This procedure determines the CO2 shelf life of a given carbonated beverage container by evaluating the CO2 level within sample bottles over time using a CarboQC test instrument.
The CarboQC uses an automated piercing method, which improves test repeatability as well as operator-to-operator test reproducibility relative to tests using a manual piercing method. It also corrects for the amount of air in the package and reports both the volumes of carbon dioxide with the impact of air factored out and the parts per million of air in the sample.
Sixty bottles are carbonated to 4.2 ± 0.1 volumes CO2 and then stored in a constant temperature chamber at 72°F, 50% RH for the duration of the test procedure. Six bottle samples are destructively evaluated using the CarboQC to measure pressure and temperature data to calculate volumes of CO2 at the following intervals: 0 hrs, 24 hrs, 2, 4, 6, 9, 12, 16, 20 and 24 weeks.
Packages are sampled by piercing them through the top panel of the closure with an automated sampling tube, then drawing a fixed volume of liquid into a test cell. After the aliquot has been drawn into the cell and equilibrated by agitation, the cell is expanded by first 10%, then by 30%, with the pressure and temperature being measured after each expansion. The pressure at 10% sample chamber expansion, the pressure at 30% sample chamber expansion, and measured temperatures are then used to calculate the CO2 volumes contained within the bottle and the average % CO2 loss per week is determined. The value of CO2 volumes calculated by this method is corrected for the air content in the sample. This correction is possible because of the differences in solubility of CO2 and air in water. As the test cell expands, the pressure contributed by CO2 will remain the same as more CO2 is pulled from the liquid phase, while the pressure contributed by air will drop as there is relatively minimal air dissolved in the liquid phase that can be drawn out to further fill the expanded cell headspace. Air content is also reported as parts per million of air. This test measures the CO2 loss from the entire package (bottle and closure) not just the bottle alone, as does Zahm & Nagel testing.
Differences from manual Zahm & Nagel testing:
- CarboQC measurements are more repeatable and reproducible because of the automated piercing and sampling.
- The CarboQC reports a more accurate CO2 content as the calculations subtract the pressure contribution from air or nitrogen.
- The CarboQC reports amount of air content in ppm in addition to volumes of CO2.
- Volumes of CO2 as reported by CarboQC will be nearly identical to volumes reported by Zahm & Nagel methods if the water is effectively de-aerated prior to carbonation as it is in many production filling operations. If the water is not de-aerated prior to carbonation, total pressure in packages measured by CarboQC to have the same volumes will be higher in package pressure by an amount proportional to the amount of pressure in the package due to air content. This higher pressure will vary depending on how much air is entrained in the water being used for filling, which depends on water temperature among other variables. Use of water without effective de-aeration will typically add pressure equivalent to another 0.2 to 0.5 volumes of CO2 content. Since this added pressure will lead to more tension stress for a package filled to a given “CarboQC volumes” than would be experienced by a package filled to the same nominal “Zahm & Nagel volumes,” it is critical that everyone who will use the results of the testing understand the effects of this difference on testing results.