Comment by patch_collector

It's actually quite public. The 'raw' doctrinal backing comes from 'Doctrine and Covenants, Section 89': https://www.churchofjesuschrist.org/study/history/topics/wor...

Clarifications as to what the 'hot drinks' section means has come over time, generally being shared during the twice-annual General Conference. The most prominent call came in 1921.

You can read more about it here: https://www.churchofjesuschrist.org/study/manual/revelations...