Here in the States we’re used to talking about flours in terms of how much gluten (protein) they contain. Know the gluten percentage of a given flour and you know a fair amount about it: the hardness or softness of the wheat it came from, how it will perform in a cake or a bread, how chewy or tender your finished product will be, and so on.
Europeans generally do not talk this way. When they talk flour, they speak of “ash content“, which is also a highly descriptive measure, but it says nothing specific about gluten content. And while we’re on the subject of Europe, I should point out that European gluten is very different from North American gluten. While ours is stretchy and elastic, theirs is firm and plastic, meaning it doesn’t “snap back” like ours does when it’s stretched. That can be a very good thing, but it can be a disadvantage as well. If you’ve ever eaten a French blueberry muffin, you know what I’m talking about.
American flours have a gluten percentage that’s right around 10%. That’s about standard for an all-purpose flour. A few percentage points less and you’re into cake flour territory, a few percentage points more and you’ve got some serious bread flour on your hands.
But what determines how much gluten a flour has? There are two primary factors: the type of wheat the flour was made from and the extraction rate (more on that below). Hard red wheats, which tend to grow in the northern regions of the North American continent, are generally high in gluten. They make great bread. Soft red wheats, which tend to grow best in warmer Southern climates, are low in gluten and are generally better for things like biscuits, crackers, and cakes.
But of course the way that wheat is milled also has an impact. As I mentioned below in the post on extraction rates, it’s the outer layers of the wheat endosperm (starch reserve) that have the most protein. Thus a high extraction flour is going to have more protein regardless of the type of wheat it came from, and a low extraction will have less.
Here it’s important to note that gluten, American or European, can vary in quality. Low quality gluten will tend to break down over time. So if, say, you were making a hearth bread that needed to ferment for many hours or even days, the gluten molecules themselves would begin coming apart. The effect being a lower-volume, even collapsed loaf of bread.