Tannins are polyphenols found in a wide variety of plants, distributed among various tissues. In a later article, I’ll discuss the basic chemistry of the tannins relevant to brewing. (The types of tannins that end up in beer from the malt are different from those that originate in the hops.) In this article, however, we’ll treat them as a group because they are all related chemically, the factors that affect them are the same, and the consequences if they get in your beer are the same. I’ll discuss tannins extracted in the mash today, and cover tannins in the boil over the weekend.
Review and Background Information
As I mentioned in the previous article on the basics of tannins, tannins are present in all beer and in fact are required for it to taste like beer. In excess, however, tannins cause astringency — a puckering sensation, as experienced when drinking tea, due to these polyphenols binding with salivary proteins. As a brewer, we want to avoid brewing beer that is astringent, so we strive to create conditions during our brewhouse operations that allow this. Extracting tannins from plant products is not an all-or-nothing thing. If a tannic part of a plant is in contact with a water-based solution, tannins are being extracted at some rate. The rate is influenced by temperature, pH and time — the same variables that influence the extraction of any water-soluble compound from any solid. (For example, these variables affect iso-alpha acids extraction from hops in the same manner.)
Most tannins in beer come from the malt. Figures vary, but Kunze — in his text “Technology Brewing and Malting” — gives 80%. However, the hops are also a source of tannins. And, it’s probably safe to assume that Kunze was referring to a German-style beer, rather than an IPA, so 20% may be a lower limit. In addition, spices other than hops and barrels used in aging can add tannins.
Crushing the Malt
As with anything, the more finely you crush your malt, the easier it is to extract things from it. For example, crushing your malt leads to better extract efficiency. On the other hand, it also increases the amount of tannins in your beer. However, the effect is fairly small and — unless you are milling your malt into a powder — it’s best to gear your milling goals towards getting good extraction, while still being able to lauter easily.
Infusion Mashing with Continuous Sparging
In most beers, the majority of the tannins come from the malt. During mashing, the grain husks and aleurone layers — the parts of the barley malt that contain tannins — steep in water at 148 –162 °F (64–72 °C). A “plain” single infusion mash duration can vary from 20 minutes to 90 minutes, with 60 minutes being very common in homebrewing. (The times and temperatures will vary if the brewer performs a step mash.) During the mash, the pH should eventually settle into the 5.2–5.6 range. At this point, small amounts of tannins are being extracted, but not so much as to be problematic. The mash out raises the temperature to 168–170 °C (76–77 °C), and during subsequent running off of the wort, and rinsing the grain bed with sparge water, the pH of the wort in the grain bed rises.
If the pH rises to 5.8 or above, the combination of heat and high pH will cause tannins to be extracted at an unacceptably high rate. This is the major point in the brewing process at which brewers can keep their tannin levels in check. By keeping the temperature below 170 °F (77 °C) and the pH below 5.8, you can keep tannin extraction during wort collection to a reasonable level. Watch the temperature of your grain bed (the sparge water temperature itself is not the important variable) and quit collecting wort when the pH rises above 5.8. In practice, many homebrewers will have quit collecting wort before this point — especially when making big beers, but not employing an extended boil.
Decoction mashing involves boiling up to one-third of the mash — wort, grain solids, and all — and the mash time is typically longer than a single infusion mash. Even though the pH is (or should be) in the 5.2–5.6 range, decoction mashes yield beers with higher levels of tannins. (In the chemistry article, I’ll discuss which tannins those are.) However, employing a decoction mash does not automatically mean your beer will be astringent. As long as your mash pH is in the proper range, tannin extraction should be limited to an acceptable rate.
Batch Sparging and Other Variants
Proponents of batch sparging often cite low tannin extraction as a benefit of the method. Given the temperature and pH values associated with a single batch sparge — often coupled with not collecting all the wort that could be obtained from the grain bill — this is likely true. If you collect two sparged batches of wort — three total, and the volume of wort you collect approaches 0.65 gallons of wort per pound of grain — you may want to check the third wort by taking the pH and tasting it.
There are numerous types of mash programs and sparging options. If you have a thermometer and a pH meter, you can check for yourself if you are in the danger zone for excessive tannin extraction. (One thing I wonder about is overnight mashes. This hasn’t been studied because it isn’t done commercially, but the extended time the malt is soaking in hot water makes me wonder about tannin extraction.)
The Bottom Line for Mashing and Sparging
Whatever combination of mash program and lautering method you use, the proof is in the pudding. If you can’t detect any astringency, then your brewhouse procedures are fine for you. If you have someone in your homebrewclub that’s good at detecting astringency, let them sample your beer to get more info. Overly astringent beers are not a common problem in homebrewing, but they do crop up occasionally. Knowing what variables affect them will help you to stay away from circumstances that could result in tannic beers.
In the second half of this article, we’ll see how tannins are extracted from hops during the boil and how tannins are precipitated in the hot and cold break. In a later article, I’ll deal with the chemistry of polyphenols in a little more depth.