The pursuit of hoppiness

In 1487, the German duchy of Munich adopted a law that insisted the only permissible ingredients for making beer were water, barley and hops. The law was introduced to the rest of Bavaria in 1516 and then embraced later still by greater Germany.

It is called the Reinheitsgebot and has been regarded as a credo by fundamentalist brewers around the world ever since.

Now, however, a team of scientists led by bioscientist Jay Keasling from the University of California, Berkeley, in the US, is suggesting that the Reinheitsgebot might actually be a bit too complicated and the interests of good beer might be best served by dropping the hops altogether.

This news, of course, will send a collective cry of “mein Gott!” around the globe, but Keasling and co base their argument on the one crucial ingredient on which the German code is silent – yeast.

There is a very good reason for the absence of the world’s most useful fungus from the Reinheitsgebot. At the time, no one knew of it, much less of its crucial role. As every ale aficionado today knows, brewer’s yeast (Saccharomyces cerevisiae) gobbles up simple sugars such as glucose and maltose and produces carbon dioxide and alcohol.

In a paper published in the journal Nature Communications, Keasling and his colleagues show that with a little tweaking it can also produce the bitterness and flavour long associated with hops.

In beer-making, the word “hops” denotes the flowers of a herbaceous perennial plant called Humulus lupulus. There are scores of different varieties, bred obsessively by brewers to impart specific blends of bitterness and flavour to what might be otherwise rather bland drinks.

Hops, however, are energy and water intensive to grow. They are also notoriously troublesome, in that they do not breed “true” – that is, a seed from a plant will not produce an identical offspring, meaning that commercial crops must be effectively cloned from cuttings.

Keasling’s team has found a way to avoid all these problems by ditching them completely and instead engineering the genome of the yeast to produce hoppy characteristics. They do so by altering commercial S. cerevisiae DNA, adding snippets derived from other yeasts and herbs such as mint and basil.

Doing so, they report, involves a “unique challenge” and requires “state-of-the-art engineering techniques”.

The result, however, is a yeast that is able to biosynthesis aromatic molecules that impart hoppy flavours – and does so better than hops.

“Beers produced using these strains are perceived as hoppier than traditionally hopped beers by a sensory panel in a double-blind tasting,” they conclude.

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