GHBWNY
Well-Known Member
I've been wondering for months why two recent back-to-back brews ended up (and still do) taste fusel-y. The general consensus on here is too warm a ferm temp. While that would have been my guess, too, it was definitely not the case with either of these two. I read an article this week called, "The Biochemistry of Yeast: Debunking the Myth of Yeast Respiration and Putting Oxygen in Its Proper Place", by Tracy Aquilla (@MoreBeer website) that gave me new food for thought, especially this:
"Another thing to remember is that the oxygen 'requirement' (that is, the aeration needs) of brewers yeast is strain-dependent and that what might be adequate for one strain could be insufficient or excessive for another. For this reason, it is probably best to be familiar with your yeast, to know when aeration is necessary, and to aerate the wort only to saturation (about 8 ppm of oxygen for most worts) upon pitching and then to stop. Keep in mind also that oxygen is beneficial even at levels well below saturation, so aerating even a little will actually help a lot."
Plus... "In certain styles of beer in which metabolic byproducts of yeast growth (such as VDKs, oxo-acids, fusel alcohols, and their derivative esters) are undesirable, it is even preferable not to aerate the cold wort. Avoiding aeration may be particularly desirable when fermenting high-gravity worts that will naturally result in the formation of more esters."
It's interesting that I decided with these two beers to really, REALLY aerate them. While I don't have a way to measure ppm O2, I wouldn't have thought it possible to over-aerate via my "rock-n-slosh-on-the lap-for 2 minutes" method (had always heard you cannot over-aerate by hand, and that you should try for a 2-inch layer of foam on top). But could I have? At least for those styles? Is there a chart that recommends ppm O2-per-style?
I'm going to recommend to myself not to aerate as vigorously with the next batch and see what happens.
"Another thing to remember is that the oxygen 'requirement' (that is, the aeration needs) of brewers yeast is strain-dependent and that what might be adequate for one strain could be insufficient or excessive for another. For this reason, it is probably best to be familiar with your yeast, to know when aeration is necessary, and to aerate the wort only to saturation (about 8 ppm of oxygen for most worts) upon pitching and then to stop. Keep in mind also that oxygen is beneficial even at levels well below saturation, so aerating even a little will actually help a lot."
Plus... "In certain styles of beer in which metabolic byproducts of yeast growth (such as VDKs, oxo-acids, fusel alcohols, and their derivative esters) are undesirable, it is even preferable not to aerate the cold wort. Avoiding aeration may be particularly desirable when fermenting high-gravity worts that will naturally result in the formation of more esters."
It's interesting that I decided with these two beers to really, REALLY aerate them. While I don't have a way to measure ppm O2, I wouldn't have thought it possible to over-aerate via my "rock-n-slosh-on-the lap-for 2 minutes" method (had always heard you cannot over-aerate by hand, and that you should try for a 2-inch layer of foam on top). But could I have? At least for those styles? Is there a chart that recommends ppm O2-per-style?
I'm going to recommend to myself not to aerate as vigorously with the next batch and see what happens.