Berachot 50: The Importance of Bread, Splitting or Joining Two Groups

Briefly:

If we have a group of at least ten people in a zimmun, we do not wish to split the prayers to stay Grace after Meals.  If we do that, we cannot invokes G-d name, and it is a privilege to invoke G-d's name.  Even if we have fewer than ten people together, they can be split into smaller groups to bench, for non of those groups will invoke him.  An interesting aside.

Wwe learn about bread and wine. Four things that we learn about respect for bread:

• we cannot let bread be ruined by the blood from raw meat
• we cannot let bread be ruined by wine that has spilled
• we cannot throw bread
• we cannot use a plate to hold up bread

Bread is associated with our corporeal wellness and our groundedness.  Indeed, we bless "bread from the earth".  It is essential.  The rules about suggest that bread cannot be made unkosher, unappetizing, or treated irreverently.  

A new Mishna teaches that three, four or five people who eat together are not permitted to divide and recite Grace after Meals individually.  If the group is between six and ten people, they can be split into two groups, each reciting its own zimmun.  Between ten and twenty men cannot split up because both groups would have to say exactly the same zimmun.  As long as the members of two groups can see each other, they are permitted to join groups together.  Further, Rabbi Eliezer says that water is added to wine before the wine is blessed.  This is because undiluted wine is not appetizing.

We learn that what is blessed is intended to be both equitable and pleasant.