How do you know if beer has bacteria?

Answered by Charles Pate

As a sommelier and brewer, I have encountered my fair share of beers with bacterial infections. It can be quite disheartening to open a bottle or take a sip of , only to be greeted by unpleasant off-flavors. But fear not, there are ways to detect if a beer has been infected by bacteria or wild .

One of the telltale signs of a bacterial infection in beer is a sour taste. This sourness can range from a subtle tartness to a full-blown puckering acidity. It's important to note that not all sour beers are infected, as some beer styles intentionally incorporate souring bacteria like lactobacillus or pediococcus. However, if you're drinking a beer that shouldn't be sour, then it's likely a sign of an infection.

Another common off-flavor associated with bacterial infections is diacetyl, which imparts a buttery taste and aroma to the beer. Diacetyl is typically produced by certain strains of bacteria, such as Pediococcus damnosus. If you detect a buttery or butterscotch-like flavor in your beer, it's a strong indication of a bacterial infection.

In addition to sourness and diacetyl, there are other off-flavors that can point towards a bacterial infection. One such flavor is reminiscent of soy sauce. This can occur when certain bacteria, like Brettanomyces, produce compounds called phenols that give the beer a soy sauce-like character.

Another off-flavor associated with bacterial infections is a solvent-like or nail polish remover aroma, which is often attributed to the presence of acetobacter. This bacteria can produce acetic acid, giving the beer a sharp, vinegar-like smell and taste. If your beer smells like nail polish or vinegar, it's best to steer clear of drinking it.

It's worth mentioning that not all bacterial infections result in off-flavors that are easily detectable. Some infections may not produce noticeable flavors, but they can still impact the stability and shelf life of the beer. These infections can result in changes in appearance, such as cloudiness or sedimentation, or even cause the beer to gush when opened.

In my personal experience, I once had a batch of homebrewed beer that ended up with a bacterial infection. The beer had a distinct sourness and a slightly funky aroma. It was quite disappointing, as I had put a lot of time and effort into that particular beer. I learned the importance of maintaining proper sanitation practices during the brewing process to avoid such infections.

To summarize, if you come across a beer that tastes sour, buttery, like soy sauce, or exhibits a solvent-like or vinegar aroma, it's likely that the beer has been infected by bacteria or wild yeast. These off-flavors can significantly impact the enjoyment of the beer and are indicative of an infection. It's always a good idea to trust your taste buds and exercise caution when encountering these off-flavors in beer.