GE yeast makes beer that stays fresh longer + Alcohol tolerance saved human ancestors

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Genetically-engineered yeast produce beer that staves off staleness : . . . Unless you’re slurping it straight out of the brewer’s conditioning tank, there’s a good chance your beer is at least a few weeks old. Unfortunately, we live in a world where beer needs to be packaged, transported, stored, sold and bought before it can be consumed. Throughout that whole process, beer is constantly undergoing certain chemical reactions – and things like light and heat speed these up. The end result is a stale beer, with a more papery flavor and less fizz than a fresh one. In past research, scientists have found that these flavors are associated with an increase in compounds called aldehydes. These are produced during fermentation, and their levels only increase with age... (MORE)

Brewing beer that tastes fresh longer (release): Unlike wine, which generally improves with time, beer does not age well. Usually within a year of bottling, the beverage starts to develop an unpleasant papery or cardboard-like flavor that drinkers describe as "stale." Now, researchers reporting in ACS' Journal of Agricultural and Food Chemistry have engineered lager yeast to make more molecules that protect beer against staling, resulting in improved flavor stability.

Scientists have linked stale beer flavors to aldehyde compounds, such as (E)-2-nonenal and acetaldehyde. Many of these compounds are produced by yeast during fermentation, and chemical reactions during beer storage can increase their levels. Brewers have tried different approaches to reduce levels of these compounds, such as controlling the fermentation conditions or adding antioxidants, but staling remains a problem for the beer industry. That's why Qi Li and colleagues wanted to genetically modify lager yeast to produce more of a molecule called NADH. Extra NADH could boost the activities of natural yeast enzymes that change aldehydes into other types of compounds that don't contribute to a stale flavor, the researchers reasoned.

The researchers used a genetic technique called "overexpression," in which they artificially increased the levels of various genes related to NADH production. With this method, they identified four genes that, when overexpressed, increased NADH levels. The team found that beer from the overexpressing yeast contained 26.3-47.3% less acetaldehyde than control beer, as well as decreased levels of other aldehydes. In addition, the modified strains produced more sulfur dioxide, a natural antioxidant that also helps reduce staling. Other flavor components were marginally changed. This approach could be useful for improving the flavor stability and prolonging the shelf life of beer, the researchers say.



Alcohol tolerance may have saved our ancestors from extinction (release): The ability to process alcohol may have saved humanity's ancestors from extinction, a new book suggests. About ten million years ago, our African ape ancestors were eating fallen fruits on the forest floor - many of which would have begun to ferment and become alcoholic. At the time, ape populations were crashing in the face of competition with monkey species which were able to eat unripe fruit - which apes, like humans, struggle to digest. What seems to have saved at least one line of apes, the book says, was a genetic adaptation that allowed them to process alcohol, meaning they could begin eating overripe fruits. Monkeys are unable to tolerate the ethanol in such fruits, and this new source of calories might have brought apes back from the brink.

The book - "Humans and alcohol: a long and social affair" - looks at the history of our relationship with alcohol, from our evolutionary past to the present.

"Even today we see great apes eating fermented fruit and even drinking palm wine produced by humans," said co-author Dr Kim Hockings, of Centre for Ecology and Conservation on the University of Exeter's Penryn Campus in Cornwall. "It's hard to be certain of why they do this, and this reflects the complex history of our own relationship with alcohol. One interesting point is that the alcohol level in fallen fruit is usually about 1-4% - something like weak beer - yet much of the alcohol consumed by humans today is far stronger than this. As with other substances like salt and sugar, the problem may not be the substance itself but the concentrations we now have access to."

The book says alcohol is often viewed only as a "social problem" or as a means to get drunk - but this overlooks its importance in the social fabric of many human societies both past and present. "Alcohol has played an important role in how humans have used feasting to create and maintain their relationships," said Robin Dunbar, Professor of Evolutionary Psychology at the University of Oxford. "Across cultures and in different time periods, it has consistently been a major part of the way humans socialise with each other. Increasingly, alcohol is viewed as a medical issue, but alcohol abuse is only a small part of a much wider social pattern of alcohol use by humans."

Many other species are known to consume and process alcohol, and the researchers' next goal is to test ethanol levels in wild fruits. The book, co-authored and co-edited by Dr Hockings and Professor Dunbar, draws on expertise from fields including anthropology, archaeology, history, psychology and biology. It is released today (Thursday) in the UK, and on January 5 in the US. To buy a copy, visit the Oxford University Press website.
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