What is the difference between flour types?
An ode to flour
Flour is a truly amazing substance. It starts off as a simple powder. But as soon as you add water, it turns into an interconnected web of sticky fingers. As you keep mixing it, it becomes less sticky and stiffer to move. Eventually, this gooey mass takes upon shape, is formed into a loaf, and baked in the oven. And out comes out a delicacy full of so many complimenting flavors and delicate texture that is somehow unimaginable to have originated in nothing more basic than this fine dust and water.
History of baking bread
People have been baking breads for thousands of years. First breads were unleavened – flat breads that were produced by mixing flour with water, flattening the resulting paste down to a disc, and placing it on a flat plate preheated in a fire pit. Only with time did people discover the delicacy of leavened (fermented) breads. The first leavened breads were probably accidents: leavening is produced by yeast, small fungal microorganisms that are present in the environment all around us. Leave some flour out uncovered for few days and it starts fermenting. The same is true with brewing beer. These wild yeasts come from different subspecies and every type produces different flavor chemicals. Some are tastier than others, and only through selective process of reusing old bread and saved dough pieces as starters, have people been able to cultivate the delicious bakers and brewers yeast strains now available commercially.
Flour and its constituents
In Slovakia, flour is characterized by the coarseness of the grind. Regular, all-purpose wheat flour comes in three kinds: coarse (hrubá), semi-coarse (polohrubá), and fine (hladká). Here in the US, flour is sold depending on its intended use. There is the all-purpose flour, cake flour and bread flour. These labels indicate the amount of gluten content. Gluten is a protein that makes up only about 30% of flour by weight. However, it is absolutely crucial to baking.
Several different types of flour available in the United States. Clockwise from top left we have rye flour, whole wheat flour, unbleached all-purpose, bleached all-purpose flour, and “instant” Wondra flour.
Gluten are proteins that link together to form long chains. Think of gluten as small jumbled springs. These springs have hooks on both ends, these are amino acids that form sulfur-sulfur bonds with each other. As the flour is wetted, these springs straighten out and start linking together. The more water is added, the easier it is for gluten to form long chains and the more bread-like the finished product will be. With little water you get crumbly cakes. But water is not the only factor controling the gluten strength. Kneading (repeated folding and flattening of dough) helps elongate the gluten chains, as does salt, which helps prevent charged ends of gluten molecules from repelling each other. On the other hand, fats and oils shorten gluten chains by weakening the bonds and so does acidity (as in sour-dough breads), which increases the concentration of positively charged amino acids that repel each other. The amount of gluten in flour is directly affected by the plant from which the flour is made. In the US, most of the wheat crop is so-called hard wheat, which is higher in gluten than soft wheat.
But the main ingredient of flour, by weight, is starch. Starch molecules keep the gluten chains too dispersed to form long chains. This is why cakes, which often contain more sugar than flour, take upon a crumbly appearance. In bread, the starch granules absorb water during baking and form the rigid walls that surround the gas bubbles. Their rigidity helps build up pressure inside the bread, causing the bubbles to pop and find their way out through a maze of interconnected tunnels. In the end, baked bread can be up to 80% empty space by volume. All this empty space is possible thanks to starch providing the structural support. Without the bubbles being able to escape, the bread would collapse after baking finished and the hot steam inside started contracting.
The many kinds of flour
As you may know, I am an engineer. This means I find nerdy stuff like comparing different types of flour very fascinating. So I decided to put all this information to practice and figure out what the difference between different types of flour really is. To study the effect of gluten on the finished product correctly, I should have used high-protein, regular, and low-protein flours, such as bread, all-purpose, and cake, respectively. But not having those in my pantry, I instead used the five different kinds of flour I had laying around: rye, whole-wheat, unbleached all purpose, bleached all purpose, and Wondra®.
I measured out a quarter cup of each. You can see the closeups above. (This experiment was also the first time I got try out my new Nikon D90 DSLR camera). These are sorted by their coarseness and also the amount of refining. Rye flour is not actually made from wheat – it’s made from rye (d’uh!). I don’t know if every type of rye flour is as coarse as this one from Hodgson Mill, but this flour is distinctly different from the wheat flour. If wheat flour is dust, rye flour is sand.
The fines of the grain particles is controlled by the milling process. Milling was such a crucial component of the daily lives of our ancestors, that a mill (mlyn) and the miller (mlynár) appear commonly in traditional Slovak folk tales and traditions. Milling is a process in which the wheat (or rye) kernels are broken up. Flour kernel consists of three components: the outer germ and bran layers surround internal endosperm. It is bran and germ that contain much of the flavor and nutrients, but they also have much shorter shelf life than the gluten-rich endosperm. Hence they are removed from much of the flour sold commercially – this is the all-purpose flour. Germ and endosperm also interfere with formation of strong gluten network. This is why whole-wheat flour, flours in which germ and endosperm are retained, result is somewhat denser, less-fluffy breads than those made from white flour. All-purpose flour is known as biela múka, white flour in Slovak. Whole wheat, on the other hand, is čierna múka, black flour, although whole wheat flour is more yellow than black.
Another distinguishing mark for the many different types of flour is bleaching. Over the centuries of milling, people realized that bread made from freshly milled flour was not as light and fluffy as one made from flour that had been resting for few weeks. So at the turn of 19th century, flour producers started adding various additives to speed up this natural process chemically. After few chemicals with questionably impact on human health, flour producers settled on ascorbic acid (vitamin C). But these additives took care of only one aspect of natural aging. The other one was that, as flour sits around, it becomes whiter in color. This natural whitening is now replaced using bleaching agents such as peroxide.
In my experiment, I used whole wheat flour from King Arthur, unbleached all-purpose flour also from King Arthur, and bleached all-purpose flour from the Giant store brand.
I also used some Wondra® flour. Wondra is an interesting idea. It’s an instant low-protein flour that is produced by precooking flour starch granules until they start to gelate. The flour is then dried. This precooking makes it easier for water to penetrate the starch granules during cooking. This kind of flour is well suited for tender pastries or for thickening of sauces. Consistency-wise, Wondra is very fine, dust like. It is similar to touch to the Slovak hladká múka.
The dough experiment
For the experiment, I transfered each flour into a different cup, and added two tablespoons worth of dissolved yeast. Next I added two “shakes” of salt, and enough water to obtain similar consistency from each flour. The sturdier flours needed two tablespoons, the finer ones, less. I mixed everything together, slightly kneaded it in the mug, and then let the mugs ferment for about an hour.
The difference between the flours was quite apparent. For one, rye flour is nothing like the remaining kinds. When you mix water into rye flour, you end up with a muddy mess that doesn’t strongly adhere to itself the way dough from wheat flour does. What I found surprising was that, despite all this, the rye flour still ended up rising during the fermentation process. There was also quite a big difference between the King Arthur unbleached and the store-brand bleached all-purpose flour. I didn’t sift either, but the King Arthur flour had much fluffier, almost-as-if-sifted, structure to it. It was much easier to work with and the dough was smoother and silkier. The store-brand flour was, on the other hand, quite clumpy.
After the flour has risen, I transferred the content of each cup onto a wooden board dusted with the bleached all-purpose flour, and formed each piece into a small loaf. It wasn’t really possible to form the rye dough, so that one remained in a pancake shape. I baked the pieces together in a 400F oven. Long ago, breads used to baked in ovens made of clay, stone, or bricks. The old ovens were shaped as a beehive, and were preheated by setting a fire in them. The fire was let to burn for hours, after which, the ashes were removed, and bread was placed onto the bottom surface. The thick walls helped retain the heat from the fire – the initial baking temperature was in excess of 700F. The temperature decreased with time as the bread continued to bake. But since the surface also became darker, and hence more absorbing of radiation, the heat transfer to the bread itself did not change that much.
These days, baking is done at much lower temperatures, and in ovens lined with only thin sheets of metal that do not retain heat for long after the heat source is switched off. In addition, gas ovens are vented to prevent build up of poisonous carbon dioxide – along with the steam that releases from the dough. Steam helps to heat the surface of the dough more rapidly – up to four times faster. In addition, steam condensing on the surface of the dough also keeps crust from setting longer, and thus resulting in a larger, fluffier loaf. The dough can expand only until the crust sets. The crust can break if it sets too rapidly before all the gases released during vaporization of alcohols and water in the dough can escape. Water condensing on the surface also gelates starch molecules into a thin film that dries into attractive transparent gloss. This is why home bakers sometimes place ice cubes in the oven with the bread, and why professional bakers have special ovens fitted with steam injectors.
Bread from different types of flour
Well, I didn’t do any of this, I simply baked my experiment for about 20 minutes. There was quite a difference in both the look and the taste of the resulting loaves! Although the doughs were more-or-less the same color before going into the oven, the difference in the finished loaves was spectacular. The rye loaf was dark in color, hearty, and chewy on the inside. It resembled a big, non-sweet chocolate cookie. The whole-wheat loaf had the beautiful crust of the breads I remember from my childhood in Slovakia. This one was also bit chewy on the inside, and could have used another minute or two of baking. The taste of this loaf was the most what I consider bread-like.
There was surprisingly little difference between the three kinds of white flour. Although the King Arthur flour was easier to work with than the Giant brand, the difference in taste of the baked loaves was not noticeable. The unbleached loaf was darker in color than the bleached loaf, but comparable to Wondra. All tasted much like the typical French bread you find in your local supermarket bakery. Even more surprising was that there wasn’t much difference between Wondra and the standard white flours, despite Wondra being so much finer in texture. Perhaps more differences would have been discovered had I kneaded the doughs more religiously. Perhaps next time…
Most of the info on this page came from On Food and Cooking by Harold McGee. This is an absolutely amazing book that you should definitely get if you are interested in the why behind cooking.Tweet