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I've brewed a number of all grain beers and have been reading a bit about decoction mashing. However the explanations I've read have been a bit complicated.

How do I do a decoction mash?

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why the down vote? – Nathan Koop Nov 17 '10 at 18:07
up vote 3 down vote accepted

A decoction mash is removing a portion of the mash from the rest, boiling it, and then adding it back into the mash to raise the temperature. It's something akin to today's step mashing. However, you can get better efficiency doing a decoction mash as boiling the grain's cell walls are destroyed and allows for better access to the grains starches by enzymes. Here's a link for volume calculations for decoction mashing.

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How do you decide which "portion" of the mash you remove and boil? Do you remove the liquid part and boil it? Or do you remove a mass of soggy grains and boil that? I've had a hard time understanding decoction mashing in the past because "boiling" seems like a strange term to use to describe heating up a mass of soggy grains. – Jeff Roe Nov 9 '10 at 0:39
I'm confused as well. Wouldn't boiling some of the grains extract tannins? – Jeff L Nov 9 '10 at 0:54
It's exactly what it sounds like. You scoop out part of the mash (liquid and grain) and boil. Just like it sounds. When I decoct (which isn't often) I stir the mash up well and then start scooping. And yes you theoretically are extracting tannins, and it may seem counterproductive; but it works. Keep in mind though that decocting was done in the old days because of poorly modified malt. Today's malt is well modified and it isn't really necessary to decoct. – Matt Utley Nov 10 '10 at 0:59
You are advised (e.g. in Palmer's How To Brew and others) to take the thickest portion mash possible. I.e. less liquid, more grain. As for tannins and whether decoction is necessary -- the flavour difference from boiling up the grains is definitely noticeable if you do it right. You are adding malty, caramel flavours. Nice, worth the effort for an Alt or something like it :) – CJBrew Nov 10 '10 at 16:02

A decoction mash will not extract tannins because the pH of the mash is too low. For a single decoction, you boil the grain, leaving as much of the liquid behind as possible. The enzymes remain in the liquid, not the grain, so you will not denature them by boiling. If you do a second or 3rd decoction, you include more liquid. At that point, conversion is pretty much done and denaturing enzymes isn't much of an issue. Contrary to brewing myth, pH is much more of a factor with tannins than temp. the effects of decoction are very debatable. Many test have found that tasters don't really find a difference (or improvement) in flavor from a decoction. Here's one experiment I did. Start on pg. 25...


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Here's a page with probably everything you'd want to know about decoction mashing:


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