Overview
Butyric acid is a naturally occurring compound that can be found in beer, as well as other fermented foods and beverages. It is created during fermentation when bacteria, such as Brevibacterium linens, convert sugars into acid. This can happen during the brewing process or after the beer is packaged and stored.
When butyric acid is present in beer, it can manifest as an unpleasant, rancid, or “farmyard-like” aroma and flavour. This can be described as a strong, sour, and pungent smell, often likened to baby vomit, sweaty socks, or cheese. In some cases, butyric acid can also create a sour or biting sensation in the mouth and throat.
If you’re lucky enough not to have had the misfortune to experience this strong off-flavour in a beer or your own beer, well done, or count yourself lucky. It’s not a flavour you forget, and it’s definitely one that’ll stick with you for life once you’ve tasted it.
The level of butyric acid in beer can vary greatly, and it is considered a flaw when it exceeds certain levels. For example, the Beer Judge Certification Program (BJCP) states that a beer should not have more than 2 parts per million (ppm) of butyric acid.
If a person experiences a beer with butyric acid, they may find it to be unappealing and may describe it as having an unpleasant or sour taste. Some may even struggle to finish the beer or find it hard to drink. The beer’s aroma can also be quite pungent, it might even make people feel uncomfortable. They may not be able to identify what exactly is causing the bad taste, but they may associate it with the smell of vomit, farm animals or mouldy cheese.
Overall, butyric acid is an unwanted presence in beer and should be avoided. Brewers strive to maintain a sterile environment throughout the brewing process to prevent the growth of bacteria, which can lead to the formation of butyric acid and other off-flavours.
Beer thought: Interestingly, butyric acid isn’t such a problem in beers where Brettanomyces is also present, because that wild yeast can convert the esters to more pleasant tropical-fruit aromas.
What is Butyric Acid’s Off-Flavour in Beer
At concentrations above its flavour threshold in beer, Butyric acid can cause “cheesy” or “baby sick” off-flavours. Abnormal concentrations in beer can arise due to infections by anaerobic* spore-forming bacteria like: Clostridium.
*relating to or requiring an absence of free oxygen, i.e.”anaerobic bacteria”.
Butyric acid tastes and smells like baby sick. If you’ve ever had the misfortune to get a whiff of a milky, wet, baby bib that’s been dropped for a few days, and left to fester, it’s that.
What Causes Butyric Acid In Beer?
So, what is butyric doing in beer, and why does it taste like baby vomit? The truth is, you usually cannot taste the butyric acid in your beer. At least, you would not be able to differentiate it from among the other strong flavours in your favourite brew. The problem only arises when there is too much butyric acid in beer.
Butyric acid is an important flavour component in food and beer. It is a fatty acid created when good bacteria break down (typically) dietary fibre. Butyric acid is found in animal fats, plant oils, and in your gut (which is why the vomit reference is made so often). Butyric Acid is a short chain fatty acid, or SCFA, and is actually good for you. It provides your colon cells with energy, helping your digestive processes.
Avoiding Butyric Acid Infections
The most common recommendations to avoid Butyric infections is quality control and to maintain strict sanitation measures to inhibit the entry of the main cause of infection: “Clostridium”, into your brewery.
Another point to consider in this age of O2-free fermentation and transfers is whether you want to engage in CO2 purging, which may aid the anaerobic bacteria, and actually work to encourage butyric acid formation.