Berachot 39: How Much Food Must be Eaten for Blessing/Punishment, Breaking Bread

When we eat food that is prohibited by Torah or rabbinic law, we must eat at least a medium olive bulk (or one-half or one-third of an egg bulk, say some) to meet the requirement for punishment.  When we eat a food required by Torah, we must eat at least one-half of an egg bulk.  Steinsaltz gives the example of eating matzah on Pesach.  When we eat a food required by rabbinic law, for example, parsley on Pesach at the seder table, we must eat at least one-third of an egg bulk.

We have learned that we bless first what is more specific and thus more significant when we are eating more than one food at once.  A story is told of two students, one who hurriedly recites the wrong blessing first to eat his preferred food and the second who ridicules the first.  Bar Kapara is angry with both of them for their transgressions and it is said that neither of them lived through the year.  

The rabbis have a long conversation about the health benefits or dangers of different foods, mostly vegetables.  Some are considered to be more nutritious and thus more worthy of blessing and eating first.  The largest, most nourishing, most valuable, most tasty vegetable takes precedence both in blessing and in separating teruma, tithes for the priests.

The end of our daf is devoted to a discussion about breaking bread, particularly on Shabbat, but also on ordinary days and during Pesach when we break matzah.  The rabbis share their very different traditions regarding when one should recite the blessing versus when one breaks bread.  Further, they describe how the two loaves on Shabbat should be lifted, how they might be adjusted, whether one or both should be cut, whether a large or small piece should be taken, and other related questions.  Every opinion is shared with relevant proof texts or minhagim, customs.