Good morning, friends and neighbors!
So in addition to being an amazing piano teacher and partner, my wife Emily also tends to act as my editor. She doesn’t just proofread my work, but tests it for readability. IS what I’m writing actually coming across? IS the blog post actually meeting it’s purpose?
Sometimes this comes out by her asking follow-up questions. While she was reading through last week’s post on yeast and fermentation, she got to the part about the different sugars and starches present in wheat.
“Why does the yeast have trouble with starches?
“Why isn’t there enough alpha amylase in the wheat, and why does malted grain provide it?
“Is this why there are different kinds of flour? What’s the difference between bleached/unbleached/enriched/bread flour/pastry/cake/all purpose? Hey, you should write a blog about that!”
So this week, let’s do a deep dive on the science of flour!
Kernels of Truth
For the purposes of this post, when I say “flour,” I’m referring to wheat flour– that is, the pulverized and sifted seed of the common wheat plant (triticum aestivum.) Depending on the type of flour desired, different parts of the wheat kernel get sifted out (or left in.)
While milling other grains and seeds to make flour is common (einkorn, amaranth, millet, spelt, rye, etc), wheat flour is the most popular for its nutty flavor and gluten content.
What’s the Deal With Gluten?
Before anyone starts getting sweaty about eeeeeeevil gluten… let’s talk for a minute about exactly what it is, and why some people might have an issue with it.
Wheat contains two particular vegetable proteins- glutenin and gliadin. By combining the wheat with water and mixing (i.e. making bread dough,) these proteins combine Captain Planet-style and form gluten. In order to encourage/discourage/strengthen/weaken gluten formation, modern mills add a host of additives to their flour.
Gluten looks and acts like a coiled spring, or an old spiral telephone cord. It is elastic and stretchy- to a point- and as it gets worked on (by kneading and mixing, for example) it gets tougher and stronger. After being baked, gluten is the main substance responsible for the structure of bread. This is why gluten-free baked goods tend to be crumbly- unless they use a mixture of additives (like xanthan gum) to replicate that gluten, there’s not much holding those brownies and cakes together.
For about 1% of people, consuming food with gluten can cause an autoimmune reaction where the body attacks the nutrient-gathering villi in the small intestine, called celiac disease. The result of this can lead to bloating and diarrhea in the short term, and intestinal damage, cancers, and a host of other health issues long term. The existence of “non-celiac gluten sensitivity” are still currently being debated, but the immediate symptoms are generally the same.
As of right now, the only treatments are a strict gluten-free diet. Look, I work in the food industry. I’m a goddamn BAKER. I KNOW that “gluten free” and “food allergies” (discussed in air quotes) are the popular whipping boy in some professional circles, and that preparing special food for customers or maintaining allergen-free tools and spaces is a pain… but there’s a reason for it. This stuff is NOT. MADE. UP.
TAKE IT SERIOUSLY.
Enriched for Function, Bleached For Looks
For coming from a single kind of plant, there is a LOT of variability in wheat- the hardness/softness of the kernel, the season it was grown, the color. I’m going to skip most of that here and focus on the elements that most directly impact your baking-
- Starch content
- Protein content
- Additives if present (spoiler alert: THERE ARE.)
Why are additives used? Simply put, because milling flour makes it suck.
Check out this diagram of a wheat kernel. It’s got three main parts- the bran, the endosperm, and the germ. Most flour JUST uses the endosperm and germ since that’s where all the protein and starch is- the bran contains most of the actual nutrients in wheat as well as the dietary fiber. It also, unfortunately, contains other stuff that hampers gluten production. It’s why many recipes that use “whole wheat” flour (flour that includes the bran) will often require some added regular flour.
If you’re getting rid of all the nutrients from the wheat by making it into flour, but you don’t want people to come down with nutritional deficiencies (or the diseases that come from them,) you need to add the nutrients back in artificially. Here in North America, flours that get this treatment are called “enriched” since the early 40s, when it was discovered that treating grain foods with niacin stopped seasonal outbreaks of pellagra.
Besides nutrition, mills will often add substances to flour or process it for cosmetic and performance reasons.
- Bleaching Agents– because folks like their flour (and bread) as white as possible. In addition to whitening flour, some agents (such as chlorine) weaken gluten, making those flours “soft”, and ideal for cake flour. Benzoyl peroxide is also used, but it doesn’t interfere with gluten.
- Maturing/Conditioning Agents– If you need to make a hard flour softer, or a soft flour harder, “dough conditioners” can be added either by the mill OR by the bakers themselves. A former favorite conditioner was potassium bromate, which strengthened gluten… but was also found to be a carcinogen. Illegal in the UK and Canada, it’s still used in the United States, though it’s falling out of style in favor of the healthier-but-less-efficient ascorbic acid, a.k.a. Vitamin C.
- Aging– If you want to avoid adding a bunch of stuff to your flour, the answer just seems to be giving it time. Naturally aging flour by oxidizing it (by… well, just exposing it to air) bleaches the wheat on its own, and the oxygenation strengthens gluten as well. Unfortunately, you’re going to wind up paying a bit more for naturally aged (or “unbleached,” as it says on the bag) flour, since the process can take a while and increases the possibility of the flour molding or getting pests in it. The flour also won’t be quite as reliable as the chemically-altered stuff.
A Flour for Everyone And Everything
Now for the big question everyone wants to know… what’s the difference between all those flours on the shelf?!
This is “hard” flour, with a comparatively hefty amount of protein and gluten in it. This is meant for baked goods that need sturdy structure- that need to stretch and bend before they tear. For obvious reasons, it’s also called “high gluten” flour.
A step softer, this is often made with “soft wheat.” It has less protein and also less starches to absorb water, making it ideal for any baking where you want the batter or dough more fluid and the product less dense, like cakes and thin cookies.
All-purpose (or AP) flour is a mix of pastry and bread flours that isn’t really used by professionals. As the name implies, it’s balanced to do more things “okay enough” rather than any particular baked good “well.” That’s what makes it ideal for the home cook who DOESN’T want five different bags of flour in their pantry.
Speaking as a professional… this stuff weirds me out. Cake flour is made from the smallest, tenderest parts of the kernel, and then is bleached with chlorine until it’s white as the driven snow. All that chlorine weakens the ability to make gluten so much that all there is to absorb any liquid is starch. If you want crumbly cookies that keep their shape perfectly and don’t brown, or a fluffy cake that falls apart on your fork, this is the flour you want.
In almost any kind of baking, flour is the major ingredient. Changing that flour will alter the chemistry of your recipe, the structure of it… everything from the flavor to the appearance of the final product. If you are using flour in a non-baking recipe (dredging chicken breading, browning meat for a stew, making a roux, etc), it doesn’t matter that much. In those instances, flour is just being used as a convenient binder, thickening, or drying agent.
That said, I need to tell you that in researching for this blog, I was surprised to learn that the only flour you can’t come up with a substitute for… is all-purpose flour!
According to the nth-level food wizards at Cooks Illustrated, bread and cake flours can very easily be substituted in for all-purpose. It won’t be utterly perfect, though. Because of the different protein content, recipes that are meant to have bread flour in them will be a little softer and less chewy, while recipes for cake flour will be a little firmer and less white.
If you’re out of all-purpose though… better hope the store is still open.
Anything else you want to know? Anything I missed or got wrong? Drop it in the comments!
If you really want to nerd out about the science of baking, I recommend “How Baking Works” by Paula Figoni. It was as huge a resource for me in writing this blog post as it was back in school (where it was essentially the culinary school equivalent of a chemistry textbook.)