Author: Malcolm Frazer

Ever drink a beer, either commercial or homebrew, that tasted of baby vomit or rancid cheese? If so, then you’re likely acquainted with the off-flavor of focus for this xBmt. Butyric acid is produced by various types of bacteria as a metabolic byproduct and is perceptible by most people in rather low amounts, though some is present in nearly all fermentations, just not enough to be noticed. When it comes to clean beer styles, butyric acid is ubiquitously accepted to be an offensive off- flavor and indicates a contamination occurred. However, there’s some evidence that certain strains of brettanomyces have the ability to convert small amounts of butyric acid into ethyl butyrate, which is lauded for imparting tropical fruit and ripe pineapple character (check out the Milk The Funk wiki).

Since this is an off-flavor series, we were interested in the abilities of tasters to detect butyric acid when used to intentionally dose a clean beer. Is it really as easy to detect as we’ve been led to believe, or will blind tasters even notice their beer has been dosed with a presumably vomit tasting chemical? I was pretty excited to test this one out!

Cheers to FlavorActiV for providing us with the concentrated butyric acid flavor standards for this xBmt!

| PURPOSE |

To evaluate the ability of blind tasters to distinguish between a pale lager dosed with butyric acid flavor standard from an unadulterated sample of the same beer.

| METHODS |

In order to keep me blind to the off-flavor for my own trials, all identifying labels were removed by Marshall from the flavor standard packaging. For this go-round, I used the champagne of beers, Miller High Life, in hopes its delicate character would allow the off-flavor to take center stage.

According to FlavorActiV, the approximate flavor threshold for butyric acid is 2-3 parts per million (ppm) with most commercial beers clocking in at 1.5 ppm or less. Given Miller’s arguably precise and clean process, High Life presumably falls on the lower end of the butyric acid scale, though we were unable to find any lab data confirming this hunch.

Each butyric acid capsule provided by FlavorActiV is designed to impart 3 times the flavor threshold when added to 1 liter of beer, the recommended concentration for off-flavor training. To prepare the dosed sample, I followed the instructions provided by FlavorActiv by first gently pouring about 200 mL of beer into a standard 4 liter pitcher, adding the contents of 2 flavor standard capsules, gently swirling, then adding an additional 1800 mL of beer to the vessel. The non-dosed samples were treated similarly to ensure no differences caused by anything other than the off-flavor.

| RESULTS |

Data for this xBmt was collected during a TRUB Homebrewers meeting being held at Voodoo Brewery. In total, 16 people with varying levels of experience, all blind to the variable, were served 1 sample of the beer intentionally dosed with butyric acid flavor standard and 2 samples of the clean beer in different colored opaque cups then instructed to select the unique sample. In order to reach statistical significance, 9 tasters would have had to select the dosed sample, which is exactly how many made the correct selection (p<0.05; p=0.049), suggesting participants were able to reliably distinguish a beer intentionally dosed with butyric acid from a clean sample of the same beer.

Those participants who correctly selected the dosed beer as being different were instructed to complete a brief set of additional questions comparing only the two different beers, still blind to the nature of the xBmt. When the 9 tasters who correctly identified the unique sample on the triangle test were asked about preference, 8 chose the non-dosed sample while 1 person apparently enjoyed the cheesy character of the adulterated beer.

It was then revealed to participants that one of the samples had been dosed with an off-flavor, though they were not informed which off-flavor was used. When asked to identify the beer they believed was dosed with an off-flavor, all 9 tasters made the correct selection. Next, tasters were provided a list of common off-flavors that included brief descriptions of how they typically manifest in beer and asked to select the one they believed the beer was dosed with– 3 tasters correctly identified the off-flavor as being butyric acid, 2 thought it was isovaleric acid, which is commonly mistaken for butyric, 2 felt it was DMS, 1 chose diacetyl, and 1 believed it was lightstruck (the same person who reported preferring the beer dosed with butyric).

My Impressions: Since I was unaware of the particular off-flavor being used for this xBmt, my trials were more blind than usual, and I’m pretty sure having a newborn in the house gave me a bit of an upper hand on this one. Over the course of multiple triangle tests, I was able to consistently identify the unique sample, as the dosed beer had what us judges are trained to parrot as baby vomit or stomach acid. When I let Marshall know I was finished collecting data, he asked if I had an idea of what the off-flavor was and I responded confidently that it was likely butyric acid. Thanks, Marshall…

| DISCUSSION |

Butyric acid is one of those off-flavors that smells like what it makes me want to do, and the fact tasters in this xBmt not only were able to reliably distinguish a beer intentionally dosed with it from a clean sample but strongly preferred the non-dosed beer is admittedly somewhat promising. I’m not really sure what to think about the 1 correct taster who reported preferring the butyric beer, I’m compelled to believe it was an error, but who knows, preference is subjective and they were presumably able to tell a difference.

I judge in a lot of competitions, which means I taste a lot of homebrewed beer, some that have occasionally had what I perceived to be characteristics of butyric acid. While there are times my perceptions don’t always align perfectly with the people I’m judging next to, it’s been my experience that the puke-like aroma of butyric acid tends to be fairly consistent between judges, usually only getting confused with the other cheesy off-flavor of isovaleric acid. Regardless, if you end find yourself in possession of a score sheet with comments indicating butyric acid, it may not be a bad idea to consider the potential vectors for contamination in your setup, as it’s possible a bug of some sort is finding its way into your beer.

If you have any thoughts about this xBmt, don’t hesitate to share them in the comments section below!

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