Yeast with hop genes
Genetic engineers have taught yeast to hopping beer
Daria Spasskaya, N+1
Bioengineers have created genetically modified yeast that synthesizes the aromatic components of hops – terpene alcohols geraniol and linalool. In the process of making beer with these yeast, hops can not be added, which significantly reduces the cost and simplifies the production process. Double-blind testing of the experimental batch of the drink showed that this beer has an even more pronounced taste and aroma than American ale prepared in the traditional way. A scientific article describing the development of yeast strains and their testing is published in Nature Communications.
Hops give beer its characteristic bitterness and aroma. To achieve the desired taste, hops are added to the wort during the cooking process, and to add flavor – at later stages of the preparation of the drink; this procedure is called beer hopping. There are many varieties of hops that differ in the concentration of aromatic components. However, even within the same variety, there may be a variation in the content of essential oils, and this is one of the reasons why the characteristics of beer can be difficult to standardize.
The aromatic fraction of hops contains many components, but researchers have found that the main contribution to the hopping of beer, at least for varieties popular among American brewers, is made by two molecules from the terpene class – geraniol and linalool. These substances are formed from a single precursor with the participation of two different enzymes-synthases.
Bioengineers from the University of California and the Institute of Bioenergetics in Emeryville (USA), in collaboration with the California brewing company Lagunitas, have developed a technology that allows hopping beer without using hops. To do this, the genes of geraniol and linalool synthesis enzymes were embedded in the genome of an industrial yeast strain used in brewing. In addition, researchers have learned to regulate the expression of these genes in order to change the taste of beer in a targeted way.
Since the enzymes involved in the synthesis of these terpenes have not yet been identified directly in hops, scientists have tested several genes of linalool and geraniol synthases from other aromatic plants. It turned out that a sufficient level of activity in yeast cells for these two substances is shown by a shortened version of an enzyme from mint and a full-sized enzyme from basil. In order to ensure the synthesis of the terpene precursor, bioengineers also had to overexpress several yeast enzymes of their own. To integrate genetic cassettes into yeast DNA, the researchers used the CRISPR-Cas9 system.
To test the new technology in practice, the authors of the work prepared with each of the strains a small experimental batch of beer without the use of hops. Cascade hops from five different American farms were used to prepare control "traditional" batches. Beer comparison showed that the use of hops from different places leads to a variation in terpene concentrations, and, consequently, to variations in the taste of the drink. At the same time, the use of modified yeast gave a more stable result.
In the final experiment, the researchers prepared American ale according to a classic recipe using "dry hopping" technology, when hops are added to beer already at the fermentation stage, or with genetically modified yeast. The tasters in the double-blind testing did not notice a significant difference between the presence or absence of "dry hopping", however, the experimental beer prepared with modified yeast clearly had a hoppy aroma.
Left: comparison of the severity of the "hop component" of beer prepared using the parent strain WLP001 or with its three genetically modified derivatives (JBEI). On the right: comparison of beer made with dry hopping technology (ID dry hop) or without it (WA dry hop) with beer made using a modified strain of JBEI. An asterisk indicates a statistically significant difference. Charles M. Denby et al / Nature Communications, 2018.
The researchers admit that the most complete flavor bouquet of the drink can be achieved at the expense of other aromatic components of hops. Nevertheless, the proposed technology of genetic modification of yeast allows you to add the necessary synthesis pathways to industrial strains, and thus complement the taste of beer.
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