Astringency in Beer
Astringency is perceived as a dry grainy, mouth-puckering, tannic sensation (think of sucking on a wet tea-bag). Although astringent flavors may be caused by bacterial contamination, it is usually the result of processing.
There are many causes of process-related astringency: over-sparging, sparging with water above 168°F (76°C), steeping your grains too long, mash pH above the 5.2-5.6 range, over hopping, or boiling your grains can extract excessive tannins from the husks. Milling your grains too fine and poor hot-break removal resulting in too much trub may be sources of astringency as well.
Traditional brewers in Germany have always removed the brown yeast layer floating on the surface during fermentation. They call this layer "braun hefe" or brown yeast. If you've ever tasted it, you will see why you might not want it in your beer. It is extremely astringent and bitter, consisting of yeast, trub, and hop resins. Their open fermenters made skimming this goo off the top relatively easy. For homebrewers using conicals or carboys, this becomes more problematic.
If you feel you must remove the braun hefe from your beer, one method used by many homebrewers is to utilize a blow-off tube and small head space. The majority of the krausen will be blown-off during the most vigorous phase of fermentation. The problem here is beer losses, which may be substantial. There are many factors affecting the amount of blow-off you can expect, including original gravity, temperature, fill level, yeast selection, and wort aeration. The best thing you as a homebrewer can do is to experiment. Try the blow-off method and then brew the same beer without using the blow-off tube. If you notice a discernible difference between the two beers, then you may want to continue using the blow-off tube method.
Most homebrewers don't bother, and brew perfectly good beer. The fact that a lot of the brown goo sticks to the sides of the fermenter and is left there after siphoning the beer to secondary or to the keg, helps most of us too.
In summary, to avoid astringent flavors in beer:
- Avoid "over-milling" your grains. The grain should be cracked open and broken but not crushed or milled to a flour.
- When Sparging, watch your temperature and don't sparge with water hotter than 168°F (76°C). Also, don't over sparge with too much water. Try to stop the run-off when it gets to 1.010. The mash pH is increasing during the sparge and beyond this SG, you run the chance of stripping too much astringency from the grain bed. If you are measuring the run-off pH, stop when the pH rises to about 5.8 to avoid astringency problems.
- When you steep your grains, be sure you don't let the water come to a boil before you take them out.
- If you are adding fruit to your wort, never boil them. Instead, add the fruit to the primary or secondary fermenter.
- Don't add too much hops, or hops with too high of an alpha acid content for the style you are brewing.
- Use a blow-off tube if you feel that allowing the krausen to fall back into the beer will negatively affect the flavor.
- Watch your mash pH, if it tends to be greater than 5.6, try using a pH stabilizer like 5.2 from five-star.
- Make sure you don't allow the hot-break trub to get into the fermenter. Allow the cooled wort to settle prior to siphoning it to the primary fermenting vessel.
Information for this article was adapted in part from The Home Brewer's Answer Book by Ashton Lewis, How To Brew by John J. Palmer, and “Off” Flavors, Their Causes and How to Avoid Them compiled by Robin Wada from More Beer.
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