Decoction verification: boiling the grain?

I watched the sticky thread with the 3 videos (thanks Kaiser!) about the Decoction mash, but I may have missed the part where it is explained (or not?) about boiling the decocted mash.

If I understand it right, I'm drawing off grain and liquor from the thicker (more grain) or thinner (more liquor) part of the mash depending on the recipe/prescribed mash schedule, then putting it into a pot and brining it to a boil if prescribed?

Can someone explain how I can reconcile my fears of boiling grains with how a decoction mash is supposed to happen? It is counter-intuitive since I've learned for the last year or two that overshooting mashtemps past 170 can lead to excessive tannins from the grain husks getting into the liquor, causing astringent flavors.

The sugars that are still in the solution in the decotion will act as a buffer so you'll avoid extracting tannins. When you're sparging, you've removed most of the sugars and hence no buffer and the reason to stay below 170*. I wondered the same thing about decotion mashing until I read about it in Brew Science.

Tannins don't come from temp alone...pH is a far bigger factor. The pH of the mash is generally well below what it would need to be to extract tannins, so there's no worries about boiling grains for a decoction.

And, BTW, if "Brew Science" says it's due to sugars, that's some questionable "science"!

Denny said:

And, BTW, if "Brew Science" says it's due to sugars, that's some questionable "science"!

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Technically, it's the sugars that result in the lower pH during boiling, so I think it's safe to say that the "science" is sound.

That's interesting. For my edification, could you explain how that works?

Denny said:

For my edification, could you explain how that works?

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Because of the buffering capability of the decoction mash, the pH does not does not rise to the point where tannin extraction is possible. When lautering, however, the buffering capability of the mash is decreased, since the sugars, phosphates and proteins are being washed away. Briggs discusses the effect of lautering on the pH of the mash on page 116.

While those more intelligent than me debate the science, I'll just throw out there that you want to pull the decoction from the thickest part of the mash. You don't want to use mostly liquid, you want mostly grain. (Again, this goes back to the pH of the decoction).

Hophazard said:

When lautering, however, the buffering capability of the mash is decreased, since the sugars, phosphates and proteins are being washed away. Briggs discusses the effect of lautering on the pH of the mash on page 116.

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Thanks, I understand all that with the exception of how sugars figures into it. What book are you referring to? Brew Science? I'm afraid I'm not familiar with that.

EDIT:OK, I see Brew Science is a forum here. Can anyone give me a link to the topic we're discussing? I'm still kinda skeptical....