TPO Measurement: the Importance of Methods Validation

Total Package Oxygen (TPO) can be such a confusing topic that it’s worth an ongoing discussion. Since real-life examples are often the easiest to grasp, today we’re going to look at TPO from the perspective of a brewer who is actively trying to troubleshoot his new seamer. Even if you aren’t canning, you should be able to apply this information to problems with a bottle filler.

In this case, the Brewer has purchased a new seamer that is specifically promoted as keeping TPO low, and yet his TPO measurements after seamer installation are nowhere near as low as the seamer company says they should be. When the brewer and I talked, I was immediately struck by what the seamer people had provided as the target TPO: 20 ppb, which is super low by any standard. So our next step was to try and understand the origin of that number.

The seamer manufacturer really wasn’t able to tell our brewer why his values were not meeting expectations for the seamer. After some initial probing, it turned out that the seamer people were sincere in their beliefs about the abilities of their seamer, but they didn’t have a lot of experience with beer, and had based their numbers on data from only one other customer. Knowing this, we then formulated some questions for that customer.

We’re still waiting to hear back, but here’s what we’ve asked:

  1. What was the reading from the package when measured on their dissolved oxygen analyzer?
  2. Was the package shaken or unshaken?
  3. If the package was shaken, did they calculate the TPO from the dO2?

Here’s what the answers to each of these questions should tell us:

  • If the answer to the first question is in the range of 7 to 10 ppb, then it really is in the realm of possibility that their TPO is 20 ppb, as long at the instrument was validated (more on that in another post), the package was shaken, and they did a correct TPO calculation.
  • If the answer to the first question is 20 ppb, then we need to know if the package was shaken. If it was shaken then it was at equilibrium, but did they calculate the TPO?
  • If the package was unshaken, then the value they were calling “TPO” was actually just the dO2. This represents only the oxygen concentration of the beer coming into the filler and the pickup in the filling process. To get the TPO, they still needed to measure the dO2 on shaken packages and calculate TPO based on the dO2, package temperature and the liquid and headspace volumes.

It will be interesting to see what happens, but my guess is that the numbers provided to the seamer people – and thus to our brewer — were not TPO. They may be shaken or unshaken DO2 – both are possible.

My final thought is that when someone tells you a dissolved gas value upon which you must rely, ask how it was derived. The reliability of measurement is only as good as the validity of the method by which it was obtained.

I Know My Beer’s dO2. What’s Next?

Knowing your dissolved oxygen levels won’t help unless you have an internal standard, a dedication to monitoring, and a plan for fixing your problems. In my many years of working with brewers, I’ve found that those who set a goal and commit to that metric do the best.  So the first step in your monitoring program should always be a comprehensive picture of the amount of dO2 you are willing to tolerate at each step of the process, not just the finished product.

Let’s say the dO2 in your bright beer tank (BBT) exceeds your standard. How do you trace it back to the root cause, and then how do you mitigate the issue with that particular tank? The first step is to check the dO2 in your fermentation or aging tank. If it’s just a few ppb, take your portable meter and move to a sample point just before the BBT. If your dO2 still looks great, then it’s a good bet that air in the BBT before filling is causing your high readings.

But what if you saw a high reading in the sample right before the BBT? In that case, go back to the fermentation vessel and start looking again, moving to the next sample point. Keep moving toward the BBT. As soon as you find significantly higher readings, leave the analyzer in place and systematically move backward through the process to make sure that all valves, fittings, and pipe connections are tight. Then look at levels before and after pumps, filters, and centrifuges — any fitting that could possibly contribute. It may be as simple as a valve that’s open on the suction side of a pump.

Now, let’s say you’ve looked at all the possible culprits and your high dO2 is happening after a pump or centrifuge. What do you do? Some pumps and centrifuges can seem fine when they start, but as they heat up from use, they pull more oxygen into the beer. By checking the dO2 levels at different times throughout your filtration process, you can really zero in on whether or not heat and excess load are causing problems.

I have a customer who occasionally monitors their whole filtration run by placing a portable dO2 analyzer with on-board data logging on the filter outlet, collecting data throughout the entire filtration process. By doing this every so often, they’ve been able to determine when it’s time to rebuild pump seals. His pump load was increasing toward the end of the run due to the increased pressure it took to push the beer through the filter, so his O2 levels would start to climb drastically.

My final thought brings us back to my blog post from last Thursday. Measuring during or just after any movement of beer will help you recognize whether there is a significant infusion of oxygen into your product.  If things looked good at the beginning of a run, but not so great at the end, you can probably pinpoint the problem by monitoring throughout the run the next time you move your beer.

When to Measure the Dissolved Oxygen in Beer

Many years ago I was at a brewery where we were measuring the dissolved oxygen in a finished beer tank.  The dO2 was twice their acceptable value, so I asked what they were going to do with that particular batch.  The reply from the quality person was, “We’ll wait until tomorrow before sending it to packaging.  By then the dissolved O2 will be within spec.”  I gulped and politely asked if they were concerned with the long-term flavor stability of that tank of beer.  He changed the subject and we moved on to discuss other matters.

Brewers are much more concerned with minimizing dissolved oxygen today, because they know that the lower the dO2, the better the shelf stability. But not everyone understands how important it is to measure dO2 in real time.  Measuring a day or even a few hours after filtration or packaging won’t give a realistic measurement. If you bottle condition or don’t filter your beer, the oxygen consumption could be even faster: minutes instead of hours or days.

The key is to measure dO2 in real time, perhaps checking a bright beer tank a couple of times during a filtration run, or having inline monitors to insure that your centrifuge, filter, or pump are not creating a dO2 problem.

My final thought is that if you want to know the dissolved oxygen content of a particular batch, measure early.  Waiting could give you a false sense that all is well.  According to the White House Office of Consumer Affairs, 91% of customers who have a bad experience will not buy again from that business, and they will remember the offense for 23½ years.

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