As you learn to brew craft beer, it is important to familiarize yourself with potential off-flavors. In an ideal world, every batch you make would be perfect. However, chances are that you will eventually make a mistake. We have all had a bad batch of beer at some point. It happens. Of course, there is a difference between a beer that is disappointing and one that is offensive. Usually, you will know right away if your beer is off. Trust your taste buds and instincts. However, sometimes it helps to confirm your suspicions. Let’s explore the possible off-flavors you may encounter.
1. Alcoholic
There is such a thing as an alcoholic off-flavor. Obviously, we need alcohol in our beer, especially in stronger varieties like imperial stouts and barleywine. But beers that are intended to have moderate alcohol levels can taste too boozy if the fermentation process goes wrong. To understand the problem, we need to know what kind of alcohol we want and those we don’t. The alcohol we want in our beer is ethanol, which yeast produces when converting the sugars in our wort. However, sometimes other alcohols want to join the action, primarily:
- Propanol
- Isobutanol
- Butanol
- Isoamyl alcohol
These are known as fusel alcohols. In truth, you will find traces of these alcohols in almost every brew. Most of the time, their quantities are so small that we don’t notice them. However, our taste buds are sensitive, and even a tiny amount can ruin the experience for us. If your beer tastes like paint thinner or nail polish, you have alcoholic off-flavors. What caused this? Most likely, fermentation at too high a temperature. Take all possible measures to maintain fermentation at the recommended temperature for your recipe’s yeast strain. If possible, aim for a slightly lower surface temperature in your carboy than the recommended temperature, as the middle of the wort can be 10°F (6°C) hotter.
2. Metallic
Unless you enjoy the taste of metal in your mouth, no beer style should taste metallic. If your beer tastes like you bit your cheek or licked a frozen pipe, chances are you won’t enjoy it. So, how did this off-flavor end up in your beer? It likely came from metal, which is called “metal contamination” in the brewing world.
The best way to prevent this is to use stainless steel components. If you make that investment, be sure to take good care of your equipment. Avoid using a steel brush to clean stainless steel components and never let them come into contact with bleach.
If you are on a tighter budget, aluminum can also work, but you may want to avoid guesswork by seasoning the pot with boiling water for half an hour.
If you have an unfiltered well, your water may contain unwanted metals. In that case, save yourself the trouble and use bottled water.
Surprisingly, another suspect that can cause this off-flavor is malt, especially when improperly stored. Your best bet is to find a reliable supplier and brew soon after getting the malt. Avoid leaving it on your shelf for too long, and store it in a cool and dry place.
3. Diacetyl
Beer and popcorn can be a perfect combination, as long as they are separate. If your beer tastes like popcorn, unfortunately, it is likely off. Diacetyl, a common off-flavor, is the culprit. Unfortunately, it is produced in all fermentations by all yeast strains. Like many things in life, when you have too much of a good thing, it becomes bad.
Diacetyl is produced early in the fermentation process and is caused by a high initial fermentation temperature. If the temperature is too high, yeast overproduces diacetyl and cannot absorb it in time. In a normal fermentation with controlled temperatures, the yeast will absorb the diacetyl by the end of fermentation. It can also be caused by malolactic fermentation, where malic acid converts to lactic acid before converting to diacetyl.
In some beers, a small amount of detectable diacetyl is desirable. If you want to continue brewing beer, here are some things to monitor during fermentation:
- You may consider incorporating a diacetyl rest in your fermentation process. In the last three or four days of fermentation, increase the temperature by 3-4 degrees F (1-2 degrees C). This encourages the yeast to do a final clean-up and absorb any remaining diacetyl.
- Be patient with primary fermentation. Notice that all my recipes have a primary fermentation period of 14 days. One reason for this is that yeast plays an important role in removing excess diacetyl from your beer. However, it needs time to do its job, about a week after it reaches the final gravity.
- Pay closer attention to sanitization. Bacteria can also cause this off-flavor. If the previous two tips do not apply to your case, it is likely due to a sanitization issue.
- Store your bottles in a cool area. If your beer is stored at a warm temperature for too long, it can result in higher levels of diacetyl.
4. Estery
This one is a bit tricky because it is not automatically considered an off-flavor. It depends on the beer style. Esters are created during fermentation and taste like bananas, pears, anise, or even rose petals or bubblegum. They add a fruity taste to beer. This flavor is desirable in a Hefeweizen or many English ales (to a lesser extent) and Belgian ales, but not in a Pilsner or an American IPA. If you find yourself with a beer that should not have this flavor, here are some options for the next batch:
- Ferment at a lower temperature. The higher the temperature, the greater the chances of producing a beer with high ester levels (or diacetyl, as mentioned above).
- Make sure you pitch enough yeast and aerate your wort. Insufficient oxygen can contribute to an estery beer.
- If you used an English Ale yeast strain, try using an American one instead.
5. Oxidized
The only time you want oxygen in your beer is when you are adding yeast. After the initial fermentation (about 3 days), oxygen becomes an enemy. Oxygen gives beer a stale flavor profile because it degrades alcohol and aroma.
This off-flavor is often described as wet cardboard or stale. Sometimes it is also described as a sherry-like taste, which doesn’t sound as bad to me. However, most of the time, it is not the desired flavor, so it is considered an off-flavor.
Once primary fermentation is complete, avoid oxygen as much as possible. But don’t stress over it; it is nearly impossible to make homebrew without introducing even a small amount of oxygen. Try your best to avoid splashing the wort when transferring it from the fermenter to the bottling bucket, and again when transferring it from the bottling bucket to the bottles. Always rack (siphon) your beer instead of pouring it from one vessel to another.
6. Yeasty
Just like with alcohol, sometimes an excess of yeast can make your beer less desirable than intended. Some beers are expected to have a yeasty taste, but if you are making a pale ale, it is probably not a flavor you want. Remember to pour gently to leave the yeast behind. If that was not the cause of the off-flavor, you may have bottled your beer before fermentation had finished its work. In that case, the yeast would have remained suspended in the beer. On the other hand, leaving your beer on top of the yeast cake (the sediment) for too long can lead to autolysis, where yeast cells self-digest.
