This section is from the book "A Treatise On Flour, Yeast, Fermentation And Baking Together With RecipesFor Bread And Cakes", by Julius Emil Wihlfahrt. Also available from Amazon: A treatise on flour, yeast, fermentation and baking, together with recipes for bread and cakes.
The value of flour, of course, depends upon the quality and quantity of gluten it possesses, and also upon that substance from the soil, which, in the analyzation of the soil and in the investigation into the growing grain, is known as protein. The gluten itself consists of two distinct parts, namely glutenin and gliadin. In fact, there is no such thing as gluten in the flour; but by making flour into dough, the two combine. Gliadin is of a sticky nature, something like gum, and adheres to the glutenin during the process of bread-making. The glutenin, in its natural state, is of a dry, granular consistency; the two combined form gluten.
In this form it is obtained by washing flour with water. The quality of flour varies in proportion to the amount of gliadin in the gluten, up to a certain limit. Patent flour, compared with Spring clear flour, shows gliadin of approximately 70% of the gluten in the patent flour and 60% in the straight Spring flour. In other flours, the gliadin rises as high as 80%; 70% of gliadin is the limit or ideal mark, and a flour containing more than this percentage of gliadin is apt to produce a sticky dough.
In other terms, the value of a flour, or consequently its gluten, first depends upon the quality of such gluten, which means the right proportion of glutenin and gliadin, and the quantity of gluten contained is only to be considered as a second factor, it is of much less value than quality.