In the same way that Americans speak of flours in terms of their protein content, Europeans speak of ash content. But what is this mysterious “ash” and why would you want it in your flour? The answer is that the ash isn’t in the flour, it what’s left over after a set quantity of flour (100 grams, I think) is burned — burned in such a way that the starch burns up almost entirely. What’s left are mostly minerals.
So what does this minerally “ash” tell you? More than you’d think. If you consider a wheat berry in the same way you would an onion: a thing made up of many layers. The layers on the outside are the tougher ones that contain less of the starch than the much purer inner layers.
Bleaching gets a very bad rap these days. It’s frequently portrayed as a trivial cosmetic process that comes at the steep cost of adding chemicals — chemicals! — to our food. More than that it could be racist. But in fact bleaching is not primarily about a flour’s whiteness, it’s about a flour’s performance.
But first what exactly is “bleaching”? In general, bleaching means exposing flour to a compound like chlorine gas, ascorbic acid (vitamin C) or perhaps an enzyme like lipoxygenase (derived from fava or soy beans). These agents leave no residues or residual flavors, nor do they, contrary to popular myth, diminish the flour’s nutritional value.
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: how hard or soft the wheat that it came from, how well it will perform in a cake or a bread, how chewy or tender your finished product will be, and so on.
Europeans gemerally do not talk this way. When they talk flour, they speak of “ash content“, which is also a highly descriptive measure, just very different from 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’s nice, but it’s an advantage that comes with some disadvantages as well. If you’ve ever eaten a French blueberry muffin, you know what I’m talking about.
This applies only to North America I need to emphasize, and really most of this information isn’t terribly relevant to home bakers, but you know I like to be thorough. So here goes.
You’ll perhaps remember from the below post the “fairly coarse, fairly dark” flour you get when you grind the whole endosperm of a wheat berry with the bran and germ removed? Well that’s what we in the States call “straight” flour. We generally don’t bake with it, we sift it, though the French frequently use it for bread flour. Just another reason why replicating French breads in the US is difficult.
And how does that impact the “whiteness” of the flour? That’s what reader Leslie is curious about today. Leslie, it’s a good question. Indeed I’ve received quite a few technical questions about flour since Friday’s post on white bread. My thinking is that I’ll put together a few posts on flour and make a “flour primer” out of them for the ingredients section, since I don’t really have one of those yet.
So then, to answer. The “extraction rate” of a flour is a good indicator of its softness and whiteness, as it measures how much of the total wheat berry the flour contains. The higher the extraction rate, the more of the bran, germ and tougher outer layers of endosperm the flour has in it. A whole wheat flour is by definition 100% extraction, since it contains all the parts of the wheat berry.
The majority of the flour we consume is made from a single species of wheat: Triticum aestivum, also called “bread wheat” or “common wheat”. It’s a species that’s been cultivated for hundreds of years, and like all crops that have been widely grown over long periods, different forms of it have evolved and/or been created over time. Nowadays we grow many different types of T. aestivum, all with different properties.
In America our most common wheats are Hard Red Spring Wheat, Hard Red Winter Wheat, Soft Red Wheat, Hard White Wheat and Soft White Wheat. All are used, sometimes alone but usually in combination, to make the flours we find on grocery store shelves. Of the varieties, the hard wheats make up about three quarters of the annual harvest in the US, soft wheats about 20%, and oddballs like club wheat and durum (both of which are different species of wheat, and are used for cake flour and pasta respectively) make up the rest.