Chapter 49: 7-9
The Blessings for Wine7. When one is dining with others, before reciting the blessing borey pri hagofen in the middle of a meal, one should announce savri rabbonon - i.e. pay heed and hear - so they will stop eating and listen to the blessing.*
* {The Misgeres Hashulchon (9) and the Mishnoh B'rurah 174:46 state that this applies only when the others intend to fulfill their obligation by reciting "Amen" to his blessing.}
8. If people were drinking one type of wine - whether in the midst of a meal or not - and another type of wine was brought to them, they should not recite borey pri hagofen, over it, because they have not changed their minds or diverted their attention from drinking wine. However, they should recite the blessing hatov v'hameitiv - who is good and who does good.
Similarly, if a third type of wine is brought before them, they should also recite hatov v'hameitiv upon it. The same rule applies if many [different types of wine are subsequently brought to the table]. ([The Jerusalem Talmud, Berochos 6:8 relates] that Rabbi Yehudah Hanosi would recite the blessing hatov v'hameitiv for every barrel of wine he would open.)
9. If a person actually changed his mind [i.e., he had ceased drinking wine and now decided to drink again] to the extent that he is required to recite borey pri hagofen (See Chapter 57), he should first recite the blessing hatov v'hameitiv is recited before drinking it.