Dissolved oxygen can increase or decrease at many points during packaging, and sometimes we see values that differ pretty wildly, depending upon where they were taken in the process and the specific parameters of the measurement.
I have a customer who was getting some odd package oxygen results and she wanted to understand if the data were real, and if so, why. Here are the numbers:
Base of Filler dO2: 110 ppb
Unshaken dO2: 93 ppb
Headspace O2: 38 ppb
Shaken dO2: 60 ppb
Total Package Oxygen: 131 ppb
Package Volume: 355 mL
Headspace Volume: 17 mL
Temperature: 9 oC
It’s unusual to see an unshaken dO2 value that’s lower than the value at the base of the filler, so that was our main focus. After establishing that this was an occasional trend for her filler, but not something she was seeing all the time, and after validating the instrumentation to be sure the readings were correct, logic dictated the rest:
1. The flow into her fill bowl was very turbulent and the beer was losing oxygen in the bowl because the O2 content of the bowl’s headspace CO2 was lower than the O2 content of her beer.
2. The shaken dO2 was lower than the unshaken dO2 due to the efficiency of the jetter. Since the package dO2 was a bit on the high side, the beer lost oxygen into the headspace during shaking.
This particular case was interesting because beer usually picks up dissolved oxygen between the base of the filler and the unshaken dO2 in the package, but every once in a while the opposite can happen. In this particular case I suggested that the flow of CO2 into the bowl might be excessive and that lowering it would probably result in a more expected set of numbers.
My final thought is that when your results don’t make sense and you know your instrumentation is working correctly, pay attention to whether it’s a trend you see repeated, or if it happens only under specific circumstances. If it happens during specific situations, then there’s usually an easy explanation.