Hard Red Winter Wheat:
This wheat is mostly grown in the Great Plain states and Canada and is moderately high in protein, which makes it good as an all purpose bread flour. About 40% of all wheat grown in the USA is Hard Red Winter Wheat.
Hard Red Spring Wheat:
Wheat Montana's "Bronze Chief" flour and wheat berries are this variety of wheat. It is considered the "aristocrat" of wheat when it comes to wheat foods like hearth breads, rolls, croissants, bagels, and pizza crusts. It is one of the hardest wheats, and therefore has one of the highest protein counts. It makes up about 24% of the wheat grown in the USA.
Soft Red Winter Wheat:
This wheat is mainly grown in the Eastern states and has a low protien count. It has excellent milling and baking characteristics for pan bread and general purpose flour, and makes up approximately 25% of US grown wheat.
Hard White Winter Wheat:
This wheat is sweeter and lighter in color than the red wheat varities, with a protein profile similar to Hard Red Winter Wheat. Only a small percentage of the wheat grown in the USA is Hard White Winter Wheat, but it is beginning to gain popularity.
Soft White Spring Wheat:
This is generally grown in a few eastern states and the Pacific Northwest and California. It is a low moisture wheat with high extraction rates that provides a whiter product for cakes and pastries. Similar to Soft Red Winter Wheat with a slightly sweeter flavor. It makes up about 7% of all USA grown wheat.
Hard White Spring Wheat:
A newer class of wheat marketed in the United States, but not in other places throughout the world. This wheat is favored for its creamy light color when ground as whole grain flour. Hard White Spring Wheat has a high protein count and strong gluten for bread baking. "Prairie Gold" wheat from Wheat Montana is this type of wheat. If you recieved a free bag of wheat berries with your GrainMaker Mill, it was "Prairie Gold" wheat.
Hopefully you have found this information helpful. Of course, you will want to experiment with the different varieties (and maybe mix a few!) to find out which makes the flour you like best. Happy grinding!