Decoction Mash how much of the mash

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The nominal amount is 1/3 of the mash. In reality a bit more, like 35-40%, tends to work better as far as hitting temperatures. Use the total weight of the mash to figure your decoction pull, that is the combined weight of the grain and the water. For example, if you mash in with 10 lbs of grain and 10 qts of water you have a total mash weight of about 30 lbs which would give you an 11-12 lb decoction pull.
 
Michael Dawson does it on that BTV episode. He mentions being taught the decoction mash by a decoction guru who always uses the following rule. One quart of thick mash for every pound of grain in the grain bill. 13lb grain bill, 13 quarts of thick mash should go into the decoction.

I've never done it, but I plan to do so in the near future. When I do go for it, I'll be using that rule of thumb.

JER
 
Generally, you need to pull as much thick mash as you need to hit the next rest temperature. Brewing software (or great math skills!) is extremely helpful for this.

If you pull too much, you can overshoot your temperature when you put it back in the mash. If you don't pull enough, you can miss your temperature also.

I don't think I've EVER done a 13 quart decoction, though! That's a lot.

Normally, if I'm doing a protein rest, I'll do it on the high end (like 131 degrees) and then almost immediately pull the first decoction as I don't want to stay long at protein rest temps (I use well-modified malt). Then I hit the first saccrification rest, stay there for a time (30 mins), pull the next decoction for the second saccrification rest, and for the last decoction I pull thin wort instead of a thick mash for the decoction to mash out.

Normally, the amounts are 5-8 quarts or less, in a 5 gallon batch.
 
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