How to Tell if Your Beer or Mead is Infected

The fermentation process can look alien at times, which may make you ask yourself "is this infected?" Once you've asked yourself that question, you begin to go down the rabbit hole and start to contemplate dumping your homebrew down the drain. But before you take that step, you should be very sure that it's a dumper. This article will help you decide if your batch is infected, and if so, if it's worth dumping or pressing on. From day one of learning to brew your own beer, mead, or wine, cleanliness and sanitation has been (hopefully) drilled into your mind. That's because the wort or must we make is an almost perfect environment for microbial growth. Let's look at a few examples what classifies as an infected batch, and just a regular healthy one. After that we'll cover what to do if you do indeed have an infected batch.

Is This Infected?

Answer: No What is This?: This is called krausen. It is a foamy layer of yeast, hop particles, trub, CO2, and any other proteins that found a way into your beer. They are in fact, completely normal and happen with almost every batch you beer you make. There are always a few exceptions where one doesn't form or only a small one forms, but for the most part they are just a part of the process. Once primary fermentation begins to wrap up, the krausen will drop out as well. It's okay if your beer doesn't produce a krausen as long as the gravity is dropping. A krausen can look slick with small bubbles or very airy with large bubbles. They can be any color from tan to green and brown.

Is This Infected?

Answer: Yes What is This?: This is the beginnings of a pellicle forming on the surface of your homebrew. It is officially infected. A pellicle is created by brettanomyces and various lactic acid bacteria (lactobacillus and pediococcus or LAB for short) as an oxygen barrier. Brettanomyces and LAB prefer to work anaerobically, which means without oxygen. In an infected beer, a pellicle only represents the presence of oxygen, and does not represent the severity of the infection, or the status of its fermentation. They will come and go as the beer becomes exposed to oxygen (removing the airlock or lid are common culprits of oxygen exposure). In fact, some intentionally sour beers will never even form a pellicle.

Is This Infected?

Answer: No What is This?: This type of photo is more commonly inquired about with mead-makers but does still apply to all types of fermentation. This lightly colored build up on the bottom of your carboy is called lees, yeast sediment, or trub, depending on what you're making and who you ask. The bottom line is that it is a by-product of a fermentation and is harmless to your batch. Sometimes it will streak down the sides of your fermenter, or leave a ring around the top. Both of those situations are also normal and don't represent an infection. On the bottom, the sediment can be light and fluffy or appear dense and compact. When you transfer to a secondary (mead and wine-making only), leave the lees behind. For beer, leave it behind when you transfer to a keg or bottling bucket.

Is This Infected?

Answer: No What is This?: This is also not an infection. It may look like some small bubbles forming in a pellicle, but it is just a few suspended proteins inflated by CO2 that is in your beer. You'll usually find this occurring after a couple weeks of fermentation and you go to bottle or keg your beer. If you washed your fermenter with soap and weren't diligent in rinsing, there may also be a slight sheen on the surface as well. This is just a bit of oil that is floating on the top. While not the ideal for head rentention, it's harmless.

Is This Infected?

Answer: Yes What is This?: This is a well developed pellicle. As you read before, there was a significant amount of oxygen exposure, and the LAB is working hard to keep it out of your beer. Pellicles can take up all shapes and sizes. This one in particular looks like ramen noodles, while others look completely different. Regardless of its visual formation, its purpose is still the same (block oxygen from entering).

Is This Infected?

Answer: Yes What is This?: This is yet another well developed pellicle. It's very different from the one above it, but it's still shows that some kind of brettanomyces or LAB is present with oxygen.

I've Determined My Beer is Infected: Now What Do I Do?

Your first instinct may be to dump it, toss any cold side (post-boil) equipment that touched it, and count your losses. However, there's a better and more logical way to approach the situation. You may or may not have had some commercial sour beers, but they can in fact be pretty tasty. Even if you didn't pitch brettanomyces, "wild" yeast or LAB on purpose, you still may end up with a good final product. So the first thing you should do is try it. If it tastes like hot garbage, it won't hurt you, but you should know that it's not likely to improve, and it's time to dump. However if no unpleasant  flavors are perceived, you should consider putting the stopper or lid back on and letting it finish out. This could take a several months or even longer, but that's okay. The thing to remember here is this; If you were just going to toss your infected equipment, you still need to buy replacement equipment regardless. So why not start making sours by keeping your infected equipment for sour making and clean equipment for clean beers. Many brewers who make sours start this way, then add on to their equipment for souring as they replace old fermenters and siphon hoses.

Hidden Infections

The last thing to mention is a hidden infection. You may have come here with a strange visual hint and wanted some answers, but an infection may be present without you even knowing it. If you have a persistent off-flavor that continues to appear with every batch you make, you either have an infection or need to clean / replace your siphon lines. Another more obvious sign of a hidden infection is a continuous over-attenuation. For example let's say you use a pack of S-04 which attenuates to around 70%, but every time you make any beer, you get an attenuation of at least 80% every time regardless of the yeast selection. This means that a wild yeast is continuing to ferment your batches to its attenuation if another yeast stops first. This also likely means it's well established in your siphoning and bottling equipment, so make sure to replace them.

Preventing Future Infections and Off Flavors

In the event of an infected beer, the best thing to do is locate all of the potential infected equipment and replace it. Catching one early is crucial if you have multiple fermenters, because if a racking cane is infected it can spread the infection to all the fermenters you've transferred  from. Infected equipment should be replaced or dedicated to sour only brewing. Hydrometers, and racking equipment are usually the highest risk vectors for transmitting brettanomyces and LAB, so those should be replaced first.  Technically a bleach solution soak could be used to kill the infection, but results aren't guaranteed, especially in plastic. Heavy rinsing will also be required. Hot side equipment is at little to no risk of transferring an infection. This is because the wort is boiled for a considerable amount of time, so even an infected mash-tun (usually LAB from sugar and grain remnants due to poor cleaning) won't carry over to your fermenter because of the boiling stage. Off flavors from a dirty mash-tun are another story though, so keep it clean. Remember that the best way to prevent an infection in your beer is to have clean and sanitary equipment through the entire brewing process, so be sure to stock up on Sanitizer and Cleanser.

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