University of California, Berkeley (UC Berkeley) biologists have engineered
strains of brewer's yeast that not only ferment the beer, but also provide
two of the prominent flavor notes provided by hops. Yeast is preferred
instead of hops because growing hops uses lots of water, not to mention
fertilizer and energy to transport the crop, all of which could be avoided
by using yeast to make a hop-forward brew. A pint of craft beer can require
50 pints of water merely to grow the hops.

The engineered yeast strains were modified using the gene editing tool
CRISPR-Cas9. Charles Denby and Rachel Li from UC Berkeley inserted four new
genes plus the promoters that regulate the genes into industrial brewer's
yeast. Two of the genes - linalool synthase and geraniol synthase - code for
enzymes that produce flavor components common to many plants. In this
instance, the genes came from mint and basil, respectively. The two other
genes were from yeast and boosted the production of precursor molecules
needed to make linalool and geraniol, the hoppy flavor components.

The researchers used a specially designed software program to get the right
mix of promoters to produce linalool and geraniol in proportions similar to
the proportions in commercial beers produced by Sierra Nevada Brewing
Company. They then asked Charles Bamforth, a malting and brewing authority
at UC Davis, to brew a beer from three of the most promising strains, using
hops only in the initial stage of brewing to get the bitterness without the
hoppy flavor. Hop flavor was supplied only by the new yeast strains. In
double-blind taste tests, employees of Lagunitas Brewing Company in
Petaluma, California, characterized beer made from the engineered strains as
more hoppy than a control beer made with regular yeast and Cascade hops.

[news.berkeley.edu]