CEREAL TECHNOLOGY: WHEAT MILLING
Diagram
Flour from the whole grain, and flour from the endosperm only
Whole wheat flour
Flour milled from the whole wheat kernel: bran, germ and endosperm together. Brown, coarse, rich in fiber.
↓
Refined flour
Flour milled from the endosperm only, after the bran and germ are removed. White, fine, mostly starch and protein.
Figure 1: Whole wheat flour keeps bran and germ, while refined flour is only the endosperm. Drawn in our own style from the milling discussion in Cornell and Hoveling, Wheat: Chemistry and Utilization, Chapter 2, The Milling of Wheat.
Introduction
Whole wheat flour and refined flour both come from wheat, but they are milled from different parts of the kernel. A wheat kernel has three parts: the bran, the outer coat rich in fiber; the germ, the small embryo rich in oil, vitamins and minerals; and the endosperm, the starchy middle that holds most of the protein. Whole wheat flour is milled from all three parts together, so it keeps the fiber, the vitamins and the minerals. Refined flour is milled from the endosperm only, after the bran and germ are sieved away, so it is white and fine and mostly starch and protein.
Quick comparison
Table 1: Whole Wheat Flour compared with Refined Flour
| Aspect | Whole Wheat Flour | Refined Flour |
|---|---|---|
| Parts of the kernel used | Bran, germ and endosperm | Endosperm only |
| Colour | Brown | White |
| Texture | Coarse, with visible bran | Fine and smooth |
| Fiber | High, from the bran | Low, because the bran is removed |
| Vitamins and minerals | Kept, from the bran and germ | Mostly lost, unless the flour is enriched |
| Fat | Higher, from the germ oil | Low, because the germ is removed |
| Keeping quality | Shorter, because the germ oil turns rancid | Longer, because the oil-rich germ is gone |
| Water absorption | Higher, because fiber absorbs water | Lower |
| Bread made from it | Denser, darker, with a nutty flavour | Lighter, whiter, with a larger volume |
| Gluten | Present, but the bran cuts the gluten strands | Present, and it forms a stronger network without bran |
Scientific explanation
Definition
Whole wheat flour is flour milled from the whole wheat kernel, bran, germ and endosperm together. Refined flour is flour milled from the endosperm only, after the bran and germ have been removed by milling and sieving.
Working principle
Milling starts by cleaning the wheat and breaking the kernel in roller mills, then sieving the pieces. The endosperm breaks into fine white flour, while the bran comes off as coarse flakes and the germ as small oily pieces. For refined flour, the bran and germ are sieved away and only the endosperm flour is kept. For whole wheat flour, the bran and germ are milled fine and put back, so the flour holds all three parts. The bran fiber absorbs water and cuts through the gluten network, so whole wheat dough is heavier and the bread is denser, while refined flour gives a strong gluten network and a lighter loaf.
Apparatus
The books used here name no laboratory apparatus for measuring or comparing either term, so no apparatus list is given.
Measurement procedure
The books used here give no standard laboratory procedure with volumes and steps for either term, so no procedure is invented here.
Factors affecting readings
For both flours, the wheat variety and the milling decide the protein and the fineness: hard wheat gives more protein than soft wheat. For whole wheat flour, the fineness of the bran decides the texture: coarse bran cuts the gluten more than fine bran. Storage matters for whole wheat flour, because the germ oil oxidises and turns rancid, so it keeps for a shorter time than refined flour.
Formulas and calculations
The books used here give no formula for either term, so no formula is given here.
Industrial applications
- Whole wheat flour: whole wheat bread, chapatis and other whole grain foods, where fiber and flavour matter.
- Whole wheat flour: breakfast cereals and biscuits made from the whole grain.
- Refined flour: white bread, cakes and pastries, where a light colour and a large volume are wanted.
- Refined flour: noodles, biscuits and general baking, where a fine, smooth flour is wanted.
- Both: blended flours, where whole wheat and refined flour are mixed to balance flavour and volume.
Advantages and limitations
- Whole wheat flour, advantage: it keeps the fiber, vitamins and minerals of the bran and germ.
- Whole wheat flour, limitation: it keeps for a shorter time, because the germ oil turns rancid, and its bread is denser.
- Refined flour, advantage: it keeps longer, gives a light loaf with a large volume, and suits cakes and pastries.
- Refined flour, limitation: it has lost most of the fiber, vitamins and minerals of the whole grain.
FAQ
What is the difference between whole wheat flour and refined flour?
Whole wheat flour is milled from the whole kernel, bran, germ and endosperm, while refined flour is milled from the endosperm only.
Why is whole wheat flour brown?
Because it holds the bran, the brown outer coat of the kernel.
Why does whole wheat bread feel denser?
The bran fiber absorbs water and cuts the gluten strands, so the loaf cannot rise as high.
Does refined flour have any vitamins?
Most are lost with the bran and germ. Some refined flour is enriched, with B vitamins and iron added back.
Which one keeps longer?
Refined flour keeps longer, because the oil-rich germ that turns rancid has been removed.
References and further reading
- FTN books on disk: Cereal Technology.
- Cornell, Hugh and Albert W. Hoveling. Wheat: Chemistry and Utilization. CRC Press, 1998 (Google Books page read)
- Greene, Diana Scesny. Whole Grain Baking.
- Google Books pages read for this article:
- Cornell, Hugh and Albert W. Hoveling. Wheat: Chemistry and Utilization. CRC Press, 1998 (Google Books page read)
