Wondering what "slack" means in this context? Damp. That's the problem with roasted malts: they're hygroscopic. Leave them lying around too long and they'll soak up moisture. It's not the first time I've seen a recommendation for buying in a small stock and using it quickly. But recommending slack pale malt be recycled in this way is new for me. I suppose it makes sense.
The apparatus consists of a perforated cylinder, turning easily on bearings, and fitted above a fireplace enclosed in sheet iron, which is extended upwards, so as to form a chimney to carry away smoke, steam, or fumes. The cylinder holds one or two bushels of corn, and should be kept revolving steadily. There should be a low coke fire at first, and afterwards, as the steam passes away, a brighter one. In thirty minutes a fine aroma steals from the malt, which should be inspected five minutes later, by which time a good chocolate tinge ought to have been acquired. In forty minutes tho operation will be completed, and the charge may be turned out to mellow. Mr. Stopes also pointed out that slack pale malt may be more advantageously used in this way than by redrying it for ordinary use.
This plan certainly involves trouble, but the advantage of using the roasted malt fresh is very great. Manual labour for turning would perhaps prove somewhat expensive, but moderate hydraulic power would perhaps do better than power got from the ordinary shafting.
The Manufacture of Black Malt.— Black malt is manufactured by placing ordinary malt directly into roasting drums and scorching it to the desired type of colour, without any previous moistening. According to practical experience it is advisable to have the black malt drums of such dimensions that about 2.5 cwts. of malt may be scorched in one operation. The drums may be heated by open fire, and for carrying off the gases of the lower one. The material is first heated in the upper drum, revolving about 9 to 10 times a minute. When the malt begins to show the first tints of scorching, the process is continued and finished in the lower drum over the direct fire until the desired depth of colour is reached. The lower drum makes 11 to 12 revolutions per minute.
In black malts roasted dry in this manner the husk is strongly overheated, which causes a profound modification of the husks. These black malts thus often acquire a burnt or empyreumatic odour and taste. To avoid these faults it is considered expedient to prepare black malt not from dry but from moistened malt. Instead of moistening malt it is just as good to use half finished kiln malt. In fact, black malts prepared from malts with a higher moisture content show a more uniform browning of the mealy body. The taste also remains milder, the husks being modified to a less degree and hence less quantity of bitter substances formed."
"Brewing and Malting" by John Ross Mackenzie, 1927 , pages 255 - 256.
Empyreumatic. There's that word again. I seem to remember last time it came up that we agreed it means burnt. Odd that it's considered a fault. I thought black malt was meant to taste burnt. Crispy golden black. just like bacon.