Research Brief

The video demonstrates a popular folk technique claiming that tapping a shaken carbonated beverage can four times around its edge prevents spray by dislodging CO2 bubbles from the walls. The scientific reality is far more nuanced and largely contradicts this claim. When a can is shaken, carbon dioxide comes out of solution and bubbles form on the inside, and opening it causes a sudden drop in pressure that makes bubbles grow much larger and triggers new bubbles to form at nucleation sites. The theory behind tapping suggests that tapping dislodges tiny bubbles from the walls of the can and causes them to rise to the top, so when opened, gas can escape without carrying liquid.

However, the most rigorous scientific test of this technique—a 2019 randomized controlled trial by researchers at the University of Southern Denmark—definitively debunked the tapping method for beer. For shaken cans, there was no statistically significant difference in beer lost when tapping compared to not tapping (mean difference of -0.159g), and these findings suggest that tapping shaken beer cans does not prevent beer loss when the container is opened, with the only apparent remedy being to wait for bubbles to settle. The study tested 1,031 cans of Carlsberg beer, with half shaken for 2 minutes to simulate bicycle transport. BBC Science Focus notes that tapping the sides might help dislodge bubbles so gas is at the top with fewer nucleation sites, but it's only partially effective, and leaving the can to stand for a minute works better. Multiple experimental sources confirm that tapping a can of soda does absolutely nothing to reduce foam and it is actually the short time interval taken to tap the can that is reducing foaming versus simply opening the can immediately. The Danish researchers theorized that beer proteins that contribute to creaminess may trap microbubbles in the liquid and prevent them from rising at all, though the tapping method may still work for other fizzy drinks that do not contain these molecules.