This has been foreshadowed greatly.
1st look back at the first testing moment for Zoro with nothing happened, as he was incapacitated Luffy said we can fix him with Booze.
2nd at Fishman Island we learn why our 2 heroes don't want to be heroes, 1 won't share meat, the other won't share sake
3rd when shanks met a sick whitebeard he said I brought medicinal water (sake) from my home town (west blue) Wano is in the west blue
4th remember, luffy 1 hero ate an entire store of meat to re-energize,
Zoro the other will drink the rest of the sake gourd kaido left up top, the same sake that increased kaidos haki in 1037