Mitigate Package Risk of Package Failure with Head Space Management
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 is 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 more to insure a margin of safety. Contact QuantiPerm for a more accurate
analysis of specific products and packaging scenarios.
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.
