
fermento – verb meaning to leaven, to cause fermentation
immolo - verb meaning to immolate, to sacrifice
These words help us understand why the offering at the Holy Sacrifice of the Mass is unleavened bread. It looks flat.
After the killing of the first born, Pharaoh agreed to let the Israelites go, but to leave Egypt quickly, the Israelites could not let their bread rise, and so they brought unleavened bread with them. Thus, the Jewish Passover is celebrated with unleavened bread. However, Catholics celebrate with the new unleavened bread, not the old, because Christ Himself is now the bread and truly present.
“More than one flour is used. White hosts are a mix of pastry and cake flour. [Cake flour is milled from soft wheat.] As Sister Mary Angela explained, ‘The pastry is heavier and the cake flour much finer and bleached. This mix prevents hosts breaking and falling apart. All-pastry flour would make the host look yellow, too. It needs both kinds.’ White hosts should look white, but whole-wheat hosts are not white. Still, the whole wheat is mixed with some white flour because two different flours are always necessary to prevent hosts from breaking and falling apart.”
https://www.ncregister.com/features/the-bread-of-heaven-where-do-communion-hosts-come-from
There is also tremendous practicality in using unleavened bread. The possibility of particles, or crumbs, falling about is greatly reduced. The priest is fastidious in handling the consecrated bread at the altar, and altar boys hold a communion-plate, patina in Latin, to catch any falling particles.
copyright 1936 Benziger Brothers