Acid Rest Question

[philm63]

Doing a Hefeweizen this weekend and I plan to mash-in at 111 F for a ferulic acid rest for 10 minutes, then pull a decoction.

My question is this: When doing any "acid rest", the mash will become slightly more acidic, yes? But how much more? Will it keep going, or is there some sort of buffer effect that dictates after it drops a certain amount, it can drop no further?

Bru'n Water calculations show that at mash-in, my pH should be around 5.5, and I'd like it to be around 5.2 during conversion. When I do my rest at 111 F, will I see enough of a drop before pulling my decoction, or should it take longer? Should I just add a few ml of 10% phosphoric instead of waiting around for the pH to drop on its own?

[reverseapachemaster]

I don't think the ferulic acid rest will drop ph that much. The purpose of that kind of acid rest is to develop the precursors to the clove phenol rather than adjust ph. I'd check ph after you return the decoction and be prepared to make a ph adjustment to 5.2.

[kramerog]

The ferulic acid rest is within the phytase rest.  The phytase (acid) rest is done to lower the pH.  But according to Palmer, "The acid rest is not used nowadays because it can take several hours for this enzyme to lower the mash pH to the desired 5.0 - 5.5 range." See http://www.howtobrew.com/section3/chapter14-2.html.

[philm63]

This is what I was afraid of - the pH would take hours to drop into my desired range for conversion. I'll adjust with phosphoric after the decoction is added back to the mash for the sacc rest.