100:3 A kohein may not drink wine or other alcoholic beverages before duchening. If he feels weak and wants to eat some cake before musaf, he should listen to another person making Kiddush. (A kohein who drank a reviis – about 3.5 ounces – of wine at one time may not duchen – OC 128:38.)
100:4 Before going up, a kohein must wash his hands up to the wrist, the same way the kohanim sanctified their hands in the Beis HaMikdash, as per Psalms 134:2, “Raise your hands in the Sanctuary and bless Hashem.” There is a doubt whether or not the kohanim should recite a bracha over this hand-washing. since they recited the bracha on hand-washing when they got up in the morning. Because of the doubt, the practice is not to recite a bracha. If, in the interim, the kohein touched an unclean place, it would be appropriate to recite a bracha over the later hand-washing, but such is not our practice. It’s proper for every religiously-zealous kohein to protect his hands from such contamination after the morning hand-washing in order to avoid the possibility of needing to recite another bracha.