If you’re an extract brewer, steeping specialty grains is a simple, yet effective, way to give your homebrew a flavor boost. But you need to be aware that you can introduce off-flavors into your beer by steeping grains incorrectly. Specifically, you can get an astringent flavor, which can vary from a slightly bitter flavor to a strong sour flavor akin to sucking on a tea bag. The astringency comes from tannins, which are a polyphenol extracted from grain husks.
Since all beers are made with grains, some tannins exist in every beer. In most cases, the tannins remain below the flavor threshold. However, you can get an excess of tannins by steeping specialty grains at too high a temperature or with too much water.
Temperature
To avoid excess tannins, you need to maintain the temperature of your steeped grains below 168°F (76°C). Going higher will leach tannins into your wort. In addition, it’s a good idea to use a muslin or nylon mesh bag to contain the specialty grains as you steep them. This will keep the crushed husks contained and out of the boil. (If husks are boiled, they leach tannins.)
Water
A similar effect occurs if you steep your grains at too high a pH value. Specifically if your water/grain mixture reaches a pH above 6.0, you will leach tannins into the wort.
Most water sources are slightly alkaline in pH. Both surface and ground water sources are alkaline, with a pH above 7.0. The specialty grains you use for steeping are slightly acidic, which means that they will lower the pH of the wort when you steep your grains. You run into pH problems when you use a large amount of water relative to the amount of grains when steeping.
For example, if we take the simple approach and steep just two pounds (1 kg) of specialty grains in 4 gallons (15 l) of water, it is likely that this small amount of grain will be insufficient to lower the pH below 6.0, and we’ll end up extracting tannins. Conversely, if we limit the water to 2 quarts (2 l) per pound (454 g) of grain, it is highly likely that the specialty grains will have sufficient acidity to reduce the mixture below a pH of 6.0, which will significantly cut down on tannin extraction.
So to summarize, you need to limit both the temperature of the water and the amount of water used when steeping grains. Specifically, I recommend steeping below 168°F (76°C) (and using a mesh or nylon bag to contain the grains) and using no more than 2 quarts (2 l) of water per pound (454 g) of grain. I also limit the time of the steep—usually no more than 30 minutes.
For tips on crushing specialty grains and deciding how much specialty grain to use, see “Getting the Most from Specialty Grains.”
PHOTO: MATT GRAVES