How To Tell if Your Homebrew Is Infected (3 Ways)

Homebrewing comes with its own set of challenges, one of which is that the beer can become infected. Infected beer occurs when bacteria or wild yeast get into the homebrew and begin competing with the cultured yeast. Infected homebrew can have a whole range of tastes, from slightly sour or buttery to downright terrible. 

To tell if your homebrew is infected, check whether there is an oily sheen on the top of the beer. As the infection progresses, the beer develops what is known as a “pellicle,” a layer of biofilm. The pellicle can vary widely in appearance depending on what stage of development it’s in. 

You can determine whether or not your homebrew is infected by tasting your beer or observing it over time. If you’re new to homebrewing, keep in mind that many things can look like an infection but are entirely normal during the brewing process. With that said, let’s dive into ways you can tell that your beer is infected. 

1. Look for Signs of Infection in Your Beer

This is the primary way that you’ll determine whether or not your beer is, in fact, infected. You’ll want to pay attention to the coloration of the beer, and what types of foam are forming on top

An infection is often difficult to determine in the beginning stages because it can look similar to the normal processes of making homebrew. 

This is why it’s essential to monitor the possible infection over time. There’s no point in throwing out a delicious batch of homebrew because you think it could be infected.

Most of the time, when homebrew becomes infected, it forms a pellicle, which we discussed a few paragraphs ago. Pellicles are caused by wild yeast such as Brettanomyces or sometimes wild bacteria such as lactobacillus. 

You might be surprised to know that while pellicles may look abhorrent, they don’t make the beer dangerous for consumption. 

Wild yeast and the yeast we typically use to ferment various products aren’t that different. A few thousand years ago, wild yeast was always used to make bread and alcoholic beverages. 

So now that you know a little more about pellicles let’s look at their development process from start to finish. 

The First Signs of a Pellicle

The first thing you’ll notice if your beer has developed an infection is an oily sheen that has suddenly developed on the top of your beer. This sheen can take various forms, but it is usually very thin and has a white tint. 

You may not even notice this at the beginning, especially if your homebrew is still in the beginning stages of fermentation. However, the wild yeast and bacteria multiply very quickly, and it won’t be long before you notice a lot more white showing up. 

As the Infection Progresses

Pellicles are formed in the presence of oxygen, but interestingly, the wild yeast and bacteria forming them do not like oxygen. Instead, the biofilm layer is formed to help protect the yeast from oxygen. 

At this time in the infection, you would expect to see a thicker white layer covering the homebrew. Usually, the layer will have various clumps of bacteria that have bonded together, and webbing spread throughout it. 

The infection may also take on the appearance of noodles at this time, appearing wavy at the top. Typically, if it doesn’t take on this form, it does begin to develop some bubbles around that time. 

These bubbles differ from the carbon dioxide bubbles we discussed a few minutes ago. They will maintain the white coloration. 

The End Stage of a Pellicle

If a pellicle has become well developed, it can take many forms. Most commonly, however, the pellicle will either form a thicker layer of what we’ve already discussed with webbing and clumping, or it can take on another form, which I’m about to discuss. 

A very well-developed pellicle will often be a layer of several large white clumps. These clumps will be grouped on top of one another, with minimal space between them. The formation at this point is reminiscent of Mammatus clouds if you’ve ever observed them in a stormy sky. 

Whether the pellicle has taken on the first form, the second, or something in between, it should be clear at this point that you are dealing with an infection.

However, I still want to discuss some other ways that you can determine whether or not the homebrew is indeed infected. It’s always better to be absolutely sure whenever possible. 

2. Smell the Homebrew

If your homebrew becomes infected often, the smell will be the first sign that alerts you. While I went into visually identifying an infection first, smell plays a huge role in the identification process. 

Standard homebrew beer has an entire range of smells associated with it, but none of them are musty or sour smelling. The fermentation process should have a sweeter aroma to it. Many people have commented that their homebrew smells pleasantly tropical like apples or bananas. 

Your homebrew will also take on various aromas depending on what flavors you’ve added to it. For example, if you’ve added apricot extract to your homebrew, you would expect it to give off the aroma of apricots. 

The fermentation process alone should produce no more than a mild aroma, even with no other flavorings added. While I said it should never smell sour, I think it would be more accurate to say it should never smell intensely sour. A mild sour smell, similar to the smell of sourdough bread, is entirely acceptable. 

What Smells Are Indicative of an Infection?

If your homebrew has become infected, it will typically smell heavily sour or musty. While it likely had a mild yeast smell beforehand, it has a robust yeast aroma at this point. 

If your homebrew equipment hasn’t been through proper sanitation measures and has become infected as a result, you may smell other aromas. 

Some people have reported that their homebrew smells like vomit or even garbage. That’s not normal! If you’d like more information on sanitation measures for your homebrew equipment check out this article

Usually, however, if the infection is only caused by wild yeast or bacteria, it will simply become very sour. The scent will be very pungent, and you’ll likely want to pull away from it quickly. 

The smell, in combination with any visual signs of infection, should have you convinced at this point, but just in case, let’s go over one more way you can assure yourself that the homebrew is infected. 

3. Taste the Homebrew

I know that tasting infected homebrew sounds absolutely disgusting at this point, but keep a couple of different things in mind.

First of all, wild yeast and bacteria aren’t dangerous to your health. In fact, many of these species are actually beneficial to your body system. 

While it may not look very appetizing, it’s certainly not going to bring harm to you. If you’re interested in all the ins and outs of consuming infected beer click here

I do want to note here, however, that if your homebrew has any other smell than intensely sour, I do not recommend doing a taste test. For example, if your homebrew has taken on the aroma of vomit, do not taste it. You probably wouldn’t want to anyways, but just in case! 

Secondly, many beer companies are making and selling sour beer today. Sour beer is exactly what you might think it is. 

It’s a beer that’s been brewed with wild yeast and bacteria. Interestingly enough, sour beer has been gaining popularity over time, so clearly, at least some people like it. If you’re interested, be sure to read up on sour beer here

Sometimes you can even clone these recipes. For more info and some commercial beers you can try making at home be sure to check out this article.

Finally, remember that taste is usually the best way to know whether or not the beer has become infected. This is especially true if there are no visible signs of infection, but you just have a feeling that it’s become that way. 

What Tastes to Look for if Your Homebrew Is Infected

So what flavors should you expect to taste if your homebrew has become infected? Infected homebrew does come with quite a variety of flavors, but usually, it hangs on the sour or buttery side of things. 

If the homebrew has a sour flavor, it may be reminiscent of vinegar. You won’t likely taste a sour flavor similar to citrus in this instance. 

If the beer has a buttery flavor, it’s likely because a different type of wild yeast or bacteria has populated the homebrew. It really is the yeast that causes the flavor of the beer. 

Homebrew Beer – What’s Normal and What’s Not

Beer is a fermented product, and the fermentation process looks slightly different for every batch you produce. 

If you’ve made a few batches already, then you may have become accustomed to the foamy layer that lays on the top of the beer during the fermentation process. This layer is better known as krausen and looks similar to yeast which has begun to ferment for the bread-making process.

New faces to homebrew are sometimes a little bit shocked when the krausen rises higher than they’re used to, but rest assured, all types of krausen are entirely normal for homebrew. 

You may also see small bubbles forming on the top of your homebrew. Don’t jump to conclusions quite yet, though! There’s probably not an infection. While these bubbles, which can look similar to the bubbles that are produced in freshly poured coffee, may look like the beginnings of a pellicle, they’re usually not. 

Instead, these bubbles are often just suspended proteins that have been aerated by the carbon dioxide that resides in your beer. For more information about the brewing process and carbon dioxide click here

If Those Things Are Normal, Then What Isn’t?

If you’re new to this process, it can feel overwhelming to decipher what’s an infection and what’s not. Even if you’re an experienced homebrewer, it can feel confusing if you’ve never dealt with a beer infection. Rest assured, though, infections aren’t that difficult to pick out! 

If you begin to notice a white film lying on the top of your homebrew, it most likely is infected at that point. Pellicles, at their beginning stages, form small white clumps over the beer’s surface. These clumps aren’t usually grouped closer together until the infection has progressed. 

As an infection progresses in the beer, you may notice an entire white film that covers the liquid, usually intermingled with various clumps. The pellicle shares many similarities in appearance with mold, although mold is typically green-tinted, whereas pellicles remain white. 

Another thing to note with infections is that the beer may also develop mold spots. At this point, the homebrew isn’t considered officially infected, but it has something that shouldn’t be there. With mold, getting rid of it is usually as easy as skimming it off the top of the beer.

What You Should Do if Your Homebrew Is Infected

If you’ve determined that your homebrew is infected, two options are available.

The most apparent solution is to throw away the batch of homebrew altogether. To reiterate, under no circumstances should you keep your homebrew if it has the smell or taste of vomit, rotten eggs, or garbage. 

If, however, the homebrew only has a sour smell and taste, it can and probably should be kept. Many people out there prefer sour beer, and who knows, you may become one of them! 

Even if you don’t end up drinking your infected beer, you can always give it away to friends or family who will. 

Final Thoughts

Making homebrew is undoubtedly an adventure; sometimes, it doesn’t turn out quite as we hoped. Luckily, by following the tips and tricks outlined in this article, you’ll be able to make the most out of every batch, regardless of its condition!

About HomeBrewAdvice

Hello, my name is Simon. Together with a group of writers I write about brewing beer and making wine. We all share a passion for the great things in life, such as making stuff from scratch.

The business of HomeBrewAdvice is to bring you great information, stories and product reviews from brewing at home, and making wine


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