This is the first of a two-part post on caustic “air” measurements. We’ll start with a brief historical glimpse at air testing and then talk about both the upside and the limitations of this type of testing.
In 1989 I worked with a team that wanted to quantify the amount of dissolved oxygen in beer. We purchased a Zahm-Nagel “air tester” to see how it compared to using a dissolved O2 analyzer on shaken packages, where the values we obtained were then used to calculate total package oxygen. (An air tester looks at all the gasses in a package that are not CO2.)
The idea was to simply try and correlate “air” to Total Package Oxygen (TPO.) Sometimes the air-to-TPO values were fairly predictable and repeatable, but other times the air readings differed greatly from our expectations. Because of this, and because we knew that TPO was giving us accurate results, we stuck with it and dropped further air testing, but we never really got to the root of the discrepancy.
When I did that air-to-TPO comparison, I used a method in a 1980s edition of the American Society of Brewing Chemists (ASBC) Methods of Analysis (MOA). As I did the research for this post I wanted to look back at that old method, but it had been archived by the ASBC and was no longer available. So I called the Zahm-Nagel Company (they still make air testers) and spoke to a very kind gentleman named Loren, who graciously found “Beer 15” in a 1949 copy of the ASBC MOA. The procedure was apparently adopted in 1946, based on the work of an ASBC subcommittee between 1944 and 1945.
What can an “air” measurement tell you? If you’re sure that excess O2 in a package is an air-in-the-headspace issue, then a simple air measurement may be all you need. But if the issue is dissolved oxygen, then it may not be your best bet. The next part of this story is a practical example of the difference between air and TPO measuring in a troubleshooting situation.
I was in a Latin American country a dozen years back, helping root out the source of occasional high TPO measurements. The brewers were convinced that the undesirable results were the fault of the dissolved oxygen analyzer, but I couldn’t find anything wrong with the instrument. I proposed that we pull multiple bottles off single-filler valves and look at both the TPO and “air content” of the packages. Since it was easy to do, we grabbed ten samples from each of three specific filler valves, and ten samples randomly from multiple filler valves. Below is a table with our results.
|Location||# of Samples||Total Package O2||“Air”
|Random||10||83 ± 32 ppb||0.25 cc|
|Valve A||10||102 ± 106 ppb||0.25 cc|
|Valve B||10||799 ± 205 ppb||0.35 cc|
|Valve C||10||84 ± 26 ppb||0.25 cc|
As you can see, the TPO data from one valve showed a distinct deviation from the other valves. The “air” reading from the bad valve also showed a slight increase compared to the other valves, but it was not as large as the TPO rise, and did not reflect the extreme discrepancy between valves. By looking at a few shaken vs. unshaken measurements, we were able to confirm that a faulty seal on the filler head was failing to pull adequate vacuum on the bottles. This data was more confirmation that air results might not correlate very well with TPO, but I never really examined why until a few years later. We’ll talk about that in part two of this post.
For now, this is my final thought: caustic air measurement is a time-tested tool and there may be circumstances when it’s all you need, but if you are having flavor issues due oxidation then TPO will always be a stronger diagnostic tool.