Oat and wheat bran are chemically quite different. Oat bran has no gluten. Wheat bran has significant gluten. Now bran of any kind has less gluten than endosperm, which is largely the composition of most flour, so large amounts of bran are going to interfere with the rise. But wheat bran ought to allow for better rise than oat bran. Can anyone confirm this? I add wheat bran to regular bread flour for my sandwich loaves, giving me somewhat more bran than whole-wheat.
It's not the absence of “gluten” in the bran that causes a low rise. Rather, the sharp edges of the bran cut and destroys the gluten network during kneading.
Just a point of clarification, there is NO gluten in wheat flour.
Wheat flour contains two protein molecules: glutenin and gliadin.
Glutenin and gliadin must bind with a water molecule AND be agitated to form a gluten network.
- Glutenin is the larger of the two protein molecules; it gives dough strength and elasticity (ability to hold its shape)
- Gliadin is very sticky and gives dough extensibility (ability to stretch)
Dough elasticity and the strength of the gluten network depends on the amount of glutenin, and the ratio of glutenin to gliadin.
Since the amount of glutenin and gliadin varies by wheat variety, millers separate the kernel into its parts, mill them separately into flours, then blend different ratios of the flours to create a flour (more on milling below).
The wheat kernel consists of three major parts:
Bran: 14.5% of the kernel weight; the outer shell of the kernel
Endosperm: 83% of the kernel weight; the starchy center that the white flour is milled from
Germ: 2.5% of the kernel weight; the embryo of the kernel.
In most milling (not French), the wheat kernel is separated, then each part of the kernel is milled. The separately milled parts are called streams.
The endosperm is milled in two parts; the center is milled separately from the part that is closest to the bran. The reason is there is some bran residue on the endosperm.
Patent flour is the flour milled from the center of the endosperm. It is pretty much pure starch and has a lower ash content since there is no bran residue. It has less taste, is finer in texture, and is lighter in color. This is the starchiest part of the kernel.
Clear flour is milled from the outer part of the endosperm. It is still pretty much pure starch, but the ash will be slightly higher since it has some bran residue. It has more taste, is coarser in texture, and darker in color than patent flour.
Endosperm is where the amino acids, glutenin, and gliadin are stored. When glutenin and gliadin bind with water molecules AND are agitated, they form a gluten network.
After the bran, endosperm, and germ are separated and milled, they are blended to create different flours. The amount of each flour in the blend determines the type of flour.
Blending all the bran, endosperm, and germ makes whole wheat (wholemeal) flour. Normally clear flour is used to make whole wheat since it is darker in color, coarser in texture, and more distinct in taste.
Blending approximately 73% of the bran and germ into patent flour makes all-purpose flour.
Blending approximately 45% of the bran and germ into the patent flour makes pastry flour.
Only the two endosperm flours have the amino acids (proteins) that contribute to gluten: glutenin and gliadin.
All flours are made by blending the flour streams in different proportions. These different proportions are called extraction rates. 100% extraction means 100% of the kernel is used to make the flour.
whole wheat is 100% extraction
cake flour is 45% extraction
Once blended this results in various levels of glutenin and gliadin (protein) and ash in the flour.
It’s not uncommon for different varieties of wheat to be used in flour. Just because it says hard red wheat on the bag, doesn’t mean there’s just one variety of wheat in the sack. Remember, glutenin and gliadin content varies by wheat variety; so a miller will blend using different varieties to create certain performance characteristics.
Wheat varieties suitable for cake and pastry are not suitable for bread. And vice versa.
The protein and ash levels are related. The higher the protein content, the higher the ash.
French milled flour:
Not all flour is milled by separating the wheat kernel into its parts.
The French mill the entire kernel, then sift out the amount of bran and germ to create the flour they want. Since the entire wheat kernel is milled, some of the bran and germ are embedded into the endosperm flour. So the mineral content (ash) is higher than its counterpart.
A French milled flour has more flavor, is nutrient richer, and has more color than its counterpart. French flour performs better in that it performs like a higher protein flour than flour that has been milled by separating the wheat kernel.
French flour is labeled by ash content.
T45 equivalent to pastry flour
T55 equivalent to all-purpose flour
T65 equivalent to bread flour
T85 there’s no equivalent in American flours. It’s a higher extraction flour, not whole wheat. So you get some of the benefits of whole wheat but some of the nicer attributes of an all-purpose.
French flours produce better volume and texture because of the cultivars and the milling. It is also the reason why when it comes to bread and laminated dough, the top bakers in the world prefer French flours.
To increase flavor, color, and nutrients in baked goods, it is better to blend your regular flour with a flour like T85 rather than adding bran. The reason is the miller selects wheat varieties and blends the ideal potions of various flours to create optimal performance, flavor, and nutrition.