Upright's Amazing Apparent Attenuation

Last night, Upright held a press event at the brewery to celebrate their first anniversary and launch of two celebratory beers. (Reviews to come.) Press events, for those of you who haven't had the pleasure, generally follow a pretty standard script: a pour of beer upon arrival, a tour of the brewery and subsequent pours, and all the while Q&A as things progress. I find that the questions generally elicit the most fascinating information, and so it was last night, when Upright's Alex Ganum talked about how finicky his yeast is.

Alex uses a French farmhouse yeast strain, and these are notoriously difficult to work with. The most famous, and famously difficult, is Dupont's, which requires high fermentation temperatures (over 85 degrees; regular yeasts do better below 70) and then craps out before it's fully done, requiring a brewery to nurture and coax it along for days or weeks. Alex's isn't as bad, but it bears some of these hallmarks. He ferments it in the mid-70s, and then has to wait while it meanders along--sometimes for three weeks in the open primary fermenters. Other yeasts would take less than a week. But even then, the fun's not over. Once it goes into the tank, the beer keeps evolving.

Alex knew the yeast was efficient even a year ago when I first visited the brewery; it's attenuation was on of the attractions. After a year of working with the beer, though, he's started to realize that it may be too much of a good thing. Because those yeasts keep munching, he can't bottle or keg for a long while without worry of foamy pints or explosive bottles. He prevailed on the Widmers to do a lab analysis for him (which they happily did, and gratis, contrary to the suspicion some hold that they wish to crush the competition) and the results were shocking. Upright's beer was reaching levels of attenuation in the mid-90s, sometimes as high as 97%.

What is attenuation, and why is this remarkable? Let's start with the science. Here's White Labs, a commercial brewers yeast company:

Yeast consume the sugar in wort, and turn that sugar into CO2, alcohol, and flavor compounds. When yeast finish the fermentation process, they shut down, clump together, and fall to the bottom of the fermentor, or "flocculate." When yeast flocculate, it is easy to see that fermentation is done. But how can the brewer be sure? What if the flocculation is minimal, and yeast and CO2 stay in solution. How does the brewer really know when fermentation is done? The answer: by testing the degree of attenuation. Apparent attenuation percentage is the percentage of sugars that yeast consume. Attenuation varies between different strains. The fermentation conditions and gravity of a particular beer will cause the attenuation to vary, hence each strain of brewers yeast has a characteristic attenuation range. The range for brewers yeast is typically between 65-85%.

Typical ale yeasts are comparatively inefficient. The kinds of beers most appreciated in Beervana will have an attenuation of around 70%, give or take. Lager strains are roughly the same. Most Belgian strains--wild yeast excepted--are more attenuative, but still, few get out of the high 70s. So, a beer with an apparent attenuation of 97% would have almost no residual sugars.

Alex's yeast is the Energizer bunny--it just keeps going. As a homebrewer and craft beer fan, I find this charming. So farmhousey! But I imagine it's driving Upright crazy. For one thing, it costs a lot of money to let beer just sit in a tank. If it takes a beer twice as long to finish fermenting, a brewery can only produce half as much beer per tank. Beyond that, Upright can't risk letting any beer but the most bone-dry out of the brewery for fear that it will continue to ferment in kegs and bottles. From a business perspective, you want predictable and fast, not idiosyncratic and farmhousey. Charming is not a prized characteristic in the behavior of yeasts.

On the other hand, the yeast produces some amazing beer. The Four Play, in particular, really benefits from this strain, for reasons I'll mention in my future review. Most beers with this kind of attenuation would taste thin and bone dry, but somehow the production of esters counteracts the dryness. And how the beer remains creamy and silky--never thin--is a mystery to me. Chemists out there, please weigh in.

When Alex founded Upright, he wanted the beer to be marked by the character of the yeast and the qualities of farmhouse brewing--local ingredients, handmade beer, idiosyncratic styles, and a flavorful rusticity. A year in and he and co-brewer Gerritt Ill have managed to pull this off. I wonder if sometimes they feel this yeast is punishing them for their success. Ah brewing!
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