Quick Launch

Access denied. You do not have permission to perform this action or access this resource.

Master Brewers Association of the Americas > BREWING RESOURCES > Ask the Brewmaster > Posts > Calibrating DO meters
August 18
Calibrating DO meters

Q: ​How important is the BBT ppb readings on the D.O. sensors? I have been using 99.999% nitrogen which was given to me by Hamilton to zero the sensors. When I look at the specs of the gas, it says that it can have < than 2ppm o2. I am not sure that is good enough if we are trying to zero and read ppb? Even the 99.9999% can still have .5ppm O2? I have a hard time understanding the correlation of O2 in nitrogen (ppm) and O2 in beer (ppb). Is there a calculation I can use to prove this out? Also the “0” calibration and the span “210000ppm 0r 21% O2”  seems like a huge span to then try and read accurately in the ppb range. If I could find it, I would love to get a “standard” D.O in solution of 25ppb to verify calibration.

A: Extremely important - decreasing DO in the BBT is absolutely necessary to produce the best possible beer. Most DO meters for this application are accurate to about +/-1 ppb.

For both gas phase and liquid phase (DO), the O2 content can be expressed in the unit ppm (which is very confusing). However, the unit for gas is ppm vol/vol and the unit for liquid (DO) ppm m/m, so these are completely different units. As rule of the thumb, the conversion of ppm vol/vol and ppm m/m is 20,000:1

Taking your specification of the class 5.0 nitrogen with a purity of 99.999% which still can have < 2ppm O2. These are 2 ppm vol/vol and equals 2/20,000 is 0,0001 ppm m/m = 0,1 ppb m/m DO. This gas is perfectly suited for performing a zero point calibration/verification. There are procedures for creating "liquid zero" standards, but this is less accurate than using the gas standard that you already have.

It may be challenging to create or purchase a 25ppb liquid standard. An option could be requesting a certified (or even better) accredited gas mixture of N2 with an O2 content of 50 ppm vol/vol which equals approx. 25ppb m/m DO (check its availability). During the O2 verification it's important that the gas and O2 meter have a very similar temperature and the gas flow is low, so you do not have pressure build up in the O2 meter.

If you want a more practical, lo-tech opton, many breweries keep an aged beer standard of known DO in house to use as a quick, rough calibration check.

Many thanks to Frank Verkoelen and Jeff Tocio (Pentair Haffmans), as well as Kevin Sudderth (Hach) for their invaluable contributions to this response.

Access denied. You do not have permission to perform this action or access this resource.

HOME | CONTACT | JOIN / RENEW | ADVERTISE | STORE

© Copyright Master Brewers Association of Americas