Et tu, Brut IPA?

The Brut IPA - owing to its refreshing dryness, champagne-like vivacity, and unobstructed hop flavors- is the next great variation on the beloved staple of the American craft beer movement. The creation of a dryer, much more attenuated beer starts the domino effect, and the finished product is an IPA that seems lively and pure. The result is an expression of the myriad hop sensations that seems displayed on a lucid, crystalline background.

This new style all boils down to attenuation... so what does this measure tell us about a beer?

Yeasts have a certain diet. There are sugars the yeast can ferment, and others that the yeast cannot. Larger sugars are too much for the yeast and remain through fermentation, contributing a good deal to a taster’s overall impression of the finished product.

Much of the considerations of the brewer with regards to alcohol content, perceived sweetness, and dryness is the result of the presence and the amount of fermentable sugars. Yeasts love these simple sugars, and through their metabolism turn them into carbon dioxide and alcohol.

In fact, some yeasts are more attenuative than others. This means either that the organism itself is less picky about its diet or has the ability to consume more of those available sugars. A more attenuative yeast strain will produce a drier, less sweet beer with somewhat less mouthfeel. At the opposite end of the spectrum, struggling to chomp away at what is available, we have a yeast that leaves the finished product with more sweetness and body.

The Brut IPA is characterized by its extreme attenuation, the fermentation of vast amounts of sugars into those sparkling products. And yet, the Brut IPA often uses the same strains of yeast as other IPAs. How then does the brewer accomplish a beer so different than your typical West Coast-style IPA?

The answer lies in the addition of a particular enzyme called AMG (amyloglucosidase, for nerds.) A whole group of enzymes is responsible for the breakdown of sugars. These are very important in brewing but also in a great number of reactions taking place in living organisms, essential for their survival and digestion of foods.

The malt provides enzymes that break down starches into simpler sugars so the yeast can feast, but these enzymes require certain conditions and the attempted yield of these fermentable sugars will always be opposed by some force or another. AMG is added during fermentation and breaks down the bigger carbohydrates into things yeast, all the while they’re already active in their fermentation.

Those bigger sugars being broken down results in less sweetness and more dryness. The yeast’s affinity for those sugars results in a zippy character and pleasant freshness, as well as a touch more booze.

It’s hard to argue with results. Floral, fruity, and other hoppy aromatics come through with remarkable perceived purity, almost rocketing out of the effervescence.  

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