Guide to Dealing With Infected Beer

The fermentation process although exciting at times can at the same time be concerning for the novice brewer. Each fermentation can behave and look different from the last, as a result, one of the biggest concerns shared by many is whether or not they are dealing with a beer infection.

Many a person starting out in this hobby, ourselves included, has asked, “is my beer infected”?. Although strange reactions can occur during fermentation the good news is that infections are relatively rare occurrences, so before becoming overly concerned and making the decision to pour your beer down the drain it is important to be able to differentiate between what a healthy fermentation looks like versus an infected one.

Is My Beer Infected?

The best way to be able to determine if a beer is infected is to know what a healthy fermentation looks like. As the yeast goes to work converting the sugar in the wort over to alcohol and CO2 it causes a noticeable reaction. Once active fermentation begins, over the next 2-3 days you are going to notice a lot of activity happening within the fermenter or carboy.

There will be little pieces of proteins moving around vigorously within the wort, a build-up of sediment or what is referred to as trub will be seen at the bottom of the fermenter and most noticeable of all will be the formation of thick foamy bubbles at the top of the wort, this formation is referred to as krausen and is perfectly normal. However, this formation is what causes many people new to brewing to become concerned about an infection.

If you are concerned that an infection may have occurred there are five things to look for to help you make that determination:

  • How the beer looks
  • How it smells
  • How it tastes
  • What is the final gravity
  • Beer gushers

Examples of Infected Beer

The following are examples of what to look for in an infected beer.

The Formation of Pellicle

Doing a visual inspection may show the presence of Pellicle. Pellicles appear as microbes at the top of the wort. They look significantly different than krausen and once you know the difference it is easy to distinguish between the two. 

photo of a beer infection called pellicle
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Although different infections can cause Pellicles to vary in appearance from each other in general they do appear similar and are quite easily detected. They can be described as looking like an oil slick or film containing white bubbles with what looks like spider webs coming off them.

This type of infection is a result of the beer being exposed to wild yeasts or bacteria such as Brettanomyces or Lactobacillus often referred to as LAB. These unwanted guests prefer to do their work in an oxygen-free environment referred to as anaerobically and as such create this protective barrier that you are seeing as a means to block oxygen from penetrating the wort.

The Presence of Mold

The growth of mold in beer although very rare can occur. It is very easy to spot a fuzzy green, white or brown growth on the top of the beer. It typically takes a very long time before a beer will become moldy and usually only happens if you have left your beer in the fermenter for too long. It is recommended that you do not allow your beer to stay in the fermenter for any longer than 3 – 4 weeks.

Strange Odor

Fermentation can create some strong odors and most odors do not mean that there is a beer infection. However, if you are getting an overly strong egg smell (sulfur) or a vinegar-like smell then there is a chance that it is infected and it is worth exploring further.

The Beer Tastes Bad

Beer goes through many different stages as it ferments, conditions, and then carbonates and during these stages, it will develop different flavors and some of them undesirable. If you are sampling the beer at different intervals and an undesirable flavor is present it is important to understand that it may just be part of the process and not necessarily an indication of an infection.

As the beer ages and matures, many of these off flavors will melo out; however certain flavors are an indication that the beer has become infected. If the beer has flavors that taste like vinegar, or butter, or is sour tasting then you most likely have an infected beer.


If you find that your beers are continuously over-attenuating then you may have an infection. Over attenuation is when your final gravity reading is much lower than what your target was. This happens when a wild yeast continues to ferment your beer after the yeast you added has finished.

Bottle Gushers

Bottle gushers occur when bacteria is present in the beer when you bottle it. This bacteria will continue to work away on the beer in the bottle creating an excessive amount of carbon dioxide. This access amount will then over pressurize the bottle and when you open it the beer sprays all over the place, resembling a gusher of sorts.

What To Do With Infected Beer 
a picture of an infected beer in a fermenter.
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The hardest part of discovering a beer infection is deciding what to do with the beer. Most people will simply pour it down the drain and there is a good chance you may have to do that.

However before wasting all of that beer have a taste of it, if it tastes really bad then you most likely do need to dump it as the taste in most cases will not improve. But if no significant off flavors are detected then consider putting the lid or airlock back on and letting the wild yeast finish.

Sour beers are brewed using wild yeast strains like Brettanomyces and Lactobacillus and even though you did not intentionally pitch those yeast strains they may be what is infecting your beer and you could end up with a good-tasting sour beer. The thing to note is that it could take many more weeks or even months for this beer to finish.

There is a caveat with doing this, however, once your beer is infected with these yeast strains so is your equipment, and although possible it is very difficult to get rid of them resulting in future batches of beer brewed using the same equipment running the risk of also becoming infected.

As a result, you are going to need to replace the equipment on the cold side. The hot side is fine as the boiling stage sanitizes the beer. Keep the infected cold side equipment and use it to brew sour beers moving forward.

How to Prevent Your Beer From Getting Infected

The main reason for a beer infection is poor cleaning and sanitizing procedures. It is important to thoroughly clean and sanitize any piece of equipment that is going to come into contact with your beer, especially on the cold side equipment. The cold side is everything that happens after you turn your kettle off.

If you have an infection you will either need to throw out the cold side equipment, use it for making only sour beers or you can attempt to clean and disinfect it by soaking it in a bleach solution and giving it a heavy rinse. If your next batch becomes infected you will know your attempt at getting rid of the infection has failed and decide what to do with the equipment at that time.

It is also important to pay close attention to preventing your wort or beer from being exposed to oxygen as much as possible. Exposure to oxygen is typically the reason for an infected beer. Pay close attention when transferring your beer between containers, don’t let it splash around. Do not give into the temptation to open your fermenter lid to look at the beer, keep the lid on, and if using an airlock keep it filled with sanitizer at all times.

The Final Word

Dealing with an infected beer although a discouraging aspect of brewing is a reality that all brewers will have to deal with eventually. Understanding how to determine if your beer is infected is the first step to addressing the problem. Although prevention is the best course of action; when an infection is detected realize it is not the end of the world and there are options available to you such as brewing sour beers.

P.S. Be sure to grab your gift on the way out. On the side of the blog or at the bottom if on your smart device pick up Robb’s top 5 best-selling recipes from his brewpub. Cheers!

2 thoughts on “Guide to Dealing With Infected Beer”

  1. Very informative articles you are writing!
    Much appreciated,


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