A common scenario involves a shaken carbonated beverage and the concern of a messy foam eruption upon opening. Popular belief suggests that turning the can upside down or tapping its sides can prevent the resulting spray. This folk remedy is based on an intuitive understanding of the drink’s volatile nature. Investigating the physics behind this myth allows for a clear verdict on its effectiveness and the identification of reliable methods for opening an agitated can without disaster.
The Science of the “Explosion”
The energetic spray from an opened, shaken can results from carbon dioxide (CO2) gas rapidly exiting the liquid. Carbonated beverages are pressurized to force large amounts of CO2 into solution, a state governed by Henry’s Law, which dictates that gas solubility increases with pressure. When a can is sealed, the pressure above the liquid keeps the CO2 dissolved.
Shaking introduces kinetic energy, causing dissolved CO2 to leave the solution and form countless microscopic bubbles. These bubbles adhere to the rough inner surfaces of the can, acting as nucleation sites for gas aggregation. Because these tiny bubbles are distributed on the can walls, they are prevented from rising naturally to the top.
When the can is opened, the pressure inside drops instantaneously to atmospheric pressure, and the liquid can no longer hold the excess CO2. The microscopic bubbles stuck to the walls rapidly expand into much larger bubbles, acting as conduits for the remaining dissolved gas. Since these bubbles are positioned low in the can, their violent, upward rush displaces and pushes a large volume of the liquid out, resulting in a foamy spray.
Analyzing the Tapping Technique
The theory behind tapping or turning the can is that the physical shock dislodges the microscopic CO2 bubbles clinging to the inner walls. Once dislodged, the bubbles are expected to rise quickly to the headspace at the top of the can due to buoyancy. This action, if successful, would consolidate the gas layer above the liquid.
The goal of consolidation is to minimize nucleation sites remaining in the liquid. If the bubbles are concentrated in the headspace, the expanding gas escapes primarily from the top when the can is opened, without pushing liquid out. Turning the can upside down is thought to help this process by forcing the gas to travel the entire length of the can. However, the force required to detach all microscopic bubbles from the can lining is substantial.
Scientific Verdict and Proven Methods
The scientific consensus is that the tapping technique is largely ineffective. While the principle of dislodging bubbles is sound, the kinetic energy from a few taps is insufficient to detach the vast number of microscopic bubbles created by vigorous shaking. Furthermore, tapping can inadvertently introduce more agitation, generating new bubbles or delaying the inevitable eruption.
A more reliable method is simply to wait, allowing the natural physics of the liquid to take effect. If left undisturbed for a few minutes, the CO2 will naturally begin to re-dissolve into the liquid or consolidate into the headspace. For an immediate solution, the safest strategy involves opening the can very slowly, allowing a minute amount of gas to escape at a time. This slow release, sometimes called “burping” the can, gradually reduces the internal pressure, preventing the explosive expansion of gas pockets.