Biologists at the University of California, Berkeley have used CRISPR technology to create a hop-free brew that still has all the flavor and aroma of conventional beer. By replacing the hops with strains of genetically-engineered yeasts, the researchers hope to not only reduce the cost of a pint, but make it more environmentally friendly in the process.

Humulus lupulus, better known as hop, is the climbing hop plant whose flower has been used for over 1,200 years by brewsters to stabilize beers while infusing them with their characteristic bitter or citrusy flavors and aromas. This is all well and good, but hops can be expensive to cultivate, is often harvested by hand, and requires a lot of water – 50 pints (23.7 liters) for every pint of beer. In addition, the quality can vary from harvest to harvest, and a bad year can lead to hop shortages.

To help overcome these problems, Charles Denby, Rachel Li and their team from Berkeley Brewing Science looked at how hops flavors beer and concluded that similar – and more consistent – results could be achieved by using a genetically modified yeast instead.

The new yeast strains were created using CRISPR-Cas9 genome editing technology based on a genetic sequence used by bacteria for self-defense. By introducing two genes, linalool synthase and geraniol synthase, from mint and basil respectively, along with promoters from other yeast strains to regulate the genes, a new strain of yeast could be made to produce linalool and geraniol, which are the elements that deliver the hoppy flavor.

To achieve this, the scientists used the Cas9 gene to cut the host DNA and insert the desired sequences before healing the strand with enzymes. A bespoke software program helped the team to keep the two flavors in the proper proportions using beers made by the Sierra Nevada Brewing Company as a guide.

The researchers say this was no easy matter because where laboratory yeasts have one set of chromosomes, brewer's yeast has four. This meant having to introduce the new sequences four times over to create a stable strain that would continue to propagate with the new genes intact. In addition, the team had to scale up production from test tubes to 40-liter (10.6-gal) kettles

When the yeast was ready, Charles Bamforth, a malting and brewing authority at UC Davis, brewed a special batch of beer using hops only at the very start of the process, so it wouldn't impart a flavor to the wort. The yeast was then introduced. Meanwhile, an identical batch using standard hops and yeasts was brewed as a control. A blind comparison taste test with 27 brewery employees was then conducted with surprising results.

"This was one of our very first sensory tests, so being rated as hoppier than the two beers that were actually dry-hopped at conventional hopping rates was very encouraging," says Li.

The research was published in Nature Communications.

Source: UC Berkeley

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