Astringency is sometimes described as tannic, stemming from tannins (polyphenol compounds found in plants) that is responsible for that dry feeling in your mouth. The astringent off flavor is characterized mostly by a vinegar-like, puckering taste with a dry taste similar to a high-tannin wine, as well as a powdery or metallic taste. Think the drying sensation you get from sucking on a tea bag.
Whats the cause?
Most commonly the cause is from grain. Grain husks are rich in tannins and under certain conditions they will make it into the wort.
- Elevated mash pH. 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
- Elevated sparge pH. This applies primarily to fly sparging. You want the sparge water pH to remain under 6.0, which may require acidification if your tap water is alkaline.
- Sparge water too hot. All the books ive read say to heat sparge water no hotter than 168-170°F (76°C) to avoid tannin extraction. But what matters is the temperature of the grain bed.