Dissolved O2 Pickup from Fillers vs. Crowners or Seamers: Quick Tip on How to Tell the Difference

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.

 

Total Package Oxygen 101 – What You Need to Know to Calculate TPO

The following post is the second in a series on Total Package Oxygen (TPO).

We’ll cover two topics in this blog post: 1) The parameters you need to do a TPO calculation and 2) Best practices for getting packages to equilibrium.

First, TPO calculation parameters. It’s a paradox, but the actual calculation for TPO is both complex and simple. The complexity part arises from bits of Henry’s Law, Boyle’s Law, physical properties of water vapor, and atmospheric barometric pressure. But these complexities are incorporated in the calculations, so the simple part is that in order to do our calculations, all we really need are these easily obtained variables:

Dissolved oxygen content
The package must be shaken, so the gases in the headspace and liquid are at equilibrium.

Liquid volume
Accuracy of liquid volume is not very critical, so using the average package fill will give a statistically valid TPO.

Headspace volume
The more accurately we can determine the headspace volume the more accurate the measurement. Knowing it to within 1 mL is best.

Package temperature
There are a lot of variables that rely on the package temperature built into the TPO calculation, so it is best to measure to within 1 oC.

So now we know our important package parameters. But how do we know we’re measuring our packages at equilibrium, so our calculations will be correct when we plug them into our formula?

We shake (equilibrate) packages in order to mix dissolved gases in the liquid with air trapped the headspace after the closure has been applied to the package. The question is: how long to shake the package?

People have tried all sorts of things through the years to determine the proper amount of shaking time. In the end it turned out that one of the best methods was to take old cans of beer with less than 2 ppb of dO2 and inject known volumes of air into the cans. By doing that and then shaking for various amounts of time, it could be determined how long it takes to be able to account for 100% of the oxygen when measuring TPO using the dissolved oxygen concentration and the other parameters outlined above.

Using a platform shaker at a minimum of 180 revolutions per minute, room temperature packages take 3 minutes to equilibrate. Packages at 5 oC, on the other hand, do best with 5 minutes of shaking. The basic rule of thumb is that the colder the package, the longer the shaking. When shaking cold packages, it is also important to remember that the temperature of the package is constantly trending toward room temperature, so the best practice is to shake continuously until you are ready pierce the package.

One short note on bottle conditioned beer: I’ve seen yeast so active upon packaging that they can consume statistically significant amounts of oxygen in the time it takes to shake a bottle, so I’ll have some hints about how to deal with that next time.

My final thought is to always shake thoroughly and consistently. Using some sort of a mechanical shaker will decrease operator error and insure against inconsistent results.

 

Total Package Oxygen 101 – TPO Defined

The following post is the first in a series we’ll do covering Total Package Oxygen (TPO).

In the late 1980s I worked on a research and development team — funded by a crown manufacturer — with the goal of creating oxygen-scavenging polymers for beer bottle closures. The project went through numerous challenges (think scorched plastic) and dicey prototypes (think raised eyebrows at the FDA). In the end we were successful, but by far the biggest and most important challenge was learning how to quantify the efficiency of our oxygen scavenging polymers. In other words, exactly how much oxygen did the polymer coated closures remove from bottled beer?

It turned out that the ticket was to measure Total Package Oxygen (TPO). We’ll talk about our method in a minute. But first, what exactly is TPO? Simply put, TPO is defined as all of the oxygen in the package: headspace and liquid. We can also just say that TPO is all of the oxygen available to react with beer in a package. In order to get an accurate TPO, we need to know four things: dO2, headspace volume, liquid volume, and temperature.

We’ll cover the importance of volume and temperature in a future post, but for now let’s talk about the first parameter: dissolved oxygen. For our project, we knew that measuring headspace oxygen alone wouldn’t do, because experience had taught us that beer itself has a really fast oxygen uptake, and we needed to know how well our polymers were scavenging.

So we thought a bit more about the oxygen content of a package just after filling. We already knew we had gas in the headspace of the bottle or can, and gas dissolved in the liquid. The dissolved oxygen was whatever was present in the beer before filling, plus any oxygen picked up during the filling process. The headspace oxygen, on the other hand, was air left over in the headspace after a closure was put on the bottle or can.

So there we were, with two distinct partitions of oxygen in the package — dissolved and headspace – and yet we wanted to measure using a portable dO2 analyzer. How were we to do that and still take into account the headspace O2? It turned out that the answer was a bit James Bond: the package needed to be shaken. (Not stirred!) We found that if we shook the packages properly, the gas in the liquid and the headspace would equilibrate to the same partial pressures. Once the gas was at equilibrium, we could use our portable dO2 analyzer to measure the dO2 in the liquid.

Since then, many TPO techniques have been developed that measure variations of dissolved oxygen, headspace oxygen, and a combination of headspace and dO2.  Different techniques have different advantages, but for now I just want to assure craft brewers that it is possible to do accurate dO2 measurements in pursuit of a TPO goal using one of your simplest tools: a portable dO2 analyzer.

My final thought is to emphasize the importance of making sure your packages are at equilibrium. If a can or bottle is not properly shaken, then your TPO may be either under or over estimated.

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