Wort oxygenation equation?

[dustinstriplin]

Hi, I'm looking for an equation I can use to estimate approximately how much dissolved oxygen I have in my wort. I haven't seen any useful scientific data around predicting ppm of dissolved oxygen in wort. The best info I've found was a table that showed the ppm after x amount of time, but it doesn't include the variables present when calculating the table, so it's not very useful.

I'm using pure O2, with a known flow rate, and a known hole size on my air-stone. I am dissolving into carboys by dropping the air-stone in.

 

[Gnomebrewer]

Try asking in the brew science forum.
I could come up with a formula based on the mass of Oxygen given the flow rate and the volume of beer, which would assume no loss of O2 from the surface of the beer (it's simpler with in-line oxygenation), but it could be overlooking something. There's bound to be someone on the Brew Science forum that knows a bit more about it though.

 

[Gnomebrewer]

My method (which may or may not be correct):
O2 has a mass of 1.43g/L = 1430mg/L at STP
f = flow rate (in L/second)
v = volume of beer/wort (Liters)
t = time (seconds)
x = oxygen content of wort (in mg/L or ppm)

x = 1430f * t / v

Again, this assumes no loss of oxygen, which is unlikely.

 

[Robert65]

I'm sure this could be done, but I have to ask: If you have a SOP and it's yielding good results in fermentation performance, why do you need to know any more? The ability to achieve consistent, repeatable results is what is important in practical terms. I too use pure O2, know my pore size (2 micron) and flow rate (0.2 L/min.) and my wort volume and density (also important factors in determining achievable DO level) are always within a fairly narrow range. I vary the time somewhat if wort density is higher or lower, and experience shows that my procedure works. That's what I need to know.

 

[petemoss]

I've been messing around with this myself, trying to come up with the time in seconds at a certain flow rate to hit a specific O2 saturation. I actually started out working my calculations based on mass alone. This entailed coming up with the grams of a V sized batch of wort at a certain gravity. Then going for how many grams of O2 were needed per million grams of wort. This was before I ran across that ppm are apparently standardized on mg/L. After changing my formulas around the results were actually very close to each other.

The part that concerns me is that, unless I am doing something way wrong, the times in seconds seem really short. For example, for 5 gallons of wort and shooting for 12 ppm at 1L/min, I get around a 10 second flow time. All of the literature I have read says that to properly oxygenate wort at 1L/min should take about 1 min. Maybe this is the difference between theoretical vs real life with O2 losses. I'm not sure. It just leads me to feel that calculating it may not work in real life, and as @Robert65 has said, I should stick with what works.

 

[day_trippr]

There are so many variables that can affect O2 absorption in our application it'd be a hella complex equation to even ballpark the result. O2 flow rate, airstone pore size, temperature of the wort, gravity of the wort, depth of the wort, whether the wort is still or in motion (eg: "swirling" with a wand), and on and on.

About all one can do short of investing in an O2 meter is to use the data others have generated. There was a fellow on HBT years ago that drew up a graph of some examples he'd tested, and then there's Chris White's empirical data in Yeast, both led me to using .5 lpm for four minutes for the typical 5.5 gallons in the fermentor...

Cheers!

 

[petemoss]

Thank you @day_trippr. I realize that I am in way over my head, unless a yeastwortoxyoligst want's to jump in here with the definitively correct formula. I guess moving forward I will just use the empirical data, not even mine at that. I know that my last batch I did a 1 liter/minute and it kicked off like a rocket. I may try the 1/2 for four though just to see what happens.

 

[dustinstriplin]

Darn, I was hoping there was something out there. Thanks for the responses all!

I just rechecked Chris White and Jamil Zainasheff's book, "Yeast", and found a useful table. They left a lot of room to expand on the subject, but it is some of the best info I've seen so far. The table gives the flow rate (1L/min), wort volume(20L), OG (1.077), and air stone hole size(0.5 micron). Based on their table, oxygenating for 30 seconds resulted in 5.12 ppm, 60 seconds was 9.20 ppm, and 120 seconds resulted in 14.08 ppm. As one would expect, there are diminishing returns for keeping the O2 on longer. The table doesn't go into different OGs, temperatures, or volumes, which would have been cool. This does seem like a solvable problem, but the devil is in the details. If I ever get my hands on an O2 meter then I'll be sure to run some experiments.

I hope I find the HBT graphs you're talking about day_tripper, that sounds like an interesting post. What dissolved O2 ppm are you targeting by oxygenating @ 0.5 L/min for 4 mins?

 

[day_trippr]

I took White's 1 ppm for two minutes and cut the rate in half and doubled the duration, so should be in that same 14ppm ballpark...

Cheers!

 

[TallDan]

I use this as a guide:
https://www.homebrewtalk.com/forum/threads/all-you-ever-wanted-to-know-about-oxygenation.414616/

 

[Qhrumphf]

If you really want to know, Milwaukee sells a DO meter that should be plenty accurate for wort oxygenation (but not for cold side after that point...).

But as others have said, if your process is consistent, and results consistent and the way you want them, then why does it really matter?

 

[dustinstriplin]

I use this as a guide:
https://www.homebrewtalk.com/forum/threads/all-you-ever-wanted-to-know-about-oxygenation.414616/

Thanks, this was a good read.

 

[dustinstriplin]

If you really want to know, Milwaukee sells a DO meter that should be plenty accurate for wort oxygenation (but not for cold side after that point...).

But as others have said, if your process is consistent, and results consistent and the way you want them, then why does it really matter?

Yea, maybe some day I’ll get one. I just thought there was a chance someone has already done the research.

I’m looking into this because my results have not been consistent on high OG beers. Even if I was happy with my results, I always want to improve. I have seen plenty of reports claiming that better beer is made when O2 levels are optimized.

 

[petemoss]

So, based on the variations of formulas and general emperical data, it seems like there is a fairly wide range of possible "right" answers to flow rates needed for proper oxygenation. Short of using a DO meter we may never know for sure.

I have heard that over oxygenating can be bad. Do we think that our range of oxygenations that we could actually lead us into a problem, or is that not really an issue in real life?

 

[Robert65]

We know it's impossible to over oxygenate with air, but all that foam by the time you reach saturation at 8pm means less foam on beer. We can probably over oxygnenate with pure O2, if we're really good at not letting bubbles break the surface, but at least with less impact on foam. Some have experimented with things like hydrogen peroxide, and definitely overoxygenated. It's a balancing act. I think the bottom line is that healthy yeast in good wort don't need nearly as much O2 as we might think, so restrained pure O2 is the best middle ground. And again, let the results determine empirically what works in your own brewery. My take.

 

[petemoss]

Thanks @Robert65, speaking for myself, I think that is how I am going to proceed.

 

[Robert65]

Yeah, the original quest was to have something like this: when I did P, I got X ppm, and A result; when I did Q, I got Y ppm, and B result. Why not cut out the middle term? Correlate procedure with result.

 

[petemoss]

Good point.

 

[dustinstriplin]

I think the bottom line is that healthy yeast in good wort don't need nearly as much O2 as we might think, so restrained pure O2 is the best middle ground. And again, let the results determine empirically what works in your own brewery. My take.

I don't know what "restrained pure O2" means. Obviously, we don't want to over-oxygenate. We don't want to under-oxygenate either. I'd prefer to keep my O2 levels in the generally accepted optimal range for the wort's gravity. As brewers, we taste the results and determine if it works for us or not. I strive to control as many variables as I can. I believe this gives me greater control over the results, enabling me to tune my process efficiently. I also enjoy the chemistry aspect.

Based on Chris and Jamil's chapter on fermentation, O2 concentration has a very significant impact on attenuation. Wort that is oxygenated to the recommended range (9ppm) for 1.05 OG, finished attenuating faster than under-oxygenated wort (5ppm). It also finished attenuating lower. There is no doubt that a healthy pitch of the correct cell count for the OG and style is an important factor in producing good beer. Given the evidence, I don't think the optimal O2 ranges can be discounted so easily.

It seems like we have some decent answers to help predict the O2 concentration, which was the goal of this thread. Perhaps one day I'll get a O2 meter and put the equations to the test. If anyone does this first, then I look forward to reading about it.

 

[Vale71]

I don't know what "restrained pure O2" means.

I think it's a more elegant way of saying "I'm just eyeballing it".

 

[Robert65]

I think it's a more elegant way of saying "I'm just eyeballing it".

More or less, yeah. Turn it on till the bubbles just barely break the surface, and only give it a minute, maybe two for a big beer. I have a flow meter for consistency (recent addition) but it's not really necessary. Adjust timing based on experience, but there's probably no need to give it several minutes of pure O2. Consider that German brewers are restricted to use of air, and so never exceed 8ppm, yet have successful lager fermentations. In fact, Kunze (ch. 3.9) stresses the need to minimize aeration for various reasons, noth to avoid damaging wort and to avoid damaging yeast, achieving "just enough" being a delicate balancing act. For those interested, that's a very good discussion of the topic. Otherwise, err on the side of caution.

 

[dustinstriplin]

It sounds like our oxygenation regimen is almost identical. I recently had attenuation issues with a couple big beers. Up until recently, I’ve been using an air stone with an unknown hole size. I suspect oxygenation is the issue for under attenuation.

Do you have a link to the Kunze reference? Sounds like a good read.

Edit: This is the only book I can find by Kunze, is this it? https://www.amazon.com/Technology-Brewing-Malting-Wolfgang-Kunze/dp/392169034X

 

[Qhrumphf]

It sounds like our oxygenation regimen is almost identical. I recently had attenuation issues with a couple big beers. Up until recently, I’ve been using an air stone with an unknown hole size. I suspect oxygenation is the issue for under attenuation.

Do you have a link to the Kunze reference? Sounds like a good read.

https://www.carllibri.com/epages/62...th=/Shops/62355332/Products/1012&Locale=en_GB

 

[Vale71]

Consider that German brewers are restricted to use of air, and so never exceed 8ppm, yet have successful lager fermentations.

There is no such restriction in Germany. The reason nobody uses pure O2 at a commercial scale is because oxygenation is done inline right before yeast pitching, which is also performed inline. Pure O2 could thus come in contact with yeast before being completely dissolved and could damage it reducing vitality and viability.

 

[Alex4mula]

From the metrology prescriptive I wonder how accurate is your measuring equipment to ensure you are actually getting 1L/min or anything else. Unless you use an expensive calibrate equipment I wouldn't trust any of the cheap gauges sold at brew shops. I assume the actual PPM could be all over the place with those.

 

[day_trippr]

fwiw, considering I've been hooked up to an identical model regulator as this one more than once in my life...

...I'm inclined to trust it

Cheers!

 

[Robert65]

There is no such restriction in Germany. The reason nobody uses pure O2 at a commercial scale is because oxygenation is done inline right before yeast pitching, which is also performed inline. Pure O2 could thus come in contact with yeast before being completely dissolved and could damage it reducing vitality and viability.

Briggs, et al., chh. 10.11 and 14.3, just to name one source, covers the general use pure O2 (up to 20 ppm) in current practice. Also discussed are the precautions needed. So it isn't true that nobody does it. They just need to have monitoring capabilities and understanding of the needs of a specific combination of yeast and wort well beyond the scope of homebrewers, and under homebrew conditions the yeast will have far more forgiving requirements anyway.

 

[Gnomebrewer]

From the metrology prescriptive I wonder how accurate is your measuring equipment to ensure you are actually getting 1L/min or anything else. Unless you use an expensive calibrate equipment I wouldn't trust any of the cheap gauges sold at brew shops. I assume the actual PPM could be all over the place with those.

It's quite easy to calibrate.
Grab a container with volume markings on it (about 2 to 5L is good and easy to handle).
Fill the container with water to the brim. Also half fill a bucket with water.
Quickly invert the full container into the bucket trying not to spill any (hold something over the opening).
Run O2 at a set rate (say 1L/min) as read on the flow meter.
Push the end of the O2 hose into the inverted container and start a timer. O2 will displace water.
After t minutes, x volume (litres) have been displaced as measured in the container, so actual flow rate was x / t liters per minute.
Doing this a few times will also show variability in the flow meter.

I personally wouldn't bother though - just run the O2 until there's a little bit of bubbling on the surface, then back off slightly so the bubbling stops and go for 30 seconds to a minute for normal gravity ales and a bit longer for lagers and high gravity beers.

 

[Alex4mula]

I personally wouldn't bother though - just run the O2 until there's a little bit of bubbling on the surface, then back off slightly so the bubbling stops and go for 30 seconds to a minute for normal gravity ales and a bit longer for lagers and high gravity beers.

Ok. This is more or less what I do.