TPO – The Importance of Shaking Packages When Using a Dissolved Oxygen Monitor

When a dissolved oxygen monitor is your only option for measuring package oxygen content, the best way to calculate the total package oxygen (TPO) is from a shaken  (equilibrated) container. In my last blog post I wrote about what you can learn by measuring unshaken packages. This time we’ll focus on equilibrated packages, which are containers that have had sufficient shaking to bring the gases in the headspace and liquid to equilibrium. First, let’s define equilibrium.

The gases in the headspace and liquid of a package are in equilibrium when their partial pressure (also called percent concentration) is the same. The only way to create equilibrium after filling is to shake the package, so that the gases move from the area of higher concentration to the area of lower concentration and are finally distributed equally.

Packages can be shaken by hand, but if you’ll be shaking a lot of packages then you’ll probably want to use a rotary platform package shaker.

Packages must be shaken for different lengths of time, depending upon their temperature. This is because warm packages reach equilibrium faster than cold packages. As a general rule, warm containers need about three minutes of vigorous shaking and cold packages need about five minutes. When shaking cold packages, it is important to keep shaking the container up to the point of use and not let the package warm after the shaking is completed. If the package warms between the time it was shaken and the time it’s measured, then the oxygen partitioning in the package will have changed and you may underestimate the TPO.

What does a shaken package tell you? Since packages come off fillers with different amounts of gas in the liquid and headspace, the most practical way to calculate the total gas content is to equilibrate them and then make your dissolved oxygen measurements. If you measure the dO2 of a freshly filled package without shaking, then you’re only determining the oxygen content of the liquid, without any feedback as to whether there was sufficient fobbing of the headspace.

Knowing the TPO not only helps you determine exactly how much oxygen is trapped in the container and can react with the beer, but it also allows you to calculate the headspace contribution to the package oxygen concentration. The headspace oxygen of a package is the TPO minus the dissolved O2:

Headspace O2 = TPO – unshaken dO2

My final thought is that if you want to measure the TPO of your packages using a dissolved oxygen sensor, you must shake the packages and measure the dissolved oxygen in as short a time frame as possible. Since different beer types have different residual package O2 consumption rates, understanding your specific beer will also help you know just how quickly this needs to be completed. We’ll talk about that in a future post.

For a review of a previous post on what you need to know to measure total package oxygen, follow this link.

Beer Sensory – Creating a Basic Plan for Beer Storage

 

I was talking to a brewer about TPO and he asked if minimizing oxygen pickup at the filler might help extend his shelf life and limit sensory changes as his beer ages. He was mainly concerned with controlling beer in the distribution channel, but when I quizzed him about how he calculates the pull dates for his product, he admitted it was mostly a guess. He said there were significant differences in his beer after it had been sitting on a shelf in a store, but he hadn’t tried to mimic that aging and study the changes in a controlled setting.

Oxygen pickup is definitely the most critical component in the development of off-flavors in beer, but many other things can be a factor too, so careful studies of the way your beer ages can help you make informed decisions. Here are some ideas that might help.

First, if you haven’t already done it, then consider getting formal training in sensory. You no-doubt know your product very well, but learning the standard terms and techniques of sensory can be a lot of fun and can give you a good foundation to stand on as you start keeping records. I was with a company that hired a sensory specialist to come in and work with us over the course of a year and it was some of the most valuable training I’ve ever received.

Next, set up a system for comparing your stored beer in different environments over time. I once worked with a closure manufacturer to develop oxygen-scavenging polymers for crown closures. We established a taste panel to evaluate everything from how the polymer affected beer taste to how well the crowns worked to minimize oxidative flavor formation. Depending upon what we wanted to learn, we had different methods for beer storage and comparison.

Our most basic protocol called for storing a set quantity of the same beer (all from one run, one filler) in different ways, typically one case stored cold, one at room temperature, and another upside-down at room temperature.

The cold beer was the control, since sensory changes are accelerated by heat. The room temperature samples were to see what changes developed in non-harsh conditions. And the upside-down bottles at room temperature were to minimize effects of oxygen ingress through the closure, so we could see how well they worked. This can be done with canned beer too, but you shouldn’t need to store the beer upside down unless you are concerned with poor seaming.

Next, you can see how your beer responds to harsh conditions and other variables. Punish it by exposing it to heat, like might happen in a hot delivery truck. Or maybe you’re concerned about closure polymers affecting taste. To analyze this, gently heat lined caps on a hot plate and remove the liner material with tweezers as soon as it gets soft, then put them in the beer, fob it, and re-seal. When you taste it days or weeks out, you should be able to detect things like flavor scalping or off-flavor pickup.

Once you’ve established a system for storing and evaluating your beer under different conditions, make sure you check it on a regular basis. It’s probably not necessary to do it every day, but in addition to tracking sensory changes over time and in different conditions, it can be helpful if there is something in your process that changed, like a new source of ingredients or filling issues.

My final thought is to get to know your beer. Compare it with both beer packaged at the same time and with beer that is older or younger. By understanding sensory changing factors, you may be able to comfortably lengthen the time you beer is in the distribution channel by weeks or even months.

O2 Impurity in Carbon Dioxide: How Much is Too Much?

I recently saw a post on a brewing forum where someone was wondering about air contaminated carbon dioxide and its impact on dissolved oxygen levels in carbonated beer. Air in CO2 really can raise the dO2 levels in your beer, so I thought it would be worth discussion.

Back sometime in the late 1980s (I think) someone passed along to me a table showing the exact amount of dO2 that would be picked up in beer if specific amounts of CO2 were injected into a process pipe or finished beer vessel. I’ve been hoping to find a copy of that article ever since, so maybe someone out there can help steer me to it. But in the meantime, with a tip of the hat to the original author(s), here is a copy of the table:

Co2 Injected O2 Impurity

0.001%

O2 Impurity

0.005%

O2 Impurity

0.02%

0.5 V/V 7 ppb 35 ppb 142 ppb
1.0 V/V 14 ppb 71 ppb 284 ppb
2.0 V/V 28 ppb 142 ppb 567 ppb
Dissolved oxygen added to the beer during injection

So knowing all of this, what’s the best way to determine whether a CO2 supply is contaminated with air? There are two approaches. First is to simply measure your CO2 source in the gas phase using a low-level oxygen sensor that is accurate to at least 0.001%. The other is to measure the dO2 in your beer before and after CO2 injection. If you are measuring in the beer, use a measurement point that is furthest from the injection point so that the gas will have a chance to dissolve into the beer as much as possible before you measure. If you carbonate in a tank, just measure in the tank.

My final thought is that you may be doing everything right in the rest of your process, but if the CO2 you’re using to trim your carbonation is loaded with air, your beer may pick up a significant amount of oxygen.

Have you seen the article with the CO2 table? If you can point me to the journal and/or author, I’d be happy to post a reference.  Please leave the information as a comment below.

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