Making Better Biofuels, from Beer Broth

June 28th, 2012 by Tina Casey

Cornell researchers have figured out a way to make biofuel products from beer broth, and their findings are so exciting that the normally unflappable Royal Society of Chemistry has conferred “hot” status on a paper describing the beer-to-biofuel process. The beer broth in question isn’t suitable for tippling, which makes it a little less exciting to some of us, but it could lead to a low-cost method for producing high-value biofuel precursors.

A Beer Broth Primer

Like beer, ethanol is produced by microbial digestion in the form of yeast fermentation. In the two-step process, starches like cornstarch are converted to sugar by enzymes, and then the sugar is converted to ethanol by yeast.

According to writer Anne Ju of Cornell, the fermentation broth for ethanol is identical to that of beer in terms of its chemistry, which is why the ethanol industry calls it “beer broth,” except that for a variety of reasons you would not want to drink it.

Ethanol is water-soluble, so the next step to producing fuel is to separate ethanol from the water in the beer broth. This distillation process is energy-intensive, and it is a main reason why the cost of ethanol fuel relatively high.

A Step Toward Low Cost Biofuel

The Cornell team approached the problem from the perspective of creating an oily, non-soluble fuel precursor in beer broth that could be separated from water without undergoing expensive distillation.

Using donated beer broth from a nearby corn ethanol plant, they tailored the community of microbes in the broth to draw the fermentation process out to a series of steps.

The end result was a fuel precursor called caproic acid, a fatty acid that occurs naturally in some animal fats.(Another name for caproic acid is hexanoic acid, referring to its derivation from hexane, which is a constituent of gasoline).

The tricky part was to get the pH and temperature into the right range, to prevent the microbes from shifting over to methane production.

What Now, Beer Broth?

According to Ju, the process can be integrated easily into existing ethanol production facilities. However, researchers used 5-liter tanks for bioreactors, which is quite a bit smaller than the massive commercial scale tanks used in the ethanol industry. Scaling up will be the next hurdle.

Now that the concept of tailoring beer broth communities has been proven, the team also expects to be able to create communities of microbes that produce other products, too.

A Bioeconomy Role for Beer

While we’re on the subject of beer, it’s worth nothing that drinkable beer has been starting to play a role of its own in the emerging bioeconomy, which President Obama recently expressed as the National Bioeconomy Blueprint for transitioning the U.S. out of fossil fuels and petrochemicals.

Noted microbrewery Karl Strauss got a jump on things a few years ago, when it started up a venture to convert its waste yeast to ethanol.

At the mega-brewery end of the scale, AB-InBev (formerly Anheuser Busch) recently partnered with Blue Marble Bio to convert brewery waste into carboxylic acids (fatty acids used in soap making, among other things) as well as biogas.

Image: Some rights reserved by Greencolander.

Follow me on Twitter: @TinaMCasey.









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