  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.
