My reply was that the low gravity was connected with the war and later went back to the classic 1100º+. Want proof? Well, obviously, I've got plenty. From a couple of different sources.
Russian Stout was extremely unusual in being almost exactly the same gravity in 1986 as in 1847. I can't think of another beer that managed to get through the two World Wars with no drop in gravity.
If you're wondering why the rate of attenuation is greater in the examples from 1938, 1950 and 1953 is greater, the answer is simple. Those are analyses of the finished beer, after the secondary Brettanomyces fermentation. While the others are taken from brewing records and the FG is at the end of primary fermentation.
|Imperial Russian Stout 1849 - 1986|
|Barclay Perkins brewing records held at the London Metropolitan Archives, document numbers ACC/2305/1/540, ACC/2305/1/542, ACC/2305/1/544, ACC/2305/01/611, ACC/2305/01/614, ACC/2305/01/621.|
|Whitbread Gravity books held at the London Metropolitan Archives, document numbers LMA/4453/D/02/001 and LMA/4453/D/02/002.|
|Good Beer Guide 1982 and 1987.|