Astringency Primer By: Kay Witkiewicz
If you give your homebrew to 100 different people to try, chances are you’ll receive 100 different opinions in return. Everyone’s palate is unique, which makes tasting and talking about beer with your buddies so much fun. However, one beer tasting aspect neither you nor your buddies should get confused about is the distinction between bitterness and astringency. Bitterness—derived from numerous sources, but mainly hops—provides a pleasant counterpoint to beer’s malty sweetness, while astringency is not so much a flavor as it is a particularly puckering mouthfeel that parches your palate. Bitterness is desirable, astringency generally is not, and with multiple potential causes of the latter, there is plenty to be aware of on brew day.
If you’ve ever squeezed out the dregs of a tea bag and sampled them, then you know what astringency tastes and feels like. Phenols cause this lingering all-encompassing, mouth-puckering sensation. In beer, grain husks and hop stems are the main raw material sources of phenols (also referred to as tannins when discussing astringency), but your water temperature and mineral composition also play significant roles in extracting these chemical compounds. In your mouth, phenols bind with proteins causing the epithelium to contract, creating a puckering sensation. However, over time phenols will bind to proteins in your beer and precipitate out, thus leaving a smoother brew. Extracting phenols is unavoidable when brewing beer, but you can certainly manage the level of extraction.
Water temperature and composition are crucial control points in avoiding astringency. Regardless of your sparging technique, maintaining your water temperature below 170 degrees Fahrenheit ensures that you’re not scorching your grain and thus stressing the husks into releasing undesirable amounts of phenols. Over-sparging—letting your grain steep for too long or infusing your grain with too much sparge water—also increases potential phenol extraction due to increased contact time and surface area exposure between husks and hot water. Hence, finding a balance between your strike water volume and your sparge water volume to achieve your desired pre-boil volume is important. In addition to avoiding over-sparging, make sure to keep an eye on the pH of your sparge. Phenol extraction increases at higher pH levels. Dry harshness is never a good flavor in beer, and in order to protect your homebrew from astringency, you must micro-manage your sparge water.
The mineral composition of your water can further exacerbate undesirable phenol content in your homebrew. Whether you adjust your brewing water with various brewing salts, such as gypsum (calcium sulfate), calcium carbonate, or calcium chloride, or you brew with your water as is, certain mineral contents should be monitored to avoid astringency. The inspiration for this article actually came to me a few days ago when I took a gravity reading and taste test of my ESB (Extra Special Bitter). The water here in Boulder is great for brewing as is, but the calcium level is a little too low for my liking, so I have been adding gypsum to my mash to bump the calcium and consequently the sulfate content of my water, which is also low. Calcium increases permanent water hardness, lowers the mash pH, improves mash enzyme activity, and improves fermentation, while sulfate promotes dry, crisp bitterness, especially in highly hopped beers. High calcium and sulfate contents are the hallmarks of the water source at Burton-on-Trent, famous for creating crisp British IPAs. Rather than adding my usual ½ teaspoon of gypsum to my mash, which bumps my calcium and sulfate contents into the lower half of desirable ranges, I added a full teaspoon for my ESB in order to replicate a more British water profile. In very high concentrations, sulfate turns your beer from dry and crisp into astringent—and that’s exactly what I tasted when I sampled my ESB. Luckily, a few more days in primary and a couple of days of dry-hopping seem to have done wonders because, while the beer may be a touch drier than I wanted it to be, at least it was no longer astringent during bottling. Time heals a lot of homebrew wounds, but in order to avoid scares like this in the first place, be sure not to over-do your water treatment additions.
Although astringency will fade with time, avoiding it in your beer from the beginning is even better. Controlling your water temperature and its mineral contents is the key to limiting the extraction of undesirable amounts of phenols from grain husks and hop vegetal material. Sparging under 170 degrees Fahrenheit for no more than 15 minutes at a water-to-grist ratio of 1:1 or less and at a low pH (around 5.2 to 5.4) should minimize the release of tannins from your grain husks. Furthermore, close attention to your water’s mineral contents is warranted, especially if you adjust your water profile with brewing salts. High calcium levels are desirable to accentuate bitterness and crispness in your beer, but if sulfate levels rise concomitantly—as is the case when you’re adding gypsum to your mash—this dry bitterness may turn into astringency. Once you’ve tasted and felt astringency, you will never again confuse it with bitterness and it’s just a matter of careful water management to avoid it altogether in your homebrew.