This is the second part of a series on the funky little yeast called Brettanomyces . Be sure to check out the first part of this series for a general overview of Brettanomyces in beer.

Brettanomyces yeast are survivors. Slow and steady is their motto. They don’t grow very quick, and are easily out-competed by other yeasts. They can survive just about anywhere there is water, and they can metabolize a wide range of compounds to use for energy. It is the by-products of these metabolic processes that produce the flavors we associate with Brett, and a few of these flavor compounds in particular are of great importantance.

The compounds 4-EP (ethyl phenol) and 4-EG (ethyl guaiacol) are truly the Jekyll and Hyde of Brett flavors. Generally produced together as a product of Brett metabolizing several naturally occurring acids in beer, each compound has its own characteristic flavor. When smelled on it’s own, 4-EP comes across as smelling like band-aids or anti-septic - definitely negative flavors. 4-EG, on the other hand, comes across as smoky, bacony, or spicy, and is generally viewed as a positive taste. Brett will produce much more EP then EG normally, with a ratio of 8 EP to 1 EG being common. However, our noses are much more sensitive to 4-EG, so these flavors tend to balance out.

This 8 EP to 1 EG ratio, while most common, is not set in stone. Many studies of been done on these compounds in the wine world, examining wines with ratios of 3:1 all the way up to wines with a 30:1 ratios. The smaller the ratio, the more pleasurable your average taster would view the Brett flavor characteristics. Wines with 3:1 or 4:1 ratios are typically described as being smoky or spicy, while wines at the higher end of the ratio are described as medicinal or barnyard. The exact factors that influence these ratios are unknown at this time. I don’t think it is a stretch to consider that the EP to EG ratios also have a big influence on the flavor profiles of Brett beers.

The other major flavor component of Brett beers is Isovaleric acid. A by-product of Brett’s metabolism of various proteins, Isovaleric acid has a cheesy flavor that is also sometimes described as rancid or vomit. At times, Isovaleric acid can seemingly dominate the other Brett flavors in a beer or wine.

The very interesting thing about Isovaleric acid is that humans are variably sensitive to it. While everyone can taste it, the levels we can detect it at vary dramatically from person to person. We’re talking about a variance of several orders of magnitude here. Our varying ability to taste Isovaleric acid may be the reason why Brett flavor is so polarizing to people - those of us who enjoy the Brett flavor in beer may simply not be getting the same negative impact from Isovaleric acid as the sensitive tasters are.

There are other compounds released by Brett, such as 4-EC (ethyl catechol), that help round out the Brett flavors in beer, but are not nearly as prevalent flavor-wise as the ones we’ve already discussed.

The next post in this series will be a quick discussion of how Brett is being used in beer along with recommendations for aging Brett beers.

Jason

jason@brewbasement.com

www.brewbasement.com