They often made 3 brews from the same batch of dry ingredients. The first pass - with most sugars and body, but least water in the mashing, went to make 'strong ales' at around 6%-8%. Once that was done with they boiled up the inredients again for a mid-strength brew which was usualy around the 4% we find common today. Wasting nothing at all a final mash provided a 'small beer' at 2%-3% which is what this 'new' Guiness could well be!

Cheers

DtG