Average Gravity

During both world wars, there were limits on the strength of bee, But it seems to have wirked in a subtly different way.

I'm still struggling to find all the WW II rules. It's very frustrating. Whereas those from WW I I have in full. I recently bought "The Brewers' Almanack 1961-52" hoping that it would at least summarise them. As editions for the 1930s had those from WW I. No such luck.

I'm still scratching around for fragments like this.

"Average Gravity:
The Society had been asked to deal with the case of a brewery who, having failed to keep within their permitted average gravity, as reduced by 15% below their 1939 figure, proposed to brew a certain amount of very weak beer not for sale.

The Committee unanimously recommended that the Council should condemn such a proposal, which was directly contrary to the national interest in wartime. The brewery in question had stated that beer was coming into their district at considerably higher gravity than they were permitted to brew, and that this was having" an adverse effect on their trade. All brewers, however, were subject to the 15% reduction in average gravity and it necessarily followed that, if strong beer were coming into the area now, it was also coming in before the war. The Committee had observed that the average gravity of the brewery in question was not unduly low and there were a great many breweries whose permitted average was considerably lower."
The Brewing Trade Review, November 1943, page 325. 

In WW I, the same average gravity applied to all breweries, where as in WW II it was on a brewery by brewery basis. So if your average had been high pre-war, it would remain relatively high.

The 15% reduction in OG was implemented because of the allocation of materials ti brewing. 15% fewer than used in 1939, without a reduction in the volume if beer brewed. As you can see in this tavle:

UK beer production and strength 1939 - 1946
Year	Production (bulk barrels)	Production (standard barrels)	Average OG
1939	24,674,992	18,364,156	1040.93
1940	25,366,782	18,738,619	1040.62
1941	26,203,803	18,351,113	1038.51
1942	29,860,796	19,294,605	1035.53
1943	29,296,672	18,293,919	1034.34
1944	30,478,289	19,193,773	1034.63
1945	31,332,852	19,678,449	1034.54
1946	32,650,200	20,612,225	1034.72
Source:
Brewers' Almanack 1955, p. 50 and 57

Brewing weak beer that you weren't going to sell just to get your average OG down was taking the piss. And a waste of the materials used.