Enid Porter’s Cambridgeshire Customs and Folklore mentions a Harvest Beer recipe brewed in Weston Colville, a village about 13 miles west of Cambridge, at the brewhouse for the last time in 1946.
6 gallons of water, 2 bushels of malt, 2 lb of hops. The water was boiled in a large copper then transferred to the mash tub and left to cool for one hour. The malt was then added and the mixture closely covered so that it retained its heat for seven hours, after which it was strained and returned to the copper to be boiled, with the hops, for three hours. The liquid was then strained off and, after yeast, previously mixed with a little warm milk, had been added, was left for three days before being placed into casks. These ingredients made 36 gallons of beer
Simple. Except I can’t work out how 6 gallons of water would produce 36 gallons of beer?
Here’s an earlier Harvest Beer recipe from 1883