Fermentation is such a strange and marvellous thing - the magical process undertaken by yeast to transform our carefully curated wort into beer. This process can lead to some interesting sights and smells being created though which often leads brewers to wonder, "is this beer infected"? Here are a few signs (and false alarms) to help determine if what you're seeing/smelling is normal, or if you are in fact dealing with some kind of infection in your beer.
Look At It
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;
- If you're seeing lots of small bubbles on the surface, this is normal and a sign of fermentation being underway, or beginning to ramp up (ie. not an infection).
- If you see a consistent bubbly, foam like substance on the surface, this is krausen and is definitely normal (ie. not an infection).
- If you're seeing chunks of matter clumped together and floating on the surface, this is likely "yeast rafts" and is normal (ie. not an infection).
- If you're seeing large chunks of matter floating around within the wort and not the surface, this is likely cold break, and is simply proteins within the beer clumping together and is normal (ie. not an infection).
- If you're seeing larger bubbles on the surface, potentially with 'stringy bits' joining them together, this is likely a pellicle and is a good sign of an infection.
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| An example of a krausen sitting on top of fermenting beer |
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.
Smell It
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.
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 for the smell of infected beer are "sour", "skunky" or "musty", or even like vomit.
Taste It
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.
You'll know fairly quickly from tasting whether or not you're dealing with an infection. 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 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.
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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