Beverage packages, be it cans, bottles, kegs, or even tanks and totes can experience increasing internal pressures when the temperature warms up. While vendors have specifications on the maximum pressure they can withstand, it becomes the responsibility of the beverage manufacturer to ensure that once the package is filled, the internal pressures never rise above the maximum safe levels specified by the supplier for the maximum temperatures that the package experiences during its journey through the distribution chain. For pasteurized beverage products, the maximum temperature the beverage experiences is likely the pasteurization temperature.
Once you fill a package with beverage and close it, as the package warms up, the beverage expands slightly causing the internal pressure to rise. The change in the liquid density is generally quite small to be a significant issue – most of the time there is enough of a head space volume to shrink and accommodate whatever increase in space the liquid requires. If there is no head space in the package, it is indeed a recipe for disaster unless the packaging is specifically designed. For example, vacuum filled packages, hot-filled beverage packaging retort containers and such packaging usually allows for the container volume to change harmlessly to a predetermined set of design parameters.
The expanding liquid can exert great forces on an otherwise rigid, unyielding container. If the seals (bottle closure, can seams) don’t fail sooner and if the stresses thus built up exceed the material yield strength, the package can rupture.
The problem can become acute when there is dissolved gas involved. For carbonated beverages (or nitrogenated beverages for that matter) even small changes in temperature can cause significant changes in internal pressures. Suddenly, the risk of packaging failure can be quite real. Is that head space you provided adequate? What if you have too much head space, or not enough carbonation? Consider also the possibility that when the package cools below the fill-time temperatures, the internal pressure might decrease! You don’t want the can to feel mushy when the temperature drops! Will such cans stack well on pallets in distribution?
Fortunately, almost all packages have at least some head space and the risk of failure is small. Yet, there are ways to insure your packaging stays in the safe zone. Using thermodynamic models for gas solubility and partition coefficient, it is possible to model pressure changes in a package as its temperature changes from that of the filling conditions. The attached data tables are generated by modeling how the package pressure changes as the temperatures change once the package has been filled. Thermodynamic gas solubility models are derived from NOAA tables and Chemical Engineers’ Handbook. The package is assumed to be filled at defined initial conditions (beverage carbonation and fill level/head space fraction).
Conclusions: It is clear that no matter what level of carbonation we are dealing with, allowing for a finite amount of head space provides additional margin of safety by mitigating pressure rise in the package as the package warms up.
Pressure rise at pasteurization temperatures can be quite dramatic and can easily approach package design limits, especially for higher carbonation products (last columns in each of the tables).
Estimates provided in the last column are derived by extrapolating QuantiPerm’s proprietary solubility data. The higher temperatures encountered during typical pasteurization scenarios falls outside the range of guaranteed accuracy, but nevertheless provide an assessment of the pressure risks. If your product is going to be pasteurized, the package must withstand at a minimum these pressures and more to insure a margin of safety. Contact QuantiPerm for a more accurate analysis of specific products and packaging scenarios.
Murthy Tata
Application Notes:
- Note that the pressures listed in the attached tables strictly represent the gage partial pressures of CO2 when the packaging operation is conducted at sea level.
- If any air is entrained while packaging (e.g., non-foaming beverage can without undercover CO2 gassing prior to closure application), the air adds to the CO2 pressure to inflate the final pressure. At worst, this may add as much as 14.7 psi
- Remember to correct the pressures for packaging operations at elevations different than sea level. At higher elevations, the net package gage pressure is inflated. Add 14.7 psi to the table pressures and subtract the local atmospheric pressure to estimate the net package gage pressure.
- Undercover gassing with other inert, non-CO2 gases (e.g., N2, Ar) should be treated as in (2) above. If any liquid nitrogen dosing is conducted, the elevated pressures should be similarly considered.
- While air in package will directly increase the package pressure, even small levels of package oxygen may cause corrosion in aluminum cans while only minimally impacting the pressure. Elevated package oxygen levels can not only impact flavor stability of susceptible products but also elevate the risk of corrosion in aluminum cans. Corrosive metal failure must be regarded as another mechanism that essentially causes the packages to rupture at pressures well below those listed in the tables. Consult the can supplier specifications for maximum allowable package oxygen levels.
Table 1. Estimated (gage) pressure in the package at various temperatures and head space fraction – Stock beverage carbonation 2.65 v/v.
* Model calculations for last column (pasteurization temperature) are only extrapolations from QuantiPerm’s solubility data for CO2 and are as such approximate. Consult QuantiPerm for additional details.
Table 2. Estimated (gage) pressure in the package at various temperatures and head space fraction – Stock beverage carbonation 3.0 v/v.
* Model calculations for last column (pasteurization temperature) are only extrapolations from QuantiPerm’s solubility data for CO2 and are as such approximate. Consult QuantiPerm for additional details.
Table 3. Estimated (gage) pressure in the package at various temperatures and head space fraction – Stock beverage carbonation 4.0 v/v.
* Model calculations for last column (pasteurization temperature) are only extrapolations from QuantiPerm’s solubility data for CO2 and are as such approximate. Consult QuantiPerm for additional details.
QuantiPerm is your partner in beverage processing and packaging. We offer expertise and novel instrumentation in inline Carbonation, Degas and Nitro dispense technology! Our direct-to-filler carbonation option can save time, space and money! Carbonate from 0 to 4v/v and send your beverage (craft soda, cider, seltzer, kombucha, spirits and more) directly to your filler! We also offer a line of novel instruments, accessories, and test methods for bioprocess monitoring for the Biotech industry. Our instrumentation and testing services for the packaging industry includes permeation testing, barrier and shelf life determination, package oxygen testing to name a few.