On this page
http://en.wikipedia.org/wiki/Diastatic_power I found this information:
A malt with enough power to self-convert has a diastatic power near 35 °Lintner
Is it too simple an approach just to calculate a weighted average of the diastatic power and check if the number is greater then 35?
An example:
Pale Malt: 2,1 kg * 100 °Lintner = 210 kg*°Lintner
Munich II: 1,9 kg * 25 °Lintner = 47,5 kg*°Lintner
Carafa I: 0,7 kg * 0 °Lintner = 0 kg*°Lintner
Special B: 0,70 kg * 120 °Lintner = 84 kg*°Lintner
Caramel/Crystal Malt - 60L: 0,60 kg * 0 °Lintner = 0 kg*°Lintner
Weighted average = (210+47,5+0+84+0)/(2,1+1,9+0,7+0,7+0,6) = 57 °Lintner > 35 °Lintner, i.e. sufficient diastatic power.
By the way: In BeerSmith, the diastatic power of Special B is set to 120 °Lintner. That seems way to high for such a dark malt. Is 120 °Lintner the correct value for Special B?