It is sometime difficult to separate truth from myth when determining how to get really low DO (dissolved oxygen) in the sealed cans during packaging. We’ll try to help set the records straight here. When we use the term DO, we usually mean TPO pickup, but that’s another topic. Let start with some myths.
Myth #1: The canning machine is the most important factor in reducing DO.
What, this is a myth? Coming from a canning machine manufacturer? Well mostly it is. Twin Monkeys will tell you our machines are all capable of getting DO pickup numbers (the amount of DO added during canning) below 30ppb. Other manufactures say similar things. The truth is that most of that isn’t the machine, it’s the way the machine is operated. If the operator doesn’t know how to properly setup the machine and watch for DO problem areas, the setup will produce very high DO levels and the problem isn’t the machine. All machines should be capable of getting low DO numbers IF they are operated correctly (more on that below). The operator setup is the most important factor.
Myth #2: Counter pressure (isobaric) filling produces lower DO than open filling.
Considering that both types of fillers finish the fill with the cans open to atmosphere and then pass the cans open to a lid applicator and then on to the seamer, the only difference in these systems is what happens during the fill.
In open filling with beer the cans are first purged with CO2 prior to filling. That pushes out a lot of the air/oxygen so that the fill can then take place in a mostly-CO2 environment. During the fill, a properly setup canner will generate enough foam to form a protective barrier for the headspace of the can until a lid can be applied.
In isobaric filling, the can is sealed and pressurized. If the canner isn’t equipped to purge at a station prior to sealing the can then at this point air is trapped in the can under pressure. The filler must then purge air from the can by introducing CO2 at the top of the can in a way that replaces the air inside the can. This takes time to do when and while this is happening, cans can’t be filled. However, it’s important to purge well during this stage because THIS IS WHERE THE PROBLEM WITH COUNTER PRESSURE IS. Once the fill starts, the pressurizes gas in the can will interface with the liquid and the surface area between the liquid and the gas is greater than an open filler on most (not all) counter pressure setups.
In the end, the final DO/TPO numbers in the can will tell the story and if you ask people owning various machines the open fillers are often producing better DO numbers than their isobaric counterparts, but that could be operator setup (back to Myth #1).
Myth #3: You can consistently get low DO numbers without a DO meter.
If you have good practices, you will have good (low) numbers, right? Good practices (more on that below) will help but you won’t know if there is one fill head that has higher DO pickup than the others or that you have a leaking seal bringing in air or that someone shut off the CO2 purge at some point if you’re not able to measure and tune your system. If you really want low, low numbers, spend the money on a meter and then tune up your system with the help of the feedback from the meter so that as you turn variables up/down, you understand the results on your finished product. At that point, you’ll want to understand the difference between TPO, DO and HO to help know where the problems are coming from.
Now that we’ve covered some of the misconceptions, let’s talk about what you should be doing to minimize oxygen in your finished cans
Best Practice #1: Cap on foam
Probably more than anything, the protection the foam on the top of a filled can gives until it’s lidded is the biggest factor you can do to minimize DO pickup. The goal is to get a mushroom of foam on the can that doesn’t spill over the sides, but will squish out as the lid is applied. The foam should be not have a furrow in it from dragging through a fill head as that valley makes it harder to apply the lid without trapping in air. This minimizes the chance of trapping air in the can when the lid is applied. Which leads to . . .
Best Practice #2: Underlid gassing
When the lid is applied, you don’t want the pocket on the bottom of the lid to trap new air in the can. Therefore it’s best to introduce low pressure CO2 behind the waiting lid and above the can coming into the lidder so that if a gas is trapped in with the can, it’s at least CO2, not air.
Best Practice #3: Foam scraper
There is evidence that larger bubbles (which rise to the top) contain more air than smaller bubbles. Scraping or popping the larger bubbles on the foam can help remove the problem bubbles right before the lid is applied.
Best Practice #4: Pre-fill purge
Before the fill process starts, it’s beneficial to replace most of the air in a can with CO2 or other inert gas. Then when the fill heads open, the beverage splashes into a CO2 environment were there isn’t a high oxygen content. During the fill the foam should start to do the work the CO2 was doing at the start and protect it until the cans reach the seamer.
Best Practice #5: Time between fill and seam
The longer the can is exposed to air once it’s filled but before it’s seamed, the more oxygen can find it’s way back into the can. Cans should immediately proceed from fill to seam without delay.
Best Practice #6: No air trapped in the beverage path
This starts with initial setup of the canning machine to the brite tank. The connecting hoses should all be free of air. How? Either pack the lines with de-aerated water or with CO2 prior to introducing beverage to the lines. Avoid high spots in the lines where pockets of air could remain. Use fill tubes that are always closed at the tips so they can’t bring in air between fill cycles. Everything should always have beverage in the beverage path with no gas pockets allowed.
Best Practice #7: Tight fittings in the beverage path
It is amazing how a tri-clamp or hose clamp fitting that isn’t tight enough can bring in air, but not leak liquid. Tighten all the connections in the beverage path to reduce chances of air intake as the liquid flows through it.
Best Practice #8: Proper purge and transfer techniques in the cellar
Face it, if your beverage already has high DO in the brite tank, it’s a problem the canning process will only make worse. Just like the two previous best practices apply to canning, they are necessary throughout cellar transfers. When prepping a brite tank, it must be properly purged of air before introducing beverage to it. If you can clean it without opening it (yes this is possible), then that’s the best way to keep oxygen out of a tank that’s already a pure CO2 environment.
Best Practice #9: Eliminate drafts
A significant problem with some canning line setups is when there is an air current that is allowed through the canner. This could be a nearby fan, or just a cross-breeze in the facility trying to cool down the hard-working canning crew. The problem is that the breeze will take away the CO2 blankets that are around the cans and lids and push in air instead.
Best Practice #10: Use proper rinsing liquids
It is possible to further reduce oxygen in the package if you’re not introducing any in your rinse process prior to fill. Using de-gassed water or ionized air to rinse eliminates the possibility of leaving water droplets that may contain some oxygen and carry through to the sealed can. Make sure the cans drain well, removing most of the water possible.
Best Practice #11 (for open fillers only): Tune the withdraw of the fill heads
Open fillers have beverage filling tubes that drop to the bottom of the cans. They take up room and displace liquid. If you fill the cans completely, then bring up the fill heads, the liquid level will drop and can pull in some air. You are better off finishing the fill process with the fill tubes nearly withdrawn from the cans. But it’s worse if the fill heads are totally withdrawn from the cans and still dispensing. That splashing can introduce oxygen as well. Setup the filler so the filling stops when there is only the tips of the fill heads left under liquid.