What is “Ash Content”?

First let’s get a show of hands. How many people here have had someone brow-beat them with the term “ash content”? Come on, don’t be shy. There’s no shame in it. Put’em up. Yep, I thought so. There’s a certain type of bread head out there that simply loves to do that. But let me tell you, there’s nothing about ash content that’s hard to understand. Once you have a general sense for what it means, you’ll be able to go toe-to-toe with even the most heavily-tatted, ringed-and-plugged artisan bread bakers. Just don’t go making fun of the bleak industrial Throbbing Gristle and Mica Levi records they listen to. I won’t be able to help you in that instance.

But what exactly is “ash” and why do you find it in European flour? The answer is that there actually is no “ash” in European flour. Europeans use the term “ash” as a catch-all term for everything in their flour that is not pure wheat starch. Things like bran, germ, protein, minerals and other nutrients. The higher the “ash” content, the more of those kinds of things you find in the flour.

With me so far? The reason it’s called “ash” is because long ago, Europeans developed a method for testing the relative purity of their flour, and they did this by burning it. They found that when you burn flour at a very high temperature, the starch — being made of sugar and therefore very fuel-like — burns away totally, leaving a residue composed of…well, everything else. So when someone tells you that this particular French flour has an ash content of 0.65%, all it means is that when a particular miller burned 10 grams of this flour, they were left with 0.065 grams of ash.

“So what does that have to do with the price of avocado toast in Portland?” you may ask. Well I’ll tell you. Knowing the ash content of a European flour is exactly like knowing the extraction rate of an American or British flour. That one number, by telling you how pure or impure the flour is, tells you by extension how much gluten (protein) the flour has, and how much bran or germ it has. And if you know those things then you have a pretty good idea for how the bread will perform when you bake with it. You even have a sense for what the grind will be.

More on this when I talk about the various kinds of international flours. Meantime, to get a more complete understanding of this subject, I strongly recommend reading the extraction rate post I linked to above. Keep developing those brain muscles, friends — and never let a hipster bread head kick bran in your face again!

4 thoughts on “What is “Ash Content”?”

  1. Dear Joe,
    It is not easy to live in Europe while being a fan of Rose. After 5 years of living in Germany, I still struggle with finding and understanding the “Typ” of flour. Typ 405 is stated to be close to pastry flour, while Typ 550 is the cousin of all-purpose flour. However, I do think that the Typ of flour is also called different in some cookbooks, which are published in the USA but written by french authors. Sometimes they call Typ 405 all-purpose and T550 bread flour.
    I wonder if you have done some research about it and if you can help me answer this question.
    P/s: I’m not a frequent visitor to your blog, but I have even though read many articles from your blog. I did have a thought that you stopped blogging years ago. Surprisingly, you’re still here, still providing us helpful pieces of information with your researches.
    I hope that you will keep blogging without regarding how many people actually visit your blog everyday. Reading this post makes me feel happy as if I met my old friend. I’m sure that your posts are gems, or at least “a small piece of cheerfulness” for people who randomly visit your blog again after a long absence.

    1. Hello Colleen!

      If you are a fan of Rose, then you must be trying to make layer cakes, correct? Tell me what is happening to your cakes and I can be more helpful.

      In the meantime, I can tell you that yes, German 405 is the closest to American pastry flour, and 550 is the closest to all-purpose. However there are differences in they way they perform because the types of wheat used are different.

      And thank you for the kind words! Please come back any time!

      Your old friend,


  2. Dear Joe,
    Rose does have a post about “Power of flour”. Cake flour in the USA is bleached, which makes the starch granuales more rough and able to hold fat and liquid (in other words: creating emulsion). She also give another option beside bleached cake flour (which is prohibited in Europe) and Kate’s Flour (she said that the “bleaching” process by using heat does give the nutty background for the cake): adding potato starch. I think this is an european technique, because many tradition and french recipes call for potato starch and not cornstarch. However, the flour still cannot support the structure of the cake, which often results a thick dense layer at the bottom of the cake. The cake rise well in the oven, as if you have done it properly; but it deflates significantly after a few minutes.
    Surprisingly this only happens when I make the cake using soften butter. If I use oil or melted butter, the cake doesn’t have the problem mentioned above.
    I found that German Typ 405 has strange characters: when you making pastry (using Rose’s recipe), you always have to add more water or cream (or liquid); but this type of flour isn’t strong enough to make bread. The protein content also varies from 10% to 12%, which is more than German Typ 550 with 11% Protein.

    I hope that I provided you some helpful info.

    Best regards,

    1. Thank you again, Colleen! That’s very interesting. I’m not too surprised that melted or liquid fat performs better for you. American-style cake layers depend on a very thorough distribution of fat. Liquid or melted fat would allow for that very even distribution, and help to create the very fine structure that allows the cake to stand.

      You have clearly done a good deal of excellent work on this subject. You cleary like cake! 😉

      I very much appreciate your insights!



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