Okay. Back now.
Brown malt historically was simply excessively-kilned pale malt. We think it had about as much diastatic power as modern Munich malt. Modern brown malt has no enzymes to speak of, because of the modern method of kilning.
Modern malts are, except for a very few quaintly traditional British floor maltings, produced by kilning in a drum roaster. Until the drum roaster was invented in the early 19th century, all malt was kilned on the floor.
Brown malt was much less expensive a raw material than pale malt. Brown malt took less care to produce and could be gathered from the leavings of pale malt production. Porter brewers, with their immense production pressures, wanted to keep the bottom line as low as possible. Thus Porter and Stout brewers tended to use Brown and Amber malts exclusively in their grists.
The London & Country Brewer tells us (in 1736):
The brown Malt is the soonest and highest dryed of any, even till it is so hard, that it's difficult to bite some of its Corns asunder, and is often so crusted or burnt, that the farinous part loses a great deal of its essential Salts and vital Property
Anyway, it still had sufficient diastase to convert itself. The bulk of the grist would have been pale malt. By 1850, brewers had realized that the increased extract from pale malt more than made up for the higher per-unit cost. Combined with highly-roasted malts then becoming widely available through drum-roasting, and Porter as we know it today became possible. For example, the Barclay-Perkins Porter grist from 1851 was 85% Pale Malt, 12.12% Brown Malt and 2.88% Roast Malt, to OG 1057, and hopped at a rate of 3.25 lbs per bbl. The apparent extract of the 1851 beer was ~82%, compared to the 1805 Porter at ~64%; the 1805 beer had 56.23% Pale malt and 43.77 Brown Malt. See the difference in extract percentages?
Anyway. Historical brown malt is not commercially available. You really do have to make your own to replicate historical beer. That is not to say your beer is going to suck! It just won't be as meticulous as a nutjob like me would brew.
But then again I make my own
essentia bina when I brew Porter...
Bob
