Infected, spoiled, sour beer is every brewer's nightmare. Pouring out bad beer is one of the most unpleasant experiences in the brewing hobby. Fortunately, while maintaining the rules of cleanliness and disinfection in a home brewery, beer infection does not happen often. To protect yourself from an enemy, you need to know him. Proper identification of the symptoms we observe on beer is crucial to save ourselves stress. Often, even non-novice brewers confuse infection with completely harmless symptoms of fermentation. So let's take a look at the most common infections that our homemade beer can encounter.


The most characteristic symptom of beer contamination at the fermentation stage is a film evenly drawn over the surface of the young beer in the fermenter. Often referred to as pellicle

 

 

The membrane can take various forms and is sometimes confused by novice brewers with the final stage of the foam blanket. It differs from it in that it does not have clusters of fine CO2 bubbles that are characteristic of fermentation foam.

 

The symptoms of infection are often clusters of fine yeast flakes that float on the surface of the beer or settle on the edges of the fermenter. Remember that the infectious pellicle is always white or of similar shades. The yeast flakes are beige to brown in color. Pellicle particularly at the beginning, has a homogeneous, membrane-like surface that thickens very quickly. Over time, it may take the form of a very fine spider's web or bubbles may appear on its surface. However, they are definitely larger than the bubbles that make up the fermentation foam.

 

The membrane that appears during infection is the accumulated clusters of microorganisms that have started to develop in our beer. Removing the membrane, unfortunately, will not get rid of the infection. All beer is infected. Fortunately, it is not always the case that beer with a proven pellicle is only suitable for tapping. In the initial stage, the contamination of the beer does not have to be felt, and since the microorganisms that can develop in the beer are not harmful to health, there is nothing to prevent bottling such beer. It should be noted, however, that it will be a beer for quick consumption, before the infection also begins to appear in the taste. Bottling of beer and refermentation will cut the oxygen and fill the bottle with CO2 over time, which will effectively inhibit the growth of microorganisms that require its presence - i.e. aerobes. Of course, some microorganisms that infect beer do not require the presence of oxygen, but a large group of them will not survive without it. Remember that such bottled beer should also be controlled in terms of carbonation, some of the microorganisms can ferment residual sugars in the beer, causing them to carbonate, which may result in tearing the bottles after prolonged aging. The most common taste of infection in beer will be its sourness, which is caused by the majority of aerobes. They are usually also accompanied by the presence of pellicle.

Infections with wild yeast strains are much more burdensome. They are not always accompanied by the presence of biofilm, and they almost always permanently change the taste of beer. It may happen that we will be lucky and find a wild yeast strain that will bring noble fruity notes, slightly sour typical of lambik. Unfortunately, however, the most common and least pleasant symptom of wild yeast infection is the characteristic smell and taste of chlorophenol. Described as the aroma of a pharmacy, hospital, lysol, dentist. It is so clear and intense that it is impossible to confuse it with anything else. Unfortunately, such beers are only suitable for tipping. Even the toughest guys quit after drinking a few sips.

Another type of infection that can appear in homemade beer is the growth of mold on the surface of the fermented beer. While in this situation it does not have to change the taste, the beer should be poured out because of the toxins released by the mold.

The identification of mold in beer should not pose any problems, it resembles bushy white-green blooms that can be observed on many food products.

How to prevent beer infection?


The cleanliness and disinfection of equipment protect us against beer contamination. Remember that the most vulnerable to infection is the cooled down wort before fermentation or at its initial stage. Young beer, which has already fermented, is less susceptible to it, due to the alcohol that protects it, the lowered pH unfavorable to the development of many microorganisms, a very strong biological monoculture in the form of brewer's yeast cells, which prevent the development of other bacterial cultures. Therefore, let's take care of thorough washing and disinfection of fermentors and other equipment that comes into contact with the wort after cooking. Fermenters should be washed and disinfected not only before but also after fermentation. The emptied fermentation container should be immediately washed and disinfected. so that organisms (e.g. wild yeast) do not develop in it, which can penetrate deep into the walls of the fermenter and it will be difficult to get rid of them later. The most popular agents for current disinfection are Oxi, sodium metabisulfite and Starsan.

 

The fermentor, in which we already had contaminated beer, is either very thoroughly disinfected with a strong agent, e.g. soda lye, or we simply replace it with a new one. Replacement in the case of plastic fermentors is not associated with a high cost, and gives us much more confidence that we will not repeat the infection of the beer.

Another safeguard is to ensure the best possible working conditions for brewer's yeast. Quick start and efficient fermentation protect our beer against the development of undesirable microorganisms in it. Alcohol and a huge amount of yeast cells will appear in healthy fermenting beer, creating a natural protective barrier. The basic conditions for efficient fermentation are the right amount of healthy and strong yeast, oxygenation of the wort before fermentation, appropriate fermentation temperature, wort rich in nutrients for yeast. The latter condition is usually fulfilled by a ready-made beer wort, rich in nutritional microelements, but in the case of strong beers, it is worth supplementing it with yeast conditioner.


Beer infection is undoubtedly the terror of brewers. Usually, sooner or later it will happen to anyone brewing beer. However, one should not be overly afraid of it. By following the guidelines presented, we will effectively reduce the likelihood of its occurrence. And the beer in which it has already appeared does not always have to be only intended for pouring out.