470. Beginning Hilchos Brachos

Brachos 1:1

There is a positive mitzvah in the Torah to bless God after eating and being satisfied, as per Deuteronomy 8:10, “When you have eaten and are satisfied, you shall bless Hashem, your God.” The Torah only requires a person to bentch (recite grace after meals) when he has eaten enough that he is satisfied but the Sages instituted that we should bentch after eating an olive-sized portion of bread.

Brachos 1:2

The Sages also instituted that we recite brachos (blessings) before partaking of any food or beverage, even the smallest amount. Similarly, one should recite a bracha when smelling a pleasant fragrance. One who derives benefit from the world without reciting a bracha is considered like one who misappropriated sanctified goods. The Sages further instituted that a person recite a bracha after eating an olive-sized portion or drinking a reviis (about 3.5 ounces). One who only tastes food need not recite a bracha, neither before partaking nor after, unless he has a reviis of it.