Thu May 14, 2009 2:38 pm
Yeah, Jamil discusses the loss of foam due to excessive blow offs and then goes into the bit about shaking, transferring, rousing and other things that can coax the foam out of the beer before its time. Check at the 40min mark in the Brew Strong Head Retention show.
To paraphrase he says, "...the head forming protiens are only used once. So it delivers the head and once it's done, it drops to the bottom and it's no longer available to form head again."
I think with a kegged beer, it's probably not too big a deal since any loss is averaged out over all the beers in the keg - much like loss due to a blowoff would be. However, in a blowoff situation you're probably dealing with a beer that's on the extra foamy side, whereas a smaller beer might exhibit more loss from transfers, shaking, etc...
With this beer, I hooked up the cold keg at about 16psi, and put it upright in front of me. I sat in a chair and just shook the top of the keg - enough to get that little bit of headspace moving around. As I shook I could hear my regulator letting in more gas. I shook like this for 5 minutes and then turned the whole keg upside down to mix things up thoroughly. After leaving it in the fridge for a half hour or so, I tried shaking again at the suggested pressure from How to Brew and could hear that hardly any CO2 was entering the keg as I shook. few hours later, I hooked it up and drew a small glass. The beer was cloudy with yeast and dryhops, but was very well carbonated and had decent head retention, considering all the nucleation sites in suspension. In only a 1.039 beer this seemed pretty impressive.
The other thing that surprised me in the Head Retention show was the suggestion to get the beer off the yeast - particularly the yeast sediment in a keg if the beer has been inside for a long time. I don't know that I've experienced this kind of loss, but it has me considering transferring the beer into a new keg once it's pouring clear.
