Wheat is the world's most important grain crop.  Wheat is important not only for its nutritional value, but also for its gluten content.  Gluten is the protein of the wheat which, when properly developed by kneading, will trap and hold the yeast gas in the bread dough causing the bread to rise.  Wheat is the only grain with the proper amount of gluten to facilitate the rising of bread dough to make light, soft loaves.There are two basic categories of wheat, hard wheat and soft wheat. 

Hard wheat is grown in cool, dry climates, either in the winter or the spring.  Dry winters and springs make the protein, or gluten, content high, and the moisture content low.  A high gluten content is necessary to make yeast breads.  Hard wheat is named for the season it is grown (i.e. hard winter wheat or hard spring wheat).