The custom today is to make a bonfire of your leftover chametz on the morning before Pesach. This is based on a biblical commandment to “remove leaven from your houses”. The Talmud states that “removing leaven” according to the Torah is simply declaring all your chametz null and void (Pesachim 4b). The sages add to this the command of biur, the physical destruction of, chametz.
Rabbi Yehudah says that burning chametz is the way to do it. However, the sages say that you can crush your chametz and cast it out to the sea (or, these days, down the loo.) They believed the important aspect of biur chametz is a chametz-free home, but Rabbi Yehudah that destroying the chametz is an important act in itself. Halachic authorities have split on this issue. The Shulchan Arch rules that you may dispose of your chametz in any manner. The Rama states that it is customary to burn it.