Homebrew School: How To Tell If My Beer Is Infected?

Introduction

Fermentation is a fascinating and magical process where yeast transforms your carefully curated wort into beer. This process can lead to some interesting sights and smells, often causing brewers to wonder, "Is this beer infected?"

In this guide, we'll explore the signs (and false alarms) to help you determine if what you're seeing or smelling is normal, or if you might be dealing with an infection in your beer.

Visual Signs of Infection

A pellicle will generally form on the surface of your fermenting beer when it has some kind of bacterial infection. It can sometimes be difficult to distinguish between what is a pellicle, and what is normal - krausen, bubbles, or yeast rafts are often sitting on top of your fermenting beer and can be mistaken for signs of infection.

It can be difficult to specify in general terms exactly what to look for, but here are some guidelines;

• Small Bubbles: Lots of small bubbles on the surface are normal and indicate fermentation being underway (ie. not an infection).

• Krausen: A consistent bubbly, foam-like substance on the surface is krausen and is definitely normal (ie. not an infection).

An example of a krausen sitting on top of fermenting beer

• Yeast Rafts: Small chunks of matter clumped together and floating on the surface, this is likely yeast rafts and is normal (ie. not an infection).

• Cold Break: Large chunks of matter floating within the wort and not on the surface is typically cold break, which is simply proteins within the beer clumping together and is normal (ie. not an infection).

• Pellicle: Larger bubbles on the surface, potentially with 'stringy bits' joining them together is likely a pellicle and is a tell-tale sign of an infection.

A Google image search for the terms "pellicle", "krausen", "yeast rafts" or "beer infection" will help give some indication on what to look for. It's definitely worth researching other peoples posts and photos on homebrewing forums and Facebook groups, as chances are someone has already asked the question with a beer that looks exactly like yours does right now.

Aromatic Signs of Infection

If you're still not sure from the visual signs outlined above, the next step would be to open your fermenter and have a smell of what is inside. If it smells like beer, or hops, or some kind of combination of both, you're good.

• Sulphur or Rotten Egg Smell: If you're getting a sulphur or rotten egg type of smell, that is a warning that something might be wrong here, but keep in mind this particular type of smell can be generated by some yeast strains (such as lager yeast) so may well be normal.

• Descriptors of Infected Beer: Infected beer often smells "sour", "skunky" or "musty", or even like vomit.

Flavour Indicators of Infection

The last step if from looking and smelling you are still not sure or convinced whether or not you're dealing with an infection is to have a taste. Rest assured, even if you take a sip of infected beer, it's not going to harm you or make you sick, so give it a try.

• Infected Beer Taste: It will taste acidic, rancid or rotten. If you'd describe it in any way other way, then there's a good chance it's fermenting away just fine and as expected. Fermenting beer will perhaps have some funny or strange flavours but it won't taste foul. For example, if you're noticing a "buttery" type of taste (or smell), this is often caused by diacetyl which is produced (and then cleaned up/removed) by yeast as part of the fermentation process.

What to Do Next?

Even if you think you have an infected beer, it can sometimes be worthwhile letting it ride out to see how it turns out after a couple of weeks. Bacterial infections will likely lead to a sour beer, but these styles of beers can sometimes turn out pretty good. Don't be too quick to dump a beer until you've given it a chance to fully ferment and see how it turns out.

If you're unsure, then chances are your beer is fine and you should definitely wait it out. You can also try posting a photo of the current state in a homebrewing forum or Facebook group to gauge the opinion of others.

Conclusion

Remember, sanitation is key when it comes to brewing. If you've been diligent with cleaning and sanitising your brewing equipment then your chances of ever dealing with an infection are very low.

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