It is well known that the Beracha of Hamosi recited on bread exempts the other foods he subsequently eats in the meal. Similarly, the Beracha of Hagefen on wine exempts all other beverages that he will subsequently drink from the Beracha of Shehakol normally recited on them.
Not only does the initial Beracha of Hagefen exempt the other beverages from their initial Beracha, but the Beracha Aharona of Al Hagefen, recited after drinking a Revi’it (3.2 oz.) of wine, exempts the other beverages from the "Boreh Nefashot" normally recited after drinking them.
Hacham Ovadia rules that if one drank less than a Revi’it of wine, but drank more than a Revi’it of water, he must recite the Beracha Aharona of Boreh Nefashot on the water, even though he did not say a Shehakol on the water. He cannot say the Beracha Aharona of Al Hagefen, since he did not consume the requisite amount of wine.
Hacham Ovadia compares this to the following interesting case in which one recites a Beracha Aharona on a food, even though he did not recite a Beracha Rishona on it. Generally, bread is the primary food and its Beracha of Hamosi covers everything else. However, if the bread is eaten solely for the purpose of dampening the spicy or salty taste of another food, the Beracha is recited on the other food. For example, if someone eating very salty anchovies eats a piece of bread with them to dull their salty flavor, he recites Shehakol on the anchovies and exempts the bread. If he ate a Kezayit of anchovies, he recites the Beracha Aharona of Boreh Nefashot, which covers the bread as well. However, if he did not eat a Kezayit of anchovies (and therefore they are exempt from any Beracha Aharona) but did eat a Kezayit of bread, he would recite Birkat Hamazon on the bread, even though he did not make Hamosi on the bread.
These complex cases illustrate the importance of thoroughly learning the Halachot of Berachot. Without this, one will not know how to act properly. That is why the Gemara requires one to go to a Talmid Hacham to learn these Halachot, before the cases arise.
