Simply drink some young red wine, suck on a tea bag, or help yourself to a nice big piece of under-ripe fruit. That dry, puckery, thirst-inducing sensation is astringency.
Astringency is sometimes described as tannic, owing to the tannins (polyphenol compounds found in plants) responsible for that parched feeling in your mouth. And while tannins are integral to a well-aged Cabernet Sauvignon, they’re rarely welcome in your homebrew. Several suspects can cause astringency, but the primary culprit is grain. Grain husks are rich in tannins, and under certain conditions, these compounds might make a beeline for your wort. Here are some of those circumstances and how to avoid them.
- Steeping too long, too hot, or too wet. If you steep specialty grains, it’s possible to extract tannins with too much time, temperature, or water. Simply limit the steep to half an hour or so, make sure the temperature doesn’t exceed 168-170°F (76°C), and use 2 quarts of water or less for every pound of grain (4 liters per kilogram).
- Elevated mash pH. If your tap water tastes good, this probably isn’t an issue for you. But if you adjust your water with lots of brewing salts, you may be pushing the pH too high. Buy some pH strips and measure the pH of the mash (not the brewing water) about 15 minutes in. If it’s around 5.2 to 5.6, you’re fine, but if it approaches 5.8 or higher, consider brewing with bottled water next time or incorporating some acidulated malt (Sauermalz) into the grist.
- Elevated sparge pH. This applies primarily to those who practice continuous (fly) sparging. You want the sparge water pH to remain under 6.0, which may require acidification if your tap water is alkaline. A convenient way to do this is to doctor your sparge water with a measured amount of lactic acid, available at any homebrew store. Also, monitor the specific gravity as wort leaves the lauter tun, and stop sparging when it drops below 1.010.
- Sparge water too hot. All the textbooks tell you to heat sparge water no hotter than 168-170°F (76°C) to avoid tannin extraction, but in practice, what matters is the temperature of the grain bed itself. So if your mash regimen includes a mashout step followed by a continuous sparge, then definitely take a look at the temperature of your sparge water. But if you skip the mashout and batch sparge, the temperature of the sparge water really isn’t that critical.
Other less common sources of astringency include hops (but only if your hops contain lots of stems or other vegetal material), spices used in excess, and Braun Hefe, which is the brown scum that floats atop the Kräusen during active fermentation. The latter is rarely an issue (it usually sticks to the side of the fermentor or sinks to the bottom along with the other trub), but feel free to skim it off during fermentation if you think it’s a problem.