Buttered Popcorn or Butterscotch (diacetyl)
Diacetyl is a natural by-product of fermentation. Diacetyl in very low amounts (50 parts per billion) will impart smoothness to the beer. A bit more diacetyl in your beer will taste a bit like butter or butterscotch. Artificial butter is made with diacetyl, but ironically butterscotch itself usually has no diacetyl. Slightly more diacetyl and eventually your beer will be undrinkable.If you’ve ever noticed a slippery butterscotch flavor in Chardonnay wines, it’s because they have a bit of diacetyl inside. Unfortunately recent trends have been to allow too much. These are the wines many refer to as “butter bombs”. Many ales have butterscotch notes which are quite nice.
Buttered popcorn is a great snack, but it's a really bad beer flavor
When the butterscotch becomes too much, the beer starts to taste like buttered popcorn. Diacetyl is produced during the fermentation process, but usually is reabsorbed by the yeast. If the yeast is interrupted, goes into dormancy too soon, or the fermentation stalls the yeast will not have a chance to reabsorb the diacetyl.
You can also get diacetyl from bacterial infections. If you have other “symptoms” such as sour flavors, strange looking bacteria in the wort, etc… then you need to revisit your sanitation procedures.
Your beer can get diacetyl flavors if you pitch too little yeast or old yeast. The reason is there might not be enough yeast at the end of the fermentation to reabsorb the diacetyl. If the yeast dies or flocculates before absorbing all the diacetyl, the remaining diacetyl will impart flavor to your beer. Sometimes this is a desired effect, other times not so much.
Diacetyl problems unrelated to bacteria can be corrected before bottling/kegging with a diacetyl rest. A diacetyl rest is warming up your lager at the end of the fermentation so the yeast can wake up and absorb the diacetyl. If you are making a lager, move the carboy to a warmer location and let the yeast finish their work for a few days. Since ales are usually at a warm temperature, leave the ale alone for a few days more until the flavor goes away.
- Perform a diacetyl rest at the end of your fermentation – for lagers increase the temperature
- Pitch proper amounts of yeast – old yeast or too little yeast can cause these off-flavors
- Don’t rack too soon – if you rack before the fermentation is complete, the yeast cannot absorb the diacetyl
Band-aid flavor (phenols)
The band-aid flavor is usually caused by a reaction of phenols with chlorine. Chlorophenols are created when phenols react with chlorine from bleach or other chlorine-based cleaners. These molecules can affect the taste in single parts per billion – tiny amounts can ruin the flavor of your beer.If your beer has the dreaded band-aid flavor, you are introducing chlorine into your beer at some point in your process. The chlorine can come from you city’s tap water or possibly your cleaning solution. If you are using a chlorine-based cleaner, make sure you rinse your equipment thoroughly with boiled water. A better solution is to never use chlorine to clean your equipment.
Some wild yeast can produce this flavor, but it is more likely the problem is coming from chlorine. If you are practicing good sanitation techniques, the first step to correct this problem is to eliminate every possible source of chlorine. Make sure your sanitizers are not using chlorine and use filtered water.
- Chlorine-based sanitizers mixed with phenols produced by fermentation
- Some yeast strains, such a Bavarian, will produce some clove-like phenol flavors which are desired
- Too much chlorine in your city water can give this flavor
- Don’t use chlorine, instead opt for a no-rinse sanitizer like StarSan
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