Post
by McMullan » Tue Apr 06, 2021 11:51 am
Cheers, Eric. I thought you’d like that one.
I think, based on my understanding, Orlando, which is a bit limited for the Burton Union system, the Burton Union and Yorkshire Square are both about managing yeast, but in different ways due to subtle differences in yeast behaviour. Local brewing culture practiced and expectations about the end product, too, of course. The Burton Union is a continuously recirculated system, where top cropping yeast are batch fed fresh wort then cropped automatically as they actively climb out out the fermenting wort, as it passes through the system. They aren’t very flocculant during active fermentation so easily cropped, albeit by a sophisticated system that acts like a filter, in terms of producing fairly bright beer downstream of the process. It’s likely we have to rack off from under these strains at home? By contrast, fermenting wort in a Yorkshire Square gets recirculated periodically for short bursts, after fermentation activity peaks and until it begins to wane or before.* The Yorkshire Square yeast strains are typically highly flocculant, although the most metabolically active cells (younger and more genetically stable?) climb out of the sweet wort, like Burton Union strains do, but they also express bottom fermenting behaviour too. (You’d be forgiven for assuming you had a dual strain culture here.) The problem is they’re so flocculant they soon compact on the bottom of the FV and start to fractionate, where buried layers, with limited access to sufficient wort resources, go dormant, slowing fermentation. So they need a good rousing to get them back in suspension where they can ferment the wort more efficiently. That goes for those that flocculate in the yeast trough too. In contrast to the gentle recirculation in a Burton Union, the recirculation in a Yorkshire Square needs to be quite forceful, to disturb the yeast back in suspension.
*This timing (window) is likely crucial, imo, as during active fermentation, especially at a commercial scale, the yeast produce so much CO2 it acts as an effective barrier to air above the yeast trough. I’m now very skeptical about the idea air (O2) plays a role (boosting yeast performance) during active fermentation in a Yorkshire Square or other systems where wort is recirculated and sprayed back in. If it did, I’d expect Yorkshire Square brewers to start recirculating after pitching yeast, but they don’t. I’m not aware of any data for or against any role for O2, but sticking your head over a Yorkshire Square during active fermentation then taking a good sniff is quite persuasive evidence. But I have heard commercial brewers claiming things like ‘our yeast strain really likes air during fermentation’. I’m not sure if they’re just confused or taking the p*ss.
Life moves on. 
: