When using a portable dissolved oxygen analyzer to measure package oxygen concentrations, you have two options:
- Measure the package directly off the filler.
- Shake the package until the liquid and headspace gases reach equilibrium and then measure.
Let’s dive deeply into interpreting the results of unshaken packages and learn what it tells you.
Since we aren’t doing anything to the container to equilibrate the headspace gas with the dissolved gas in the liquid, an unshaken package gives us a snapshot of these three oxygen influences:
- Dissolved gas in the liquid right as it enters a filler.
- Dissolved gas pickup during filling due to air in the package that has not been cleared before the package is filled.
- Fill bowl O2 pickup in rotary fillers
The differentiation of these is easy to quantify. One is the dO2 at the base of the filler and the other is the dO2 measured in the package minus the dO2 at he base of the filler. Here’s an example:
- dO2 of an unshaken package = 63 ppb or 0.063 ppm.
- Base of filler dO2 = 18 ppb or 0.018 ppm.
- Filler dO2 pickup = 45 ppb or 0.045 ppm.
Since it is relatively easy to measure just before the filler and just after filling, let’s discuss what influences the results of each.
The dO2 concentration of beer at the base of the filler is usually easy to control and is based on just a few potential influences. High values can be caused by:
- High residual in the finished beer tank.
- Oxygen pickup from a pump between tank and filler.
- O2 pickup from a valve or fitting between tank and filler.
Likewise, if you make it a practice to regularly measure the dO2 at the base of your filler and then calculate the filler valve pickup, it can give you great feedback on when to service your filler. If the O2 at the base of the filler is low, but the unshaken dissolved O2 is high, then perhaps there are ways to alter your filler system to achieve lower values. Here are some potential areas of oxygen pickup:
- Purging on rotary bottle fillers as impacted by vacuum pumps, CO2 purge duration, fill tube lengths, filler speed, and fill bowl characteristics.
- Effectiveness of CO2 purge pressure and flow on an inline batch bottle filler.
- CO2 purge time, fill tube lengths, filler speed, and fill bowl characteristics on rotary can fillers.
- CO2 purge pressure and flow on an inline can filler.
So we can learn a lot from measuring gas content in unshaken packages, although it’s important to remember that an unshaken package won’t tell you if you’re picking up oxygen from a can-seamer or while fobbing bottles, since they can contribute to oxygen in your headspace. Total Package Oxygen (TPO) takes into account headspace oxygen and is the only calculation that can give you a complete picture of the oxygen in your finished product.
My final thought is that understanding unshaken package dO2 measurements will help you troubleshoot some sources of package oxygen contamination. Next time we’ll examine shaken package measurements and tie it all back total package oxygen.