The temptation to quickly chill a warm can of soda in the freezer is common. Leaving a carbonated beverage in the freezer for too long results in a sticky mess. This household disaster is a direct consequence of fundamental physical and chemical principles acting on the container. Understanding what happens involves examining how water solidifies, how dissolved gas reacts to this change, and the combined pressure this generates.
The Anomalous Expansion of Water
The primary force stressing the container is the peculiar behavior of water when it changes from a liquid to a solid state. Unlike nearly all other substances, which contract as they freeze, water undergoes an anomalous expansion. This occurs because water molecules form an organized, open hexagonal crystalline lattice structure as they freeze, holding the molecules farther apart than they are in the liquid state.
Since soda is largely composed of water, this phase change causes a significant increase in volume. When water freezes, its volume expands by approximately 9%. Within the rigid confines of an aluminum can or glass bottle, this expansion generates significant internal force. The liquid essentially tries to occupy more space than the container can physically offer.
How Carbonation Accelerates Container Failure
Liquid expansion is only half of the story; the second contributor to container failure is the dissolved carbon dioxide (CO2). Carbonated beverages are bottled under pressure to keep the CO2 gas dissolved in the liquid, a process reliant on Henry’s Law, which states that gas solubility increases with pressure and decreases with temperature. When the water begins to freeze, the CO2 is forced out of the solution entirely because gases are far less soluble in solid ice than in liquid water.
The freezing process concentrates the CO2 into the remaining liquid and the headspace at the top of the container. This rapid exclusion of gas dramatically increases the pressure within the headspace. The combined force of the expanding ice pushing outward and the concentrated CO2 gas pushing on the can walls quickly exceeds the container’s structural limits. This dual-action pressure ultimately leads to the rupture.
Practical Outcomes and Safe Quick-Chilling
The immediate outcome of forgetting a soda in the freezer is a ruined beverage and a difficult cleanup. If the container ruptures, the high-pressure spray covers the freezer interior with a sticky, frozen soda residue. Even if the container remains intact, the resulting slush will have a significantly diminished taste and texture. The exclusion of CO2 from the freezing liquid means the thawed soda will be flat, having lost its characteristic fizziness.
For those needing a drink chilled quickly and safely, there are better methods that avoid the risk of rupture. One effective technique is the wet paper towel method, which involves wrapping the can in a damp paper towel and placing it in the freezer. The evaporation of water from the paper towel acts as evaporative cooling, rapidly drawing heat away from the can’s surface and cooling the beverage in about 15 minutes. A more efficient method uses a bath of ice, water, and salt. Salt lowers the freezing point of the water, allowing the mixture to reach a temperature well below 0°C while remaining liquid. This super-chilled water provides a much better medium for heat transfer than cold air, cooling a can in as little as five minutes.