The Mishnah states that any time there is a food item that is the “main” item (ikkar) and is accompanied by a secondary item (tafel), a berakhah is recited on the ikkar and the tafel is exempted. As R. Shlomo Fisher (Beit Yishai, 65, fn 9) observes, there are two concepts relevant here. One is the concept of “tafel”, by which one item can become included with another item through accessory status. This is comparable to one who buys an item and receives the covering of the item for free with it.

The second concept is that associated with R’ Chiya (Berakhot 41a), that bread exempts all other foods [through its berakhah] and wine all liquids. In this case, there is no accesory; the other liquids do no service for the wine. Rather, the function here is one of prominence; bread is the most prominent of foods and wine of liquids. It is inappropriate to recite a berakhah over a [comparatively] insignificant food in the presence of an esteemed food. This is comparable to one who makes a large purchase and receives a free gift as a courtesy.

A crucial difference between the two concepts is that in the first, the “tafel” item is covered by a berakhah, that of the ikkar; in the second, the other foods are eaten without a berakhah.

The Magen Avraham (177:1) writes that one who is not interested in eating bread but nonetheless eats a little bit of bread and recites a berakhah, does not through this exempt other foods. This is because the halakhah does not follow R’ Chiya in the ability of bread to exempt other foods; rather, it is only when a meal is established through the bread that the other foods are considered to be “because of” the bread. However, if there is no interest in the bread, and certainly if it is less than a k’zayit, it does not exempt the other foods. The Even HaOzer (174) disputes this position, as does the Shulchan Arukh HaRav, who maintains that R’ Chiya is at least partially accepted.

The Biur Halakhah (174) asserts that wine only exempts other liquids when it is drunk “b’k’viut”; but a small taste will not due it. However, as R. Fisher observes, if it is assumed that R’ Chiya is accepted in regards to wine (as is the view of the Pri Megadim, against Tosafot, Berakhot 41b, s.v. v‘yayin), this position could be disputed; as long as the berakhah on wine is recited, it would exempt other liquids.

Similarly, R. Fisher disputes a ruling of the Tzlach (to Berakhot) that maintains that wine only exempts other liquids when the wine consumption is ongoing; once that process has ended, the coverage would end with it.