Had you thought of porridge oats
I wouldn't use oats personally. Yes foam relies on protein, but oats also bring a lot of oil that kills head - and personally I'm quite sensitive to the flavour of them too. That's not to say they can't help in small amounts, but they would be a long way down the list of things to try.
It's worth noting that the
Greene King website only lists malt barley as an allergen, so they're not using torrefied wheat, which is more of a northern thing for beers poured through a sparkler.
So one thing to consider is - just how much foam are you looking for from a beer that is traditionally served on cask, without a sparkler?
Another thing to consider is just how clean your glassware and other equipment is, which can make a big difference as any fatty residues will kill foam. Is it
beer-clean?
I'm going to try adding Torrified wheat to my Old Speckled Hen recipe when I next brew it, to try and help the head retention in a Corny Keg.
Can anyone advise on quantity to try?
My normal grain bill for a 23L brew in my Brewzilla Gen 4 is 3.4Kg Pale Maris Otter & 340g Crystal Dark.
Bear in mind that 9% dark crystal is a lot, and will be very bad for foam. Don't make the mistake a lot of USians make with British beer, of trying to hit a colour target just with speciality malts - there's usually a lot less than people think, with the colour being made up to a standard with a variable amount of (near-flavourless) caramel. So personally I'd knock that down a bit.
+1 to a glycoprotein rest
Supposedly OSH is fermented up to 24°C (75°F) - it's hard to replicate that exactly at homebrew scale as the yeast works differently in smaller volumes, but there's certainly quite a bit of ester character there and I wouldn't be afraid of going up to 21-22°C.
