3,973. When Kohanim May and May Not Drink

Hilchos Bias HaMikdash 1:6

The kohanim on a given week’s duty rotation in the Temple may drink wine at night, but not by day. Even the members of kohanic families who are not scheduled to work on a given day may not drink wine by day. This is out of concern that the Temple service will be too much for the family on duty that day and they will require members of the watch from other families to assist. The members of the family on duty on a given day may not drink by day or the preceding night. This is out of concern that they might drink at night and get up to serve in the morning without the wine having completely worn off.

Hilchos Bias HaMikdash 1:7

If a kohein knows from which watch he is descended, from which family he is descended, and the day on which that family performed the service, he may not drink wine that whole day. If he knows from which watch he is descended, but not from which family, he may not drink wine the whole week his family worked. If a kohein doesn’t know his watch or his kohanic family, then really, he should never be permitted to drink wine. However, his ignorance in this matter actually leads to a leniency and he may drink wine at any time. This is because such a kohein would not be able to perform the service until his kohanic family and watch are determined.