I want to know more about the legitimacy of this thought...
I have read all over that infusion of pure O2 in cooled, post-boil wort, is the best means of generating a strong fermentation.
I wonder why it isn't just as beneficial to simply use filtered air via pump, filter, and air stone? (I know this works, but some people I've talked to frown upon it.)
I know that it would take longer to aerate wort with this method.
I wonder this because air, obviously, contains (roughly) 21% O2 and 79% N2 (ignoring other trace gases).
But won't the N2 also dissolve into the wort and provide a valuble food source for yeast?
If so, why wouldn't this be more beneficial to use than O2? (Bearing if one has an extra 20-25 minutes to use this method)
Oxygenating wort is to help yeast propagation - the little critters need it to create sterols, which are the lipids they use to create cell membranes (ie MORE yeast ).
As far as I'm aware, it's more the commercial people who like to use O2 - and it's just like you said; 'cause it's faster. There's also the added advantage of knowing the general dissolution rate of the O2 so you can calculate an approximate amount of O2 added, whereas the content in air can vary a bit.
Air, IMO, is actually better, 'cause it's super easy when using pure O2 to actually OVER oxygenate your wort. I know several commercial brewers who use air instead, and several more who don't even bother to 'aerate' (it splashes into the fermenter, and they're happy with that).
Not sure about the N2 dissolution, but if it does go into the wort I think it's in the wrong form for yeast nutrient. It CAN, however, give you a creamier head (think guiness widget). Hope that helps!
Nitrogen compounds are fine nutrients for yeast, but N2 isn't really a useful form, being way too inert. The only common processes that can make it into a nutrient are lightning and other electrical phenomena, or else certain types of nitrogen-fixing bacteria. Hopefully neither of these will be in your wort.
The only reason I can imagine a brewpub not worrying about O2 is that they pitch a massive slurry and don't need to promote yeast reproduction. It would be the same for homebrewing scale to pitch on the cake. However, if you're starting from a fresh pack of yeast like a white labs vial or propagator pack, you really do need to oxygenate the best you can. Why not use a pump? Because it takes about 30 minutes and you still can't acheive optimum dissolved oxygen.
Pure oxygen injection can acheive optimum DO in 60 seconds, it's quick and completely sterile.
But won't the N2 also dissolve into the wort and provide a valuble food source for yeast?
Very few critters can deal with N2, gaseous or dissolved. Every plant on the planet is dependent on a few types of bacteria and lightening.
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Gasses transfer from atmosphere to the wort along any surface area. Stirring creates more surface area and also gets the wort to turn over so more of the volume reaches the surface to take up O2. Sending bubbles also turns the wort volume over, and also adds surface area because each little bubble rising up has a little surface area on it's own. Stands to reason if those little bubbles hold pure O2, then more O2 will get in during the time that bubble takes to make it to the surface and pop. Add a higher concentration of O2 in the headspace of your fermenter during your aeration time and that makes oxygenation that much faster.
That said. I splash and stir and call it good.
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Nitrogen compounds are fine nutrients for yeast, but N2 isn't really a useful form, being way too inert. The only common processes that can make it into a nutrient are lightning and other electrical phenomena, or else certain types of nitrogen-fixing bacteria. Hopefully neither of these will be in your wort.
yep, on the money with this. Atmospheric nitrogen must first be converted to a usable form of nitrogen otherwise it's not going to react.
I've seen it written or implied that the maximum O2 concentration possible with "air" aeration is around 8ppm, which is pretty good... especially with the right size starter. Injecting pure O2 can get the concentration higher than with plain air.
Also, I believe the dissolved O2 in any wort/beer is either used up by the yeast or off-gassed in like 8-12 hours anyway.
As far as the N2 goes, even if it did combine with other compounds to form yeast nutrients, it's probably negligible compared to the amount of nutrients already in the wort... particularly from an all grain brew.
In general, it is difficult for homebrewers to achieve sufficient oxygen levels. The levels of oxygen necessary for optimal fermentation vary depending on the yeast strain. Ale strains usually need between 8-12 part per million (ppm) while lager strains require slightly higher amounts (10-15 ppm). At atmospheric pressure the maximum level of dissolved oxygen in wort is approximately 8 ppm and the saturation level decreases further as the gravity of the wort increases. Thus unless special steps are taken to introduce air or oxygen into the wort, it is difficult for homebrewers to achieve adequate aeration. Recent studies have shown that oxygenation is by far more efficient than aeration. Injection of oxygen through a 2 micron diffusing stone can actually supersaturate the wort with 10-12 ppm of dissolved oxygen being reached in 5 gallons of wort by a single 60 second blast of oxygen!
Thus unless special steps are taken to introduce air or oxygen into the wort, it is difficult for homebrewers to achieve adequate aeration.
When they say 'adequate aeration'...isn't that dependant on pitch rate? It seems if you pitch enough yeast that NO aeration would be 'adequate'.
I have a question about pure O2 and contamination. Below are some links to an experiment that was done in which a bunch of people brewed the exact same recipe but used whatever equipment/process they typically use. If you look at the results table it summarizes the results and the brewers that used pure O2 fared extremely poorly wrt infections. The pure O2 injected beers appeared to have a trend but it's a very small sample size. Still...seems enough to be a concern for those considering going the pure O2 route (like me...right now I just splash it around inside the carboy and my ales always finish at or very near the limit of attenuation per my fast-ferment tests).
Any guesses why the pure O2 injected beers fared so poorly regarding infection? Perhaps putting all that O2 in there exacerbates any poor sanitation problems?
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Last edited by SpanishCastleAle; 06-09-2009 at 03:38 PM.
Using air instead of O2...
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