Without a DO meter we are all guessing as to how much oxygen has been added to our wort at the start of fermentation. Oxygen is important in the initial phase of fermentation. It is required in the production of sterols which allow for cell wall permeability. Without a sufficiently permeable cell wall sugars cannot flow freely into the yeast. This makes it difficult for the yeast to obtain the nutrients they need and will leave the yeast in poor health. The yeast will not be able to divide to the population creating the same effects as under pitch yeast. In addition the fermentation will be slow, and the yeast will be stressed which can result is stress excretions by the yeast. (1)(2)(3) All around under oxygenating is bad news.
This leads to the question of "can you have too much oxygen?" The simple answer is yes. Fix goes into detail about the repercussions in "Principles of Brew Science" (1) If you haven't read it, I highly recommend that you pick up a copy. For starters, excessive oxygenation leads to excessive cell division which leads to similar problems with over pitching.(4) Over oxygenating is a good way to get low phenol and low ester aromas and flavor out of your yeast. For a lager this might be a good thing, but for most Belgium, German, and English styles you'll want that contribution.
True saturation is never really possible, but 95%-99% should be achievable and repeatable. Some tests show that rocking and shaking can achieve this level in minutes.(5) Additionally, the saturation point could change about 5% based on other factors such as temperature, pressure, and to a small degree, wort content. The saturation point of sucrose 2000 grams per liter. (6) Compare this to a 1.100 wort (for a very big beer) that would only have about 280 grams of sugar per liter.
With air, the saturation point of oxygen is 8ppm. No matter how much you mix, pour, shake, pump air into the wort, it's not getting any higher than 8ppm. This can be used to your advantage. If you want 4ppm, or half of the saturated content, then aerate half of your wort, and the mix that with the other half that has not been aerated.
With pure oxygen the saturation point is about 50ppm. The sample principles can be applied to using pure O2. If an ale pail is purged with oxygen, and then agitated, it can be saturated to 50ppm of oxygen. This is much more oxygen than is needed for any reasonable beer.
Does anyone want to test this? Unfortunately I don't have an O2 setup, or a DO meter.
The table below shows the percentage of the wort that will need to be saturated to achieve the desired oxygen content in the wort.
ppm of oxygen required
Percentage of batch to saturate.
how many gallons to saturate for a 5 gallon batch
(1) "Principles of Brewing Science" Fix
Do you really think total saturation is achievable in practice? There seem to be conflicting reports (White Labs vs Wyeast studies).ReplyDelete
You're right that true saturation is unlikely, but I would expect that near 90% would be achievable and repeatable. The remainder of the wort would also have some oxygen in it. This is why it would be nice be able to do some experimentation with a dissolved oxygen meter. I'll see if I can clean up the verbiage to make it more clear.Delete