The halacha is that the bracha on wine covers other drinks [if they are in front of you or you had them in mind]. There is a machlokes in the poskim whether even a TASTE of the wine covers other drinks or only if he drinks a SIGNIFICANT AMOUNT of a cheekful [מלוא לוגמיו].
I had a safek if this מלוא לוגמיו must be drunk in one shot, as we find that one is only obligated to make a bracha achrona on drinks [according to some opinion] if he drinks a רביעית in one shot. Or maybe it can be drunk little by little. [I did a search and found only one posek who related to this question but brought no proofs].
There is also a discussion whether this halacha also applies to grape juice. Maybe only wine covers other drinks because of the importance of wine but not grape juice - or maybe it applies to grape juice as well.
What is the root of the machlokes whether one needs to drinks a מלוא לוגמיו or even a taste is enough??
