We had an interesting discussion on mashing time last fall, but it did not cover mashing time vs. diastatic power. I bring this up after reading a bit about low diastatic mashes requiring more conversion time in Strong's 'Brewing Better Beer'.
In the discussion of Ingredients (pg 108), Gordon mentions that mashes with lower diastatic power may require more time to convert. Intuitively it makes sense, but I had not heard it before. The general concensus is that the average diastatic rating of the mash needs to be at least 30 to 40 Lintner to provide complete conversion. I'm more inclined to believe its 35 to 40 Lintner minimum based on Gordon's information.
Given Gordon's statement and the fact that base grains are easily over 100 Lintner, is there really a difference in the time to a negative iodine reading with respect to the average Lintner rating of the grist? I did a brief search, but do not find guidance from anyone having performed such a study. Clearly, a grist with its average diastatic rating
above 100 Lintner will have plenty of enzymatic power to convert, but is it going to convert faster than a grist with 35 Lintner?
Another curiousity is how the average diastatic power is calculated. Since diastatic power is only needed to convert starches, is there any reason to include the weight of grains such as crystal malts in the calculation of the average diastatic rating for the grist? Dilution by those grains is one thought, but I'm not sure its valid. I'm thinking that the total sum of diastatic power divided by only the total weight of STARCHY grain and adjuncts might be valid. This is in contrast to the total diastatic power divided by the total grain and adjunct weight.