Hey gents - de-lurking to post my reply to a similar thread:
A 90 minute mash will give you a slightly more fermentable wort, and if used in conjunction with slightly thinner mashes (1.5-1.75qts/lb) I'd argue that it'll give you better extract if properly managed. e.g. 10 minute solubilization, 20 beta, 35 both, 20 alpha, 5 min mashout more evenly distributes the enzymes, gives the starch bodies more time to absord liquid (and thus become more accessible to enzymes) and give the enzymes more time to work on the starches.
I've noticed very good results when I combine the above time schedule with generous amounts of time dedicated ONLY to beta amylase (BA - 131F-145F) followed by a raise to alpha amylase (AA - 155F-165F) through decoction. My research (and personal experimentation) indicates that the decoction, when supported with small water addition, improves extract efficiency. Based on lit, this is due to the gelatinization of barley starches which then improve the amount of starch available to AA which chews right through them.
Taking gelatinization into account, I think the best way to increase EE on a HB level would be to crush fine and mash in medium-think&low (108F) stirring like the dickens for about 10-15minutes to solubilize enzymes etc. Bring the temp up to 135F (BA) with a medium-thin mash, hold for 15 minutes stirring once, pull a THICK decoction, decoct to raise temp to 140-145F (BA-w/access to gelatinized starches), hold for 30 minutes stirring once or twice, decoct THICK to Alpha temps (150-159F) hold for 30 minutes, stirring once or twice and mashout & sparge.
The below post on HBD does a very good job of breaking down the process, as well as providing a very complex commercial mash schedule designed to maximise ectract efficiency.
See:
http://hbd.org/hbd/archive/4755.html
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As for my usual procedure, I typically pull 75-90% of the grain after the b-amylase rest, ramp up to 150F+ and hold for 20 minutes and boil for at least 30 minutes. I pull almost NO liquid with the grain and take care to strain it a lot. Its kind of a pain stirring for the first 30 minutes while its heating up, but once it hits boiling temperatures I only stir a little bit as it roils pretty well.
The purpose of decoction is two-fold: 1) to darken the grain and encourage melanoidin formation (which will result in maltier and roastier flavors for your beer) and 2) to raise the temperature of the mash without the need for adding more liquid. Note that melanoidin formation takes quite a while at boiling temperatures so 30 minutes of boiling is the MINIMUM amount of time for a proper decoction. As per above, I've also noticed some benefits in terms of efficiency as well as color and flavor. Others using the above formula have reported similar gains in efficiency, if not flavor. I think the typical efficiency for the procedure outlined above is 92% as an average of my data and information gained from other brewers using that mash schedule. My peak was 96% and low was 88%.
Nick "TheMadMasher" Zeigler