This has come up in a few different threads and i haven't seen it posted here before.
What happens to the open alcohol?
Someone asked an FA on SQ who said it was thrown out, others report half open bottles at the start of a flight.
Others say they pour the wine and cheap spirits out, but put the high end stuff in a special container which is sealed until in the air. (which i think seems right, as i doubt they throw out $500 bottle with one nip taken out each flight)
And they pour the cheaper stuff while on the ground (J and F) cause they have to pay duty on these, then have the better stuff available when duty does not need to be paid