In follow-up to my June 20th post about the difference between dissolved oxygen and TPO, I want to share a conversation I recently had with a customer about the dO2 results he was seeing on his canning line, and the way simple dO2 measurements of shaken and unshaken packages were able to help him sort out a problem.
This brewer was doing a good job of getting his beer to the filler — he reported having less than 10 ppb going into the filler — but he couldn’t understand why he was then seeing shaken package dO2 levels that were high and unpredictable. So I asked about his filler pick-up in an unshaken can. Filler pickup is equal to unshaken dO2 minus the base of the filler dO2. He said it was about 40 to 50 ppb, but his shaken dO2 ranged from 300 to 600 ppb and was sometimes higher. So where was the oxygen coming from, and why?”
I told him that the oxygen had to be coming from air trapped in the foam, then did a quick calculation to show that it really could rise that much. If all of the headspace in a 12 oz. package were air, the can or bottle would pick up between 3 to 5 ppm of oxygen, depending upon the size of the headspace: the more air that got into a particular package, the higher the shaken dO2.
Here is a quick tip to help you easily sort out if the bulk of your oxygen is in the headspace or the liquid. Since packages are not at equilibrium just after canning, the dissolved value of the container is going to either increase or decrease, depending where the majority of the oxygen is at the time the closure goes onto the package. If you measure the unshaken dO2 and then the shaken dO2 and follow these two simple rules, it will quickly lead you to the answer:
- If the dO2 of the package increases, the majority of the oxygen was in the headspace – it shifted from the headspace to the liquid upon agitation.
- If the dO2 in the package decreases, the majority of the oxygen was in the liquid – it shifted from the liquid to the headspace upon shaking.
My final thought is that a simple test like comparing the dO2 on shaken and unshaken packages can tell you a lot about where to focus your troubleshooting effort.