Low Oxygen Brewing

It's called a thin decoction. It's a thing. And it is a type of step mash, as is a thick decoction.

 

Yes, more of this approach vs a thick decoction. Not exactly same, I know... For some reason I misread the post and thought a thinner decoction was desired. My bad!

 

I think they use the pump for convenience and keeping the wort hot.I would assume if your boiling the decoction your're deaerating so pouring it back hot should be ok. If this was a problem then lautering would be a issue.

 

Boiling the thin part is usually the last step. You are denaturing the enzymes if you do this. The fist steps boil the thick part which explodes starch making it more available to the enzymes once the non boiled liquid is introduced. Maillard reactions also occur.

The next time I'm in a big brewery I might ask to see the mash transfer pumps that move the mash from the mash tun to the lauter tun.

 

As a pro, I add O2 inline to the fermenter as that's how the brewery is plumbed. In that case, O2 necessarily comes before pitching. At home, I pitch a half cup of low generation yeast into the carboy first. When full, I use a .5 micron stone at the lowest pressure, put it in the center of the carboy and don't move it for five minutes until shut-off. According to my scale, weighing my 02 tank afterwards, I'm using 3.5 grams O2 in 5 minutes at trickle feed and am yielding optimal efficiency and results. Oddly, the tank says 40 grams on the label, but the scale always shows 70 grams in a full tank, not just 40. That's 20 batches or 50 cents per batch per $10 bottle, which seems a small price to pay for oxygenation at such a high degree of purity, especially for those who like to repitch multiple times. I'll go pure 02 over mixing-in airborne contaminants every time.

 

@gold_strong-ales_worldcup
Great idea to weigh the O2 tank. I’ve always thought of oxygenation as pretty inexact but this approach to put some numbers on it had always been in reach. Just never occurred to me.

 

Sierra Nevada uses sterile filtered air for their ales. Sometimes I use an aquarium pump with an inline hepa filter.

 

Same here.
According to several online sources, air by volume is ~78% nitrogen, ~21% oxygen, ~ 1% argon and considerably lesser amounts of CO2 and other gasses.
I wonder how the makeup of air affects our "oxygenation", and whether suggestions to aerate as we do via a pump and stone method for XX seconds accounts for air being only 21% oxygen?

 

Using an air pump and a stone will get you up to about 8 ppm Oxygen in room temp wort and no more. And it will hold the oxygen pretty well too.

Using a bottle of pure Oxygen and a stone allows for much more saturation, up to 20 ppm or more of Oxygen in solution. I have seen the meter get above that number too though it's just wasting expensive bottled gas.

The thing is however, even if you can saturate the wort to 20 ppm, it doesn't mean it's better. How much oxygen is enough and how much is too much is another discussion.
Importantly the dissolved Oxygen falls off pretty rapidly anyway, and will settle down to around 12 ppm when using a bottle.

Cheers.

 

I always wondered this myself. At room temp, isn't the O2 coming out of solution rather quickly? I also wonder about headspace. Can yeast utlize O2 simply in the headspace? We always talk about yeast scrubbing O2 from bottles - obviously that's a much smaller area - but would that work the same way for fermentor headspace?

 

The solubility of oxygen in the wort is a function of the partial pressure of oxygen in the head space. So the more oxygen is in there (vs. other gases), the less oxygen should come out of solution. To put it another way, an equilibrium should form that balances the oxygen leaving the wort into the headspace and the oxygen going in the other direction. As the yeast consume oxygen, they should disrupt that equilibrium and draw more oxygen down into the wort. However, once the yeast start producing significant amounts of carbon dioxide, the partial pressure of oxygen in the head space should fall dramatically as CO2 enters the headspace and a mix of oxygen and CO2 exits via the airlock.

 

There it is, that's the bit I was trying to visualize in my mind. I mostly get the science around pressure equilibrium and such after years of kegging and cold crashing, I was just missing that part in my mind. That the O2 in the headspace can actually be drawn into the wort. Make sense, thanks. I assumed some of it got utilized in some fashion.

At the same time, it would also be reaching an equilibrium with pressure outside the fermentor (unless it was sealed), so O2 coming out of solution would also potentially seep right out the airlock even before fermentation starts going, no?

 

Yes, but the rate of gas exchange is also a function of the surface area, and the surface area of the liquid in the airlock is miniscule, especially compared to the large interface between the wort and the headspace. I think of it kind of like "the dose makes the poison"—if a rate is slow enough, you can basically treat it as zero. Hawaii is inexorably sinking beneath the waves (perhaps to be replaced by new volcanic islands, which in turn will meet their fate), but it is happening on a timescale that can be safely ignored for vacation planning purposes.

[Edited to add... I kind of went off on a tangent about long-term aging. For the, like, 12-24 hours during which the yeast is growing but not producing much CO2, you would lose a negligible amount of oxygen through gas exchange in the airlock. Same concept as what I described, but I focused on longer-term concerns.]

So yeah, very slowly the gas in the headspace should approach the balance of gases in the atmosphere (the airlock fluid should be absorbing CO2 from the headspace and releasing it into the atmosphere, and absorbing O2 from the atmosphere and releasing it into the headspace). But I can't emphasize enough how slow this process is. This summer I aged a sour beer for about 8 months in a Fermonster plastic fermenter with about 1.5 gallons of headspace, under a vodka-filled airlock (which I kept topped up pretty assiduously). I recently started drinking the beer, and I think there's a hint of acetic character, indicating some oxygen exposure. (This was not undesired.) But I'm quite certain that if I left a glass out overnight, the beer would change a lot from the new oxygen exposure. In other words, even after 8 months of equlibrating toward atmospheric conditions, the headspace was still very protective of the beer. (There was also a pellicle, but I doubt it was very important. Maybe more importantly, there was definitely Brettanomyces in the beer, which may have helped scavenge oxygen. Still, the point mostly stands.)

So for a clean beer, where it might sit under the airlock for 2-4 weeks, the oxygen ingress is pretty minimal.

[Edited for emphasis.]

 

An easy way to visualize pressure equalization of gas in liquid and atmosphere is to consider an open bottle of beer or soda.

CO2 molecules will leave the liquid until the pressure in atmosphere is equilibrated. That is, the beer will go flat, because the dissolved CO2 that we forced into the liquid is much greater than the gas pressure in atmosphere. And conversely, Oxygen will be absorbed until the pressure in atmosphere is equal to the amount of Oxygen in the liquid.

I use this explanation many times describingto clients how a CO2 regulator works to keep a keg carbonated. It's not really a hard concept if it is visualized.