One thing about 18 month olds, they are consistent! They all seem to throw food off their trays at this age. I think it has to do with their "out of sight, out of mind" way of thinking. "If I can't see it, it doesn't exist!"
I finally figured out that I needed to do meals in "courses." First course was what they really needed to eat--vegies, fruit, meat, etc. Then the filler stuff (cereal, cracker,etc.) Then milk. That way they would except the stuff they didn't like because they were hungry. Stuff still ended up on the floor, but it was easier to pick it up because it was cereal or something dry.
I had one that I would mix food together for and he learned before he was one to manipulate it in his mouth, swallow what he liked and maybe an hour later, spit out the peas. It was amazing!