Damn it! That the third beer in a row that's underattenuated: only 70% on an IPA, which I had expected to be at least 75% and the result is a FG of 1.019, outside of style specs.

I'm waffling about on how to do step mashes that will control fermentability in the way that I want. As I've already said, I'd like to change they way that I do this to make it involve a single varriable in the sachrification period. I also want to include a protein rest for clarity on (especially) lighter beers.

To move to single variable mashes, we vary either time or temperature but not both in our mashing procedure. One could either decide (following a study cited by John J. Palmer) to do mashes with sachrification periods of 50 minutes and 15 minutes, where the former stage varies in temperature and the later is always 158. Alternatively, one could vary time by always mashing at two stages, say 145 degrees followed by 155 degrees, where the first mash is conducted for a variable amount of time and the second always for 30 minutes, or 45 minutes, or whatever. I think that the second program is actually preferable.

The protein rest at 125 should
-make the final beer clear by degrading large haze forming proteins.
-improve hydration and promote later enzyme activity.

The first sachrification at 145 should:
-promote gelatinization, making later beta-amylase activity more efficient.
-create maltose from beta-amylase activity.

The second sachrification should:
-create maltose and other fermentable sugars by alpha- and beta-amylase activty.
-complete startch conversion.

The mash-out should:
-terminate enzyme activity
-give me confidence that sparge rates and temperature did not affect the sugar profile of the mash because of continuted enzyme work.

The reason is that one knows that a 45 minute mash at 155 degrees acheives complete or nearly complete conversion with a wort that will produce a full body but medium or medium-low attenuation. The addition of the 145 step before hand means, approximately, that one increase the available maltose by beta-amylase activity without any risk of alpha-amylase denaturing. So, approximately, the first sachrification stage just increases fermentability while conmensuratly reducing dextrins that result from the later stage. The only potential problem I see is that the curve is too steep or too flat--i.e. that the difference five minutes makes to the fermentability of the wort is too large for this to be an effective way to control the fermentability of the wort, or that the difference made by a five minutes variation is too small. But my experience with 90 minute low temperature mashes seems to indicate that the curve will have the right first derivative.

What I'd like is for the slope of the curve to approximate a scalar function with 12 minutes difference in the rest-time making a 2% difference in fermentability; that would allow a control of 7.5% fermentability by 45 minutes of mashing. My guess however is that the curve isn't so scalar. Up to about 30 minutes, I think the rate will be fairly constant, beyond that, I think mash starts to approach complete conversion during the initial rest, and this will affect the results of the alpha-amylase rest. I'm not sure whether that's what I'll get, but I'm going to play around shortly to see what results this will get.

Here's the amber ale that I'm making to test this out:
8 # American two-row
.75 # American 80L crystal
.25 # American 20L crystal
.25 # Belgian Special B
.25 # American Victory

Step mashed 125 (20 mins)-145 (30)-155 (45)- 167(5 mins).

Hops:
Northern Brewer.75 oz. (7.6% AA) 60 mins
Norther Brewer .25 oz. (same AA) 15 mins
Willamette .66 oz for 1 mins

Re-pitch with white labs California V ale yeast from previous brew.

I.B.U. 27
SRM 12.5
O.G. 1.048 @ 75% efficiency
F.G. 1.012 @ 75% apparent attenuation

Of course, the real question here is what's the apparent attenuation is.