Beer School

Diagnosing Problems in Your Finished Beer

updated May 1, 2019
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(Image credit: Melissa Ryan)
(Image credit: Henry Chen)
  • Today’s topic: How to figure out what went wrong with your beer
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Even the most experienced, gifted, and diligent homebrewer still occasionally gets a bum bottle. It happens. And when it does, it’s useful to take a few minutes to try and figure out what went wrong — and how to avoid it next time. Let’s take a look at some of the most common problems with finished beer.

(Image credit: Melissa Ryan)
(Image credit: Melissa Ryan)
(Image credit: Henry Chen)

When something goes wrong with a batch of beer, you know it. It smells foul, it tastes foul, it can even look foul. You won’t make yourself sick if you drink it, so don’t worry if you already took a sip or two, but my guess is that you won’t want to take many more!

It is a major bummer when something goes wrong with a batch of beer — but it’s also a learning experience. Here’s a quick run-down of some of the most common problems that you’ll encounter, along with how to avoid them in the future. (Hint: 99% of them come down to better sanitation!)

Understanding Weird Beer Tastes and Aromas

Butterscotch or popcorn: This flavor comes from diacetyl, which is actually okay in small doses in some beers, like Scottish ales. It usually gets scrubbed away by the yeast during the secondary fermentation, but can sometimes remain if your beer was fermented at an unusually high temperature (above 85°F) or at very low temperatures (below 60°F). It will sometimes go away on its own in a few weeks with beer at room temperature.

→ Next time: Pay attention to fermentation temperature.

Canned corn or cooked vegetables: There’s a bacteria that can sometimes survive in low-alcohol beers that can give the beer this flavor, or in beers that had a slow start to fermentation.

Next time: Make sure your yeast is fresh and active so fermentation gets a good, strong start. If you’re brewing a low-alcohol beer, pay very close attention to sanitation and fermentation temperature.

Cardboard or sherry-like flavors: This is a sign of oxidization — that your beer had too much exposure to oxygen at some point in the process.

Next time: If your beer is nearing its expiration date, this is a pretty normal flavor. If it’s a fresh beer, pay close attention to splashing while transferring and bottling your beer next time.

Funky/barnyard/old leather flavors: A wild yeast strain got in your beer! This can actually be a positive if you like sour beers — if you like the flavor of this beer, go ahead and drink it.

→ Next time: If this funky flavor is not a welcome addition, then be sure to keep all your equipment very clean and thoroughly sanitized.

Granny smith apples/vinegar/tart candy: This is usually a lactobacillus infection. Like wild yeast, this bacteria showing up in your beer isn’t necessary a bad thing. Sour beers are their own kind of awesome, so if you like the flavor, go ahead and drink it!

→ Next time: If you don’t want this flavor showing up unexpectedly, pay close attention to sanitation.

Green unripe apples/unripe fruit: This is often a flavor in very young beers and will go away on its own with time. If this isn’t a young beer or if the flavor is more like Granny smith apples, then you might have a lactobacillus infection (see “Granny Smith Apples” above).

Next time: Let the beer go through secondary fermentation and two weeks in the bottle before tasting it. Pay close attention to sanitation.

Hard alcohol/fusel alcohol/nail polish remover: This often shows up in beers that fermented at above-average temperatures (above 85°F).

Next time: Try to keep your beer somewhere at an average 70°F temperature during fermentation.

Sulfur/rotten eggs: This is another by-product of fermentation that is usually scrubbed away during the secondary fermentation, though it can sometimes be a sign of infection (especially if it’s been several weeks since bottling).

→ Next time: Let the bottles sit for another week or two, and taste them again. If the flavor lingers, then pay better attention to sanitation next time.

Skunky, stale flavor: You’ll get this flavor and aroma if the beer is exposed to sunlight for too long.

→ Next time: Be aware of leaving the fermenting beer or bottles somewhere sunny. Dark-colored glass will help protect the beer, too.

Tannins, or over-steeped black tea: These astringent flavors usually come from accidentally heating the mash over 170°F or pressing on the grains too much during sparging.

→ Next time: Watch the temperature as you mash out before sparging, and don’t press on the grains too much as you sparge.

(Image credit: Melissa Ryan)

Exploding Bottles and Other Physical Problems

Why did my beer gush out of the bottle when I opened it? It might just be that you didn’t let the bottle chill for long enough — chill it for a good eight hours (or overnight) if you can. If your bottles are still gushing but taste okay, then you likely added too much priming sugar when you bottled, either because you measured the amount incorrectly or because your batch was smaller than expected. If it still gushes and tastes funny, then you probably picked up an infection.

→ Next time: Chill bottles for at least eight hours before opening. Measure your amount of priming sugar carefully and adjust the amount as needed if your batch ended up a bit smaller than expected. If it seems like an infection, pay careful attention to sanitation next time.

Why did my bottles explode? If they’re exploding, then either you added too much priming sugar at bottling, you bottled a bit early before fermentation was really finished, or you picked up an infection.

→ Next time: Measure your amount of priming sugar carefully and adjust the amount as needed if your batch ended up a bit smaller. Let the beer ferment for a full three weeks before bottling (high-alcohol beers need to ferment for longer; check your recipe). If it seems like an infection, pay careful attention to sanitation next time.

Why didn’t my beer carbonate? My guess is that either you forgot to add the priming sugar (which happens to homebrewers more often than you might think!), or you waited more than three months before bottling and there wasn’t enough yeast left in the beer to eat the priming sugar you added.

→ Next time: Put the priming sugar somewhere in your direct line of sight so you definitely remember it! If your beer is more than three months old, add another dose of yeast along with the priming sugar when you bottle.

Why is my beer hazy? Homebrew tends to be a bit hazier in general than commercial beers, which have lots of fancy filtering mechanisms. If it bothers you, always pour your beer into a glass and then stop short of pouring the last half-inch or so, which contains most of the yeast sediment that will cloud your beer. If your beer is still hazy, it probably has “chill-haze.” This is an aesthetic problem caused by suspended proteins, but won’t affect the flavor or texture of your beer.

→ Next time: Pour your beer into a glass and avoid pouring the sediment at the bottom. Also be sure to add Irish moss or another clarifying agent in the last 20 minutes of the hop boil.

Why is my beer syrupy, ropey, or snotty? Oh, dear. This is the worst kind of infection, mostly because it’s just so darn gross. Definitely toss the batch.

→ Next time: Pay very close attention to cleaning and sanitation. Be extra sure you’ve cleaned any gunk or old beer residue from reused bottles before using them again.

Brew Better Beer: A Companion to Beer School

(Image credit: Emma Christensen)

I love brewing beer so much, I wrote a book about it! Brew Better Beer (May 2015, Ten Speed Press) is a complementary guide to Beer School. Take a look for even more nerdy details about homebrewing, how to brew 5-gallon batches, and plenty of recipes for different beers.

→ Find it: Brew Better Beer by Emma Christensen

With The Kitchn’s Beer School, we’ll teach you how to brew your own beer at home — and brew it with confidence. In 20 lessons and 7 weekend assignments, we’ll get you set up with your own home brewery, walk you through your first brew day, show you how to bottle your beer, and then toast you on your first pint. Ready to brew your first beer? Join us!