Leviticus 2:11 (ESV)
11 “No grain offering that you bring to the LORD shall be made with leaven, for you shall burn no leaven nor any honey as a food offering to the LORD.
The use of leaven was forbidden at the Passover (Exodus 12:15; Exodus 13:3, Exodus 13:7) and with sacrifices (Exodus 23:18; Exodus 34:25). Some have suggested that yeast is often used as a symbol for corruption. This is the reason why it should not form a part of this offering. It must be remembered that the use of yeast was not prohibited in all types of grain offerings, but for most of them (see Leviticus 7:13; Leviticus 23:17).
4 “When you bring a grain offering baked in the oven as an offering, it shall be unleavened loaves of fine flour mixed with oil or unleavened wafers smeared with oil.