Is My Homebrew Beer Infected? How to Save a Bad Brew

Learn how to tell if your brew is infected or if your brew is good, the causes of infection, and steps to prevent and salvage an infected batch.


Mat Stuckey

9/2/20234 min read

An infected batch of homebrew beer
An infected batch of homebrew beer

How to Tell if Your Homebrew Beer is Infected

Is your homebrew beer infected? It's a common question many home brewers ask. An infected batch of beer can be a homebrewer's worst nightmare. It’s important to be able to tell if your homebrew is infected so you can prevent it from happening in the future and salvage your brew if possible.

This article will guide you through the signs of an infected beer, the causes of infection, and what to do if your brew is infected.

What is an Infected Beer?

An infected beer is one that has been contaminated by bacteria or wild yeast that are not part of the intended yeast strain used for fermentation. The unwanted microorganisms can produce off-flavours, sourness, and sometimes even make the beer undrinkable. Common culprits include wild yeast such as brettanomyces, and bacteria like lactobacillus and pediococcus.

What Causes Beer Infection?

The main cause of beer infection is poor sanitation. Any equipment that comes in contact with the wort or beer post-boil needs to be thoroughly cleaned and sanitised. Even a small amount of bacteria or wild yeast can multiply quickly and infect your beer. Additionally, exposure to oxygen post-fermentation can also lead to infections as many spoilage organisms are aerobic.

How Does Fermentation Look in Healthy vs Infected Beer?

Healthy fermentation typically starts within 24-72 hours after pitching the yeast. A layer of krausen, which is a thick, foamy head, will form on top of the wort.

This is composed of yeast, proteins, and hop residues and is a good sign that fermentation is proceeding well. As fermentation progresses, the krausen will start to subside, and sediment will build up on the bottom of the fermenter.

In contrast, an infected beer may have a pellicle forming on top. A pellicle is a thin layer of biofilm formed by bacteria or wild yeast in the presence of oxygen. It can appear shiny and oily, or thick and leathery, sometimes with small bubbles forming underneath.

Signs Your Beer is Infected: How to Tell if Your Brew is Bad

  • Off-Flavours: If your beer tastes sour, buttery, or has any other off-flavours, it might be infected. Off-flavours can be caused by wild yeast or bacteria.

  • Unusual Appearance: A pellicle on the surface, unusual sediment, or strange colours can be a sign of infection.

  • Foul Smell: If your beer smells like rotten eggs, vinegar, or any other unusual odours, it might be infected.

What to Do if Your Homebrew is Infected?

First, don’t panic. Not all infections will ruin your beer. Some may even add complexity and make it taste better, like in the case of sour beers intentionally fermented with wild yeast and bacteria.

However, if the beer tastes or smells really bad, it’s probably best to dump it. If the infection is mild, you may be able to salvage the beer by pasteurising it, adding more yeast, and letting it ferment out.

Preventing Infection in Your Beer

  • Proper Sanitation: Make sure all your equipment is thoroughly cleaned and sanitised.

  • Limit Oxygen Exposure: Avoid exposing your beer to oxygen after fermentation has started. Use an airlock to allow CO2 to escape without letting air in.

  • Healthy Yeast: Make sure to pitch a healthy and sufficient amount of yeast.

Cleaning and Sanitising Procedures (Important!)

Cleaning and sanitising are two crucial steps in the brewing process. Cleaning involves removing all the visible dirt and residues from your equipment. Sanitising involves killing all the microorganisms on the surface of your equipment.

It’s important to clean thoroughly before sanitising as sanitisers are not effective on dirty surfaces.

We recommend VWP steriliser, one tub makes 120 gallons and it works perfectly. A small price to pay for peace of mind. You can buy it on Amazon using the button.

Can You Drink an Infected Beer?

It depends on the severity of the infection. If the beer has a slight sourness or funkiness but is otherwise palatable, it is safe to drink. However, if the beer has strong off-flavours or smells really bad, it’s best to dump it.

How to Salvage an Infected Batch?

If the infection is mild and the beer is still drinkable, you can try to salvage it by doing the following:

  • Pasteurise the Beer: Heat the beer to 140-160°F (60-71°C) for a few minutes to kill off any remaining bacteria or wild yeast.

  • Re-pitch Yeast: Add a fresh, healthy yeast culture to help ferment any remaining sugars and outcompete any surviving spoilage organisms.

"So, Is My Beer Infected?" Maybe Not.

Key Takeaways

  • Infections are caused by bacteria or wild yeast contaminating the beer.

  • Proper sanitation and limiting oxygen exposure are key to preventing infections.

  • Signs of infection include off-flavours, unusual appearance, and foul smell.

  • Some infections can be salvaged, but severely infected beer is best dumped.

  • Cleaning and sanitising your equipment properly is crucial for making good beer.

It is essential for any brewer, whether a novice or experienced, to understand the signs of an infected beer and how to prevent it. A bad batch of beer can occur for several reasons, from unsanitary conditions to unwanted yeast or bacteria getting into the brew.

It is crucial to understand the appearance of fermentation, like krausen and pellicle, to differentiate between a normal fermentation process and an infected one.

Ensure that everything that comes in contact with your brew after boiling is thoroughly cleaned and sanitised. This includes the fermenter, airlock, and any other tools used in the brewing process.

Remember that an infection may occur from wild yeast or bacteria, such as lactobacillus and brettanomyces. It's also important to remember that the presence of a pellicle does not necessarily mean your beer is ruined. While a pellicle indicates the presence of oxygen and wild yeast or bacteria, some sour beers intentionally have pellicles and turn out delicious.

While the fermentation looks can be a telltale sign, the ultimate test is the taste. Off-flavours, caused by wild yeast or bacteria, can indicate an infection. However, some off-flavours can also occur naturally and may dissipate over time.

If you are new to brewing, you may get quite often confused, so always seek advice from more experienced brewers or online communities.

Lastly, if you have confirmed that your batch is infected, and it tastes off, it is better to dump it and start anew with a more sanitary approach. It's a hard decision, but it's better than risking your health or sharing bad beer.

However, if the infection has not ruined the taste and you are making a sour beer, it may still be salvageable. Always remember that proper cleaning and sanitising procedures are crucial to preventing infection in your beer. Good luck!

Want more homebrewing information and tips? Head over to the Brewpedia blog for more!