We’ve told you to never give up on brewing, but that doesn’t mean that every bad batch can be salvaged. The tough part is that, until you’ve experienced it yourself, you won’t know whether or not your beer is beyond hope. Some problems can be easily addressed if the beer is still in the fermentor. Other issues may improve with time. But there’s a definite list of things that won’t get better. Even if your beer is in that latter category—or if time doesn’t help—you might have some options, depending on how bad it is. There’s a big difference between missing your target and ending up with an undrinkable beer. In either case, you should troubleshoot the cause, but for now let’s figure out what you can do.
The Good
When your yeast doesn’t do its job, you can end up with a stuck fermentation, which leaves you with five gallons of sweet, under-attenuated beer. Maybe you didn’t start with enough yeast or the environment was too harsh. Typically, you’ll notice this before you package your beer (you do check your final gravity, right?), which means you still have time to resurrect this batch. There are few things to try. First, warm it up 5–8°F (3–4°C) and see if that helps. If not, you can repitch with a strong starter at high krausen or a couple of packets of dry yeast. Failing that, you could rack it onto the yeast cake from another batch.
In some situations, you can end up with a significantly under-hopped beer, often caused by poor recipe formulation or by missing a hops addition. In this case, you can dry hop to pick up aroma and blend in a hops tea to get bitterness and hops flavor.
Diacetyl, which produces a buttery or butterscotch flavor, can fall into this group if you catch it before bottling or kegging. Yeast activity will usually drive this off, so warming up the fermentor a little may rouse the yeast enough to clear it out.
The Bad
In some cases, time can heal a bad batch. Beers that are over hopped, under carbonated, or overly estery will often improve if left alone. Give it a month and then try another bottle to see where you are. Harsh alcohol character, such as solvent-like aromas and hot mouthfeel can also get somewhat better with age. Finally, acetaldehyde flavors (green apple and/or cidery notes) will also pass with time.
Unless you really need to clear out the batch to free up the bottles, keg, or the fermentor for a new batch, try being patient. Another month or so could make a world of difference.
The Ugly
Unfortunately, the “Ugly” category is fairly extensive. Phenols and chlorophenols, sourness, oxidation, DMS (cooked corn or cooked cabbage), light-struck skunkiness, diacetyl in the bottle, astringency, and mold—none of these will get any better over time. Over-oaking, which can contribute to astringency, is also permanent. If none of the options below seem workable, then it’s time to throw in the towel on this batch and prepare for the worst case: dumping it or composting it.
Strategic Options
Before you decide what to do with the batch, consider where the beer falls on the scale between “too heinous to ingest” and “meh.” Even if it’s not to your taste, you could share it with some friends whose palates are less discerning. Heck, after a few good beers your own sense of taste might be impaired, which means it could serve as a good nightcap beer.
Depending on the off-flavor, blending might also be a reasonable choice, but you need to be careful not to throw in good beer after bad. Over-oaked and super hoppy beers are good candidates for blending, as are beers with interesting character that just need to be toned down.
Brewing mistakes can also be used in the kitchen by converting the beer to malt vinegar, or by cooking with it. Cooking is much more forgiving than drinking it directly. There are plenty of recipes out there that use beer in marinades and sauces, add it to broths, chili, and stews, or even use it in breads and cakes. Let your senses be your guide here. If the batch is really foul, especially with chlorophenols, don’t risk ruining your meal.
Finally, if all else fails, let it go. Dump it out without hesitation. It may not be drinkable, but it can still serve as fertilizer for your yard or compost.
Regardless of how things play out, spend some time on a post-mortem to figure out what went wrong, then put it behind you.