“Extraction rate” sounds like a technical term. Which it is. Though that’s not to say that home bakers like you and I can’t understand it and use it. Particularly if you like to bake bread, an extraction rate can give you a good deal of information about a flour, as well as several clues about how it will behave.
So, to business. When someone uses an extraction rate in a sentence, say, “this is a 65% extraction flour”, at least two important types of information are being conveyed. The first is the region of the wheat berry where the flour has been taken from. The second is the composition of the flour, i.e., how much of the softer inner endosperm, harder outer endosperm, and even bran and germ the flour contains. And when you know all that, you also have a sense for how much gluten (protein) the flour contains, even the grind of it. It’s one pretty darn info-packed number.
To make sense sense of an extraction rate, it helps to think of a wheat berry as an onion. On the very outside is the skin: the bran. Beneath the bran is the starchy endosperm. Most people think of wheat endosperm as a uniform piece of starch, but that isn’t true. The endosperm is actually comprised of layers, each of which differs somewhat in composition and texture. The very outer layers, for instance, are the hardest, least uniform part of the endosperm. These layers are brownish-white, having a fair bit of bran still in them, as well as a good deal of the wheat berry’s nutrients, and a high proportion of the berry’s protein (gluten). Progressing inward toward the center of the wheat berry, the endosperm layers get more uniformly starchy and softer, until you get to the very center of the berry where they’re almost completely pure, white-to-yellow starch.
Knowing that, we can get back to what this post is about: extraction rate. In the most literal sense, an extraction rate can be taken to mean: “this is how much flour I got when I took my sack of wheat berries to the mill for grinding”. If 100% of what was in your sack was handed back to you as flour from the mill, then you have a 100% extraction flour. It contains every bit of the endosperm, hard and soft layers, as well as all the wheat bran and the wheat germ (the wheat embryo that’s attached the end of the berry). That 100% extraction flour is — you guessed it — whole wheat flour.
But what if the mill started taking away pieces of the wheat berry? Like the germ, the bran, and some of the outer endosperm layers? In that case you’d be getting back less than 100% of what you gave them. Your flour would therefore be a lower extraction rate flour. Its composition (and by extension its performance) would also be different.
So let’s say they started by removing the bran and the germ from the berry, as is typical when wheat first comes into a mill, then ground what was left into flour. The bran covering makes up about 12% of the wheat berry, and the germ another 3% or so. Add that together and you have 15%. Take that away from your 100% extraction flour and you have 85% of the total berry. Grind it and the result is an 85% extraction flour, which is still a pretty stout item, since it has all the outer protein-rich endosperm in it and some residual bran as well.
But let’s say we took that harder outer endosperm away. Those layers make up about another 15% of the wheat berry. Remove them, grind what’s left and you have 70% extraction flour. This is a down-the-middle sort of flour, not too hard, but not too soft either, good for lots of things. Which is why most all-purpose (AP) flour is about a 70% extraction flour.
As we keep stripping layers away, heading toward the center of the wheat berry, we get purer and purer starch, until we get to the very middle third of the berry. This is the softest inner endosperm, lightest in color, and containing the least amount of the protein and nutrients. Ground, this ultra-low, 33% extraction flour is great for cakes and pastries.
So you see how all this extraction-rate stuff works, yes? And why it isn’t just a term for in-the-know bread heads. Much can be gleaned from just this one humble little number. You can even infer the fineness of the flour’s grind by the extraction rate, since lower extraction flours tend to be a finer grind and higher extractions coarser. This isn’t a hard-and-fast rule, mind you, as there are a lot of very find whole wheat flours on the market these days, but it works as a rule of thumb.
Of course an extraction rate won’t tell you everything. It won’t tell you what type of wheat the flour was made from, for instance, and that can be important when you’re trying to decide what kind of flour to use for what application. Flour made from hard north American wheat, for example, isn’t ideal for Southern biscuits no matter how low the extraction. Still, I hope this helps clear up a topic that, for many, has become highly confusing.