Plain flour is the same as all-purpose flour. It is an combination of hard and soft wheat and generally contains 8 to 11 percent wheat protein or gluten.
All-purpose flour can be bleached or unbleached and each kind is used for different purposes. Bleached flour has been chemically treated to appear white and is best used for pancakes, waffles, breads, cookies and pie crusts. Unbleached flour is allowed to lighten naturally with age and is best used for pastries and turnovers. Both types of all-purpose flour last up to a year with refrigeration and about eight months if tightly sealed and stored in a cabinet.