Wheat
Wheat kernels which never came in contact with water – and they usually have not – are not chometz. [Wheat with an Eida Chareidis hechsher is not rinsed with water (מדריך הכשרות ).]
Barley, pearl barley
It is common for barley to be rinsed in water. [Barley with an Eida Chareidis hechsher is not rinsed in water and is not chometz (מדריך הכשרות ).]
Oats and oatmeal
Oats and oatmeal come in contact with water and are actual chometz.
Rye
Rye generally has come in contact with water.
Regular flour
Before wheat kernels are ground into flour, they are usually sprinkled with some water to make them easier to grind, but they do not usually split in such a small amount of water and such a short time. Thus, strictly speaking this flour is not actual chometz. However, out of concern that the kernels did split, it is advisable to treat flour as possible chometz and include it in a chometz sale to a non-Jew. Even those who are machmir not to sell actual chometz can be meikel to sell regular flour (הגר''ש וואזנר, מכירת חמץ כהלכתו פ''ד הע' ב'). Still, if one only has a small, insignificant amount of flour, it is advisable to dispose of before Pesach.
Dry flour
It is possible to purchase “dry flour” that did not come in contact with water before it was ground. If one has this before Pesach, he can lechatchila include it in a chometz sale even if he is machmir not to sell actual chometz. It is worthwhile to note that Eida Chareidis products after Pesach that say “ground after Pesach” are often made after Pesach with dry flour that was ground before Pesach since it has no concern of chometz (מכתב של וועד הכשרות דה''ש , Chukai Chaim 88, paragraph 48).
