What to Do About Butyric Acid Beer Off Flavor

We have all been there. You take that first bite of food, or that first sip of your drink, and something is just… off about it. Sometimes the off flavor is obvious. You can tell it’s gone bad. Other times, it is not so clear, and you take another bite, another drink. You lower your nose to smell the offender. You can’t quite place it. But one thing is for sure – this was not the flavor you expected. It can be troubling when you get an off flavor, especially in something you might be tasting for the first time. Is that flavor supposed to be there? With beer today, it can be really tricky because such a wide variety of beers exists, and some are meant to taste wildly different from what we expect. Watermelon beers and cucumber beers, even intentionally sour brews will have us second guessing ourselves.

Among brewers, the most common offender when something is just not right is butyric acid beer off flavor.

What Is Butyric Acid Beer Off Flavor?

Butyric acid tastes and smells like baby vomit. It sounds gross, but it’s true. If you have not had the unfortunate experience of tasting this strong flavor, count yourself lucky. Just know that it may still be in the cards for you. It is a common mishap in brewing, and it sticks with you for life once you’ve tasted it.

Butyric Acid

Butyric acid is actually an important flavor component in food and beer. It is a fatty acid created when good bacteria break down (typically) dietary fiber. Butyric acid is found in animal fats, plant oils, and in your gut (which is why the vomit reference is made so often). A short chain fatty acid, or SCFA, butyric acid is good for you as it provides your colon cells with energy, helping aid in the digestive process. Indeed, scientists are currently studying the health benefits more extensively to figure out if some humans with conditions like irritable bowel syndrome and even colon cancer may benefit from butyric acid supplements.

Butyric Acid off flavors 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 flavors in your favorite brew. The problem only arises when there is too much butyric acid in beer.

Starch Slurry

During the brewing process, butyric acid, also referred to as butanoic acid, is produced by anaerobic bacteria such as Clostridium butyricum during glucose fermentation. Basically, Clostridium infects the beer when the starch slurry during glucose syrup manufacturing is mishandled. It has also been shown to grow in excessive amounts during the wort process.


Wort is the bittersweet sugar solution created when the malt is mashed and boiled with the hops. The yeast then ferments that solution and makes beer.

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Somewhere along that line, it is thought, the wort can go wrong and produce too much butyric acid, resulting in that less than desirable moldy cheese, or vomit, smell and taste.

Plant Hygiene

Bottom line, proper plant hygiene is essential to avoiding the butyric acid beer off flavor. It seems that something is happening at the plant level, either with the malted grain or the hops, that is then revealed during the conversion of the plant starch to sugar. Brewers will have to take care to have regular and strict quality control measures in place to avoid losing a batch of otherwise top-quality brew to butyric acid beer off flavor.

Avoid Butyric Acid Beer Off Flavor

The most common recommendations to avoid this problem in addition to quality control is to maintain strict sanitation measures that will inhibit the entry of Clostridium into your brewery and to consider whether you want to engage in CO2 purging, which may encourage butyric acid formation.

But… Sour Beer?

Right. On the one hand, we want to avoid that awful baby vomit smell and flavor in beer. On the other hand, many beers today are intentionally made to be sour. What, you might be asking yourself, is happening?

Sour beer has an intentionally acidic, tart, or sour taste. Lambic is one example. German gose is another. These beers are made by allowing wild yeast strains and bacteria into the brew, traditionally through leaving the wort out in the open air.

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Today, most sour beers you’ll find on market shelves are made through the addition of fruit, which contributes to citric acid in the beer.

Risky Business

Sounds risky? That’s because it is. Any time we play with bacteria, there are risks involved. One form of mold might form penicillin. Another might be a deadly spore. Plants are unpredictable, as are the bacteria that thrive upon them. Most producers of sour beer have gained expertise in the field and have practices that go back decades, if not over one hundred years.

Thus, sour beers might be on the rise in popularity, but not just anyone can make them, and not just anyone should. The last thing you want is to make a name for yourself and your brewery in the wrong way, by getting people sick, either with sour beer or too much butyric acid. Maybe leave the bacteria experimentation to other, less risk averse brewers.

Keep It Clean

Today, it is a simple step in your brewing process to simply keep a clean brewery, oversee the hygiene of the plants you use in your brew, and keep quality control measures in place.


Are you still pitching fresh yeast every time? By reusing your yeast, you can save up to hundreds of thousands of dollars per year on just yeast alone!

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  1. D. B. Hawthorne, R. D. Shaw, D. F. Davine, T. E. Kavanagh & B. J. Clarke (1991) Butyric Acid Off-Flavors in Beer: Origins and Control, Journal of the American Society of Brewing Chemists, 49:1, 4-8, DOI: 10.1094/ASBCJ-49-0004
  2. Anna Dysvik, Sabina Leanti La Rosa, Gert De Rouck, Elling-Olav Rukke, Bjørge Westereng, Trude, Microbial Dynamics in Traditional and Modern Sour Beer Production, DOI: https://doi.org/10.1128/AEM.00566-20


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