Ethanol acts as a wetting agent, so in an alcoholic drink the
submerged slice of apple holds too little air to float the non-buoyant,
sugary cherry. The assembly will thus sink, though if you add soda,
enough bubbles might attach to the apple to make the whole thing float
again.
Human sloshing complicates insights after the fourth
glass of appletini, but buoyancy is a more complicated affair than
density considerations might suggest. For example, a boat that is
seaworthy might sink if capsized.
Try dropping a clean, dry pin or razor blade gently onto a
glass of still, pure water. Dropped endwise the object sinks; the metal
is too dense. But surface tension will support the item if you gently
drop it flat onto the fluid, especially if the metal is lightly waxed or
oiled.
The behaviour of your appletini garnish is similar in
some ways. The waxy skin and the broad shape of an unpeeled slice of
apple on the surface of the drink can resist both the wetting and the
shipping of fluid over the edge of the slice.
The stimulation of considering this question's
complications should mitigate the brain-addling aspects of appletini,
though, sadly, not to the extent of fully reversing them.
Antony David, London, UK
