might get stuff you don’t want. But they’re tested constantly. They’re grown in a sterile environment. It’s kind of a challenge, but we’ve gotten very good at it.”

The timing coincides with a craft beer industry now in its eighth consecutive year of double-digit growth. Withee sees the movement as part of a desire to reconnect with our local artisans.

“Look at it like this: 200 years ago, there were about 4,000 breweries in the U.S.,” he says. “Every city had to have a brewer, you couldn’t transfer it long distances. By the ’70s, we were down to like less than 20 (breweries) because of corporatization. And now, we’re back up to 4,000. A big segment of our population is finally saying, ‘Fuck this, I don’t want to buy things from a big faceless corporation. I want to get it from John down the street.’”