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Is Agricultural Waste the New Plastic?

November 20, 2012

Category: A Closer Look

Yeast is an essential ingredient in the beer brewing process. But after it serves its purpose during fermentation it leaves behind waste sediment, and it’s hard to come up with ways to recycle it.

Stumped with a sustainable answer to its yeast-waste, Sierra Nevada Brewing Company collaborated with researchers at nearby Chico State. The result was a research project that showed promising results in using agricultural waste as a means to create a biodegradable plastic.

“Yeast sediment serves as a medium for bacteria to produce lactic acid, which can be purified and made into biodegradable plastic,” said Chico State biochemistry professor Larry Kirk, who is part of the ongoing project.

In 2008, Kirk joined Chico State biology professor Larry Hanne and engineering professor Joe Greene on the project, which was supported by Chico’s Sierra Nevada Brewing Company as well as a grant from the CSU’s Agricultural Research Institute (ARI).

The project immediately garnered national recognition. In 2009, Chico State students working on it took first place in the CSU’s Student Research Competition, and presented their poster at a national research competition in Washington, D.C.

Three years later, Kirk says the ongoing project has “proved its point” and is moving onto the next stage.

“We proved that we were able to cultivate lactic acid from the bacteria,” Kirk said. “However, it was difficult to get bacteria to grow in the spent yeast we obtained from Sierra Nevada.”

Unfortunately for the Sierra Nevada project, brewers have worked on avoiding bacterial growth in beer for centuries. Hops—the beer ingredient that gives ale its bitter, tangy flavor—also has antibacterial compounds. Hops residue remained in the yeast, so the lactic acid-producing bacteria were unable to thrive.

But fortunately for the research project, Kirk says the same method can be applied to different types of agricultural waste. He says the project is now looking into ways to develop methods to isolate lactic acid from the bacteria obtained from rice hulls.

“It wouldn’t be research if it wasn’t trial and error,” said Kirk. “We learned the best way to cultivate the lactic acid bacteria. We know it can still be done with a hops-resistant bacteria strain, which are becoming more prevalent in brewing.”

For the immediate future, Kirk says he hopes they will soon move on to making the biodegradable plastic from the rice hull lactic acid. It would be more sustainable than today’s biodegradable plastic, which is made from corn starch.

“We want to make it from waste material, then it will be truly ‘green’,” Kirk said. “With Chico State and the local region so focused on sustainability efforts, I believe we’re in the right environment to get that done.”

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