Written By: Peter Evans
Date: December 5, 2009 Facts are facts, sometimes batches go bad. What happens when a good beer goes bad? Understanding why those batches went bad (or never were good) will keep you from making the same mistake again and wasting hours on brewing an inferior brew. Being able to properly describe the end product also allows you to discuss it with your fellow brewers on a common ground.

You do not have a metric ton of employees tasting your beer everyday to refine and do quality control on your recipe. Often, it’s just you and a set of friends. For the casual brewer though, quality control is something of the highest order of priority. You want to be able to have a high quality custom beer at an affordable price. So knowing what went wrong makes all the difference.

Generally bad batches are a by-product of the fermentation process or else something that has happened after the process, though not strictly limited to just these two steps.  The most common faults come from improper brewing. This could be from yeast, barley or from hops. Recognizing these through smell will help you zero in on what went wrong.

A Rubber smell will generally be from a fault in the yeast.  A cabbage or “steamed vegetable” smell will also be from yeast. A strong “medicine” smell is most likely from a flaw in the fermentation process. Vinegar smells are from a fault in the bacterial process. The same can be said with a sour milk smell.  An acetone smell is rare for home brewers although as this is usually a by-product of bad corn processing.

Handling your beer is just as important as the care with which you find and prepare the brew. Stirring your beer too vigorously after the boil will result in impurities and air being infused into your final product, which is never good. Light struck beer is often called "skunked beer." This can happen if your batch is exposed for too long to sunlight.  How this comes about when hop oils are converted by light into less than desirable chemicals.  Oxidation is another concern. Again this goes back to your handling of your beer. Usually you can tell by the stale beer smell, even when you think your beer should still be good. This is a common problem but easily reconciled by being careful in how you don’t “slosh” your beer.  Poor head formation is probably one of the biggest issues with home brewing and why a lot of would-be brewers avoid the process all together.  Head formation when a beer is poured is something that can be controlled by a brewer. Fresh beers, such as yours, can form poor heads at first, and that is nothing to worry about as far as taste quality goes.

If your particular brew is normally frothy and has a thick head, but doesn’t all of a sudden, the obvious answer is that the beer has gone stale. Not so obvious is the possibility that your glasses might still have some detergent in them or that temperature of your beer is not what it normally is.

There are literally, thousands of beer troubleshooting guides, but often just posting on a beer forum and waiting for the enthusiastic answers you will get is a good option as well. The voice of experience does go a long way, especially in the centuries old craft of beer making.