This section is from the book "Alcohol, Its Production, Properties, Chemistry, And Industrial Applications", by Charles Simmonds. Also available from Amazon: Alcohol: Its Production, Properties, Chemistry, And Industrial Applications.
Thirty kilos, of rye grist are added all at once to 54 litres of water at 64°. The mash in covered up and steeped for half an hour, by which time the temperature falls to 44°. Boiling water (60 litres) is then added, in order to raise the temperature again to 65-66°. After the mash has stood for a further two hours, cold water is stirred in until the temperature falls to 31°. At this stage pressed yeast (3/4 lb.), worked up with water, is added, the mash cooled by a coil to 19°, and passed to the fermenting-vat. The fermentation is started at 16°, and goes on for five days.
Investigating the yields given by this process with rye and other materials - wheat, barley, oats, maize, buckwheat, rice, millet, potatoes, and artichokes - Windisch and Jetter found that rye was the only grain that contained sufficient diastase to yield as much alcohol without malt as with malt.2 Wheat contains a good proportion of diastase, but not enough to give the full yield of alcohol unless some malt is added. Buckwheat approximates to wheat; barley and oats give lower results. Maize contains only a little diastase, and the raw starch is much less readily saccharified by malt than the steamed material; rice and millet are similar to maize. Potatoes contain only traces of diastase, and the raw starch is only partially saccharified by malt. With artichokes, the whole of the inulin is saccharified, whether malt is used or not, and whether the material is steamed or not.
1 Bull. Assoc. Chim. Sucr., 1917, 35, 237; J. Soc. Chem. Ind. (Abst.), 1917, 36, 1284. 2 Zeitsch. Spiritusind., 1907, 30. 641, 552.
"Brewing extract." - This is a term commonly used by distillers in this country to denote the weight, expressed in lb., of the dissolved material present in the wort. It may be calculated from the specific gravity of the wort thus: -
Let the sp. gr. be, for example, 1047 (water = 1000; it is always taken thus in practice).
Weight of a gallon of water
" " " wort
dissolved extractive matter = weight of wort minus weight of water = 10 47 - 10 = 047 lb.
This is the brewing extract per gallon of wort.
Hence to find the brewing extract for any given quantity of wort, multiply the number of gallons of wort by the expression sp. gr. of wort - 1000 100
Example: - Given 7000 gallons of wort, sp. gr. 1045. The brewing extract is 7000 X 45/400 = 3150 lb. If this has been produced from 300 bushels of malt, the brewing extract per bushel is 3150 % 300 - -105 lb. per bushel. This would be a fair average yield from unscreened malt. From screened malt, the average yield would be higher - about 11 lb. extract per bushel.