There’s a common TPO mistake that I want to help everyone avoid. Just at about the time most people really start to understand the concept of TPO, they measure the dissolved oxygen in the package and think they are done. Let’s review the three different types of O2 measurements in packages and define each one in detail.
Dissolved oxygen is the amount of O2 dissolved in the beer at the time it is measured. It does not include any of the headspace oxygen and may or may not be at equilibrium with the headspace at the time it is measured. (If you’ve done a good job of shaking the package, then it will be at equilibrium.) If the package is unshaken, then the dissolved oxygen is equivalent to the oxygen in the beer entering the filler, plus any oxygen pickup before the fill bowl.
Filler Oxygen Pickup = Unshaken dO2 – dO2 just before the filler
Equilibrated Dissolved Oxygen
Equilibrated dO2 is the dO2 in a package after shaking, as discussed in a previous post. There is nothing special about this except that it is a common assumption that the Equilibrated dO2 is the TPO. This is not the case: equilibrated dO2 simply means that the headspace and liquid gases are at equilibrium and can be used in Z Factor type equations to calculate the TPO.
Total Package Oxygen
TPO is the total package oxygen calculated from a shaken dissolved oxygen concentration. It accounts for all of the oxygen in the package.
TPO = bright beer tank or aging vessel dO2 + filler pick-up + headspace pickup
My final thought today is that if you can keep this all straight, you will intuitively understand how to use all of the different dO2 measurements to improve your process. I was visiting a brewer a few weeks ago and he mentioned how they had picked up low but elevated amounts of dO2 between his centrifuge and his package. He said that he first noticed the problem by measuring unshaken packages. He then went looking for his trouble spot and found an easy solution: now that beats rebuilding a filler!