I know that 1450 was one of them. But Shellhammer’s original research was done with a light lager IIRC. Also, IIRC, it was done with a finished beer.
I agree. I guess I should ‘clarify’ ([emoji23]) my statement of “after fermentation” to mean [after the beer had dropped bright and been taken off the yeast].
Dr Bamforth explained that if the beer is oxidized it can be “run through yeast” to clean it up. Therefore, we know oxygen is consumed by yeast.
No dogma intended. …but I stand by my (clarified) statement: “[after the beer had dropped bright and been taken off the yeast], O2 is one of the mortal enemies of beer. Heat and light are two others.”
I recently read something posted by Stan Heironymous stating that the term “dry hop” may have come from this effect. It is believed that British brewers used this term because adding hops to a finished beer led to the beer drying out further. That’s what got me thinking of Winsor.
I think it may be hops with seeds have more diastatic power and British hops often have seeds.
I have heard conflicting statement about the ability of yeast to consume oxygen post-fermentation. The issue for me is oxygen exposure at bottling time. After a cold crash most of the yeast has dropped out but there is still enough to carbonate the beer once the priming sugar has been added. That seems to me to be an indication that there is an adequate supply of healthy yeast left, but I have read several places that the yeast may be healthy enough to carbonate the beer but aren’t healthy enough to consume any dissolved oxygen so some fresh dried yeast should be added at bottling time. That doesn’t really make any sense to me.
What are your thoughts, Mark? You seem to indicate that any yeast that can carbonate can consume oxygen, which makes sense to me.
I think it is worth experimenting with.
The main problem with dry hopping and introducing O2 IME is diacetyl or drop off in hop aroma. While I do agree with some others that it doesn’t always happen it happens enough to be concerned about it. The “diacetyl” part of the equation could also be attributed to “hop creep”.
Yeast cells always consume O2 post fermentation if the ethanol level is not high enough to kills the cells off. The main benefit that bottle conditioning brings is that it gives quiescent yeast cells a new carbon source to consume, so they effectively go through a second fermentation cycle, eliminating any O2 pickup. Now, adding O2 to finished beer that contains viable cells and no carbon source other than ethanol results in the yeast cells under a diauxic shift where they can consume ethanol aerobically, reducing ethanol to its precursors (Google “yeast diauxic shift ethanol”). The effect is usually minuscule on carefully handed beer, but the threat from using a secondary fermenter to dry hop has become way overblown amateur brewer dogma. Adding a small amount of priming sugar in a 1 to 2% boiled solution to a secondary or keg will pretty much end the discussion on O2 pickup because it will eliminate diauxic shift to using ethanol as a carbon source while the yeast cells are scrubbing O2. As a community, we need to reference science before creating dogma. We are creating brewing dogma faster than it can be dispelled. I recommend reading my blog entries entitled “Carbon Credits” (Carbon Credits | Experimental Brewing) and “Have You Seen Ester?” (Have You Seen Ester? | Experimental Brewing) to anyone who wants to understand how yeast cells consume carbon and produce metabolic byproducts.