"leaven"

“Leaven” – not to eat during Unleavened Bread – (Biblically Kosher by Aaron Eby)

Sh’mot (Exodus) 12:15 – Three terms in this verse:

Matzah – translated “unleavened bread”

Se’or – translated “leaven”

Chametz – translated “what is leavened” or “leavened bread”

-      These translations can be misleading…”The Hebrew terms do not refer to “leaven” or “leavening” in the sense that we use the word today.” 

Chametz – refers to products made of certain kinds of grain/s that have come in contact with water and are allowed to sit for a period of time before being cooked. – Not just fluffy bread, but noodles, cookies, drinks.

Se’or - refers to an inedible lump of starter dough that contains a high concentration of yeast.  Yeast itself is not chametz or se’or.

Matzah is flat bread that is made with flour and water and baked quickly at high temperatures.  This ends the biochemical processes that would otherwise make it chametz.

What NOT to eat …

Wheat, barley, oats, spelt, rye.

Vinegar – unless pure wine vinegar… or things with grain vinegar in them like mustard, ketchup, mayonnaise.

Beer.

All baked goods with the above grains in them, pastas, crackers, flour tortillas, pretzels  etc…

This is not definitive but a basic list.