Frivolous Friday Fun – What’s a Churchkey?

When I was a kid we had a drawer in the kitchen that held a half-dozen can openers designed by American Can Company. The ones we called “churchkeys” were used to pierce flat-topped steel cans, long before the invention of the tab pull opening.

Now a company in the Northwest is attempting to revive the flat-topped can.  From what I can tell by looking at their video, it is a three-piece can that appears to be made from steel instead of aluminum.  Here’s the link.

This of course made me think of our old chuchkeys and that in turn made me wonder how the term was coined in the first place. It turns out – no surprise! – that controversy abounds, and that if one wants to go deep into this topic there may be no limit:  Link here.

Happy weekend!


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.


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