oxygen for yeast growth

[damoller]

Hi, I was wondering if anyone had a formula for converting ppm O2 levels to liters O2 gas per barrel? Thank you very much!

[dick murton]

32 grammes O2 occupies 22.4 litres at STP, i.e. zero deg C, and one atmosphere pressure.

(P1 * V1) / T1 = (P2 * V2) / T2

Where P = pressure in atmospheres, V = volume, T = Temperature in Degrees Absolute = deg C + 273.

Crudely, this means for example, if you double the pressure, you double the mass of gas in a given volume, or for a given mass, you halve the volume, providing the temperature stays constant.

Not being used to American barrels, I don't know how many litres there are in a barrel. But at least you now have the basics

Cheers

[damoller]

I once set up a spread sheet for this but between windows crashes I have lost it and could not find my referance to the equation.

[tlenahan]

This list below shows the relationship between Oxygen and liters of O2. Besides the calculation there is a limit to the level of oxygen that can be absorbed by the beer, about 11ppm. It is a function of temperature and atmospheric pressure. This assumes your filling and maintaining your fermentor at atmospheric pressure. This equation also factors in 25% efficiency for injection loss. The equation is:

X ppm O2/1000000 x beer BBL x 8.3 x 453 x 26.62/1000/.035315/25%


ppm bbl liters
O2 beer O2

5 1 1.76
6 1 2.11
7 1 2.46
8 1 2.81
9 1 3.16
10 1 3.51
11 1 3.87

I can provide you with a spreadsheet for this calculation taking into consideration operating variables if desired. Please call Tim Lenahan (303)431-9168 or e-mail timlenahan@msn.com

[MikeJordan]

There is a limit of Oxygen absorption but it varies depending if you're using pure medical grade O2 or filtered air. Which are you using? It is very easy to over oxygenate your wort stream with pure O2.

[dick murton]

The limit for solution of oxygen in wort when the source of the oxygen is closer to 8 ppm. If using pure oxygen I am told you can get near to 32 ppm, though the most I have ever used is 22 ppm. I suspect that this would only be achievable if the temperature was down to zero deg C, so not a realistic option for brewing.

However at these levels we found if you need to get such high levels for yeast to ferment properly (very strong worts) you were actually better off aerating the wort for a time shortly after pitching, once the yeast had mopped up the oxygen dissolved on the way to FV

Cheers

[tlenahan]

Under barometric conditions there is no way you can get beyond 11 ppm of oxygen in wort at the typical fermenting temperatures used. Possibly as the oxygen is injected there maybe higher levels of oxygen, but the oxygen will come out of solution unless the wort is under pressure. The solubility also drops as the gravity of the wort goes up, so it is pretty hard to get above 8ppm even by injecting with pure oxygen. More typically you should expect to see about 5-8ppm oxygen in the wort as being saturated at barometric pressure. Also those brewing at higher elevations will have lower levels of oxygen saturation as well.

[tlenahan]

Under barometric conditions there is no way you can get beyond 11 ppm of oxygen in wort at the typical fermenting temperatures used. Possibly as the oxygen is injected there maybe higher levels of oxygen, but the oxygen will come out of solution unless the wort is under pressure. The solubility also drops as the gravity of the wort goes up, so it is pretty hard to get above 8ppm even by injecting with pure oxygen. More typically you should expect to see about 5-8ppm oxygen in the wort as being saturated at barometric pressure. Also those brewing at higher elevations will have lower levels of oxygen saturation as well.

[MikeJordan]

I wish this were the case so brewers didn't have to spend extra money for in-line DO meters on their wortway. Generally only 8-10 ppm of DO is needed for sufficient yeast growth and alcohol production. The problem is you can over oxygenate your wort and cause your yeast to grow excessively and not produce enough alcohol. This is great if you're growing yeast but not so good when trying to make beer. The fermentation can be too vigorous and the beer flavor and ester formation will be off. I have seen very high DO levels (24 ppm) using Orbisphere inline meters and agree that some of it will come out of solution when filling a fermenter. The problem is you can flash the fermenter enough to get foam out the blow off line (especially on mutli-fill tanks). If this isn't the case then you have to assume the yeast is already mopping the O2 up as it has been reported that this can occur within 3 hours for some yeast strains. All this can really be if concern if using pure O2 as it has also been reported levels of 50-60 ppm DO are attainable. Personally I would rather aerate on the high side but I think it's too easy to overshoot especially when using pure O2. Usually comes down to trial and error if you don't have a DO meter.

[tlenahan]

I would agree that over oxygenating wort is possible, and most probably people injecting pure oxygen should establish emperical control into their fermenting operations checking yeast growth rate, cell viability, attenuation rate, and flavor oxidation especially with multi fill brew fermentors. I guess I have seen too many cases where people have under pitched or underaerated the wort.

The original question had to do with establishing the quantity of Oxygen lters vs ppm. Using an inline DO meter to control oxygen injection is the logical approach to prevent both types of problems from occuring. Without a DO meter a brewer can still oversee fermentation, yeast performance and beer flavor. I've used oxygen injection and did not run into problems.

[damoller]

Hi everybody, THanks for the help.
I am also looking to get a O2 meter and was needing help on how to mount the sensor probe through a TC fitting(1.5"). Can any one help, for that matter I need to mount a pH probe through a TC fitting also.

[T-breds]

O2 meter trials (years ago at Old Dominion) largely reflected Mike's. Further, we found that over oxygenation of ales could lead to excessive diacetyl production, which would not be fully taken up at the end of fermentation. There is some old literature to support this theory, but it doesn't seem to be a concern to most brewers. It might be a good subject for further experimentation. (Note: in our experience, lagers were not prone to the higher diacetyl production with higher O2 levels).

Dean