To beer or not to beer: does tapping beer cans prevent beer loss? A randomised controlled trial

Objective: Preventing or minimising beer loss when opening a can of beer is socially and economically desirable. One theoretically grounded approach is tapping the can prior to opening, although this has never been rigorously evaluated. We aimed to evaluate the effect of tapping a can of beer on beer loss. Methods: Single centre parallel-group randomised controlled trial. 1031 cans of cans of beer of 330mL were randomised into one of four groups before the experiment: unshaken/untapped (n=256), unshaken/tapped (n=251), shaken/untapped (n=249), or shaken/tapped (n=244). The intervention was tapping the can of beer three times on its side with a single finger. We compared tapping versus non-tapping for cans that had been shaken for 2 minutes or were unshaken. Three teams weighed, tapped or did not tap, opened cans, absorbed any beer loss using paper towels, then re-weighed cans. The teams recorded the mass of each can before and after opening with an accuracy of +/-0.01 grams. Main outcome measure: The main outcome measure was beer loss (in grams). This was calculated as the difference in the mass of the beer after the can was opened compared to before the can was opened. Results: For shaken cans, there was no statistically significant difference in the mass of beer lost when tapping compared to not tapping (mean difference of -0.159g beer lost with tapping, 95% CI -0.36 to 0.04). For unshaken cans, there was also no statistically significant difference between tapping and not tapping. Conclusion: These findings suggest that tapping shaken beer cans does not prevent beer loss when the container is opened. Thus, the practice of tapping a beer prior to opening is unsupported. The only apparent remedy to avoid liquid loss is to wait for bubbles to settle before opening the can.