Is your beer infected?

Infection is a term use to describe an unintended flavor created by wild yeasts or bacteria. Usually brewers find that sanitation practices are to blame for an infection. So you’ve made a batch of beer, maybe it’s your first or maybe it’s your tenth, but this fermentation is looking a little… weird. You looked inside and oh no… what’s that growing on top, krausen, mold, or something else?! You wonder what to do now. You spent 50 bucks on this batch and now your thinking you’ll have to dump it down the

So is your beer infected?

The short answer: Maybe, but probably not. In the wise words of Charlie Papazian:

Relax. Don’t worry. Have a homebrew.
(Or store bought beer if this is your first time)

Why you shouldn't dump the batch

Here’s the deal, your batch could be infected but don’t dump it so hastily. You’ve invested a lot of time and effort into your beer so consider a few of your options first.

Your batch may not be infected

thumb2_krausen-60470Your batch may not have an infection at all. It’s very common for brewers, new and old, to misdiagnose their beer. More often than not the beer is perfectly fine. Not all fermentations are alike, and different strains of yeast can behave differently.

Plus, let's face it, krausen looks crazy sometimes.

The batch may not be "bad"

Taste your beer. If you don’t clearly see Mold, or a pellicle than use a sanitized measuring cup or wine thief to draw out a sample. This is by far the best way to determine if you’ve got a bad batch. From my personal experience if you have an infected beer, you’ll know. Depending on what little bugs have taken over in your fermenter you might note things like: Butter, Vinegar, tart cherry, wet blanket and barnyard. Basically if you taste your beer and it tastes awful than you may want to toss it, but not before. There are stories of beer tasting completely different from what the brewer intended but still very good despite an infection.

Always remember, don’t put any beer back into the fermenter after you take it out. You don’t want to contaminate your beer if it was actually infection free.

How do you tell if it's infected?


Now if you do see what looks like white or green fuzzy mold than you can attempt to siphon your beer from below the mold and leave an inch or  two in the fermenter with the mold still undisturbed and floating on top. I’ve read of success with this method so I would try it to save your batch of beer. It might sound gross but hey, there’s 5 gallons of beer under there!


A pellicle is a good sign of infected beerIf the top of your beer looks like it has a layer of white chalky film and bubbles that don’t pop then you definitely have an infection.  A lot of brewers suggest dumping a batch of beer with this type of infection. But your other option is to let the beer age longer to see if you get a tasty sour out of it.

Bottling any beer with an apparent infection can be risky (read dangerous). Wild yeast and bacteria will consume much of the residual sugars that your brewing yeast left behind. Partner that with the sugar you add at bottling and you have the potential for bottle bombs, and gushers. Believe me they aren’t as fun as they sound.

Brewing beer can be complicated, or even overwhelming when you are beginning. So if you can focus on one thing while brewing, make it sanitation. Ignoring thorough sanitation can lead to some big time disappointment. In fact, I’ve seen plenty of new brewers stop after their first batch because it didn’t turn out, which is very sad to see.

Here is a little personal wisdom I’ve gleaned from my many years of brewing; If, while brewing, you ever think to yourself “did I sanitize this” take an extra second to sanitize again. Over time your sanitation techniques will become second nature, and your beer will improve greatly because of it.

by John Rogers


Papazian, C. The complete joy of home brewing (Rev. ed.). New York, NY: HarperCollins, 2003. Print.


written by John Rogers

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