Perhaps the effect of maltodextrin (this is what I was drinking last night)?
View attachment 61776
The head is obvious! You'll just have to take my word for it having loads of body. This is dextrin from a warm mash and using a "dextrin adverse" yeast. Mashed at 66°C for 70 minutes, so not particularly unusual
but it was Chevalier "heritage" barley malt which needs careful handling (and allows the mash outcome to be easily controlled). Mash-out was 30 minutes at 69°C before ramping up to 75°C but I'm beginning to doubt the usefulness of those last steps. The recipe is from Ron Pattinson's research; an 1804 Barclay Perkin's TT (Porter!) containing only three malts: 46% Brown, 14% Amber and 41% Pale.
No Black 'cos it wasn't invented until 1817. And the malts are my "emulations" of historical malt 'cos "modern" brown and amber malts in these quantities would be nasty. Wyeast #1099 yeast (rated 68-72% attenuation).
Chevallier barley malt was available until 1820, but it's too useful for manipulating dextrin content (and 1975 MO would be well out of order!). Despite the "manipulation" FG got down to 1.016 (the 1804 notes were 1.015, so not bad really?). OG 1.054 (quite weak for a 19th Century porter), 67 IBUs (they did like a few hops back then). No "Brett" (next time perhaps?).
Served at ambient temperature, free-flow tap, 5.5PSI (a bit high) and
no nitrogen!