The Anatomy of a Wheat Kernel
To understand what part of wheat is removed, it is essential to first know the structure of a whole grain. A wheat kernel, or wheat berry, has three primary components: the bran, the germ, and the endosperm.
The Bran
The bran is the multi-layered outer skin of the edible kernel and is a rich source of antioxidants, B vitamins, and dietary fiber. It makes up about 14.5% of the kernel's weight and provides a coarse, flaky texture.
The Germ
This is the embryo of the wheat plant, which contains concentrated nutrients, including B vitamins, minerals, protein, and healthy fats. The germ accounts for about 2.5% of the kernel's weight and is the part that could sprout into a new plant.
The Endosperm
The endosperm is the largest part of the kernel, making up around 83% of its weight. It is the germ's food supply and contains mostly starchy carbohydrates, proteins, and some vitamins and minerals. This is the component that is left behind after milling for refined flour.
The Industrial Milling Process
To produce refined white flour, wheat grains undergo a multi-step milling process. Modern roller mills are designed to efficiently separate the three main parts of the kernel. The primary steps are:
- Cleaning and Conditioning: The raw wheat is cleaned to remove foreign materials. It is then conditioned by adding a precise amount of moisture to toughen the outer bran and make the inner endosperm softer.
- Breaking: The conditioned grains are passed through a series of breaking rollers. These rollers crack open the kernels, separating the endosperm from the bran and germ.
- Sieving and Purification: After each pass through the rollers, the broken pieces are sifted through screens. Large bran particles are removed, and purification machines use air currents to separate lighter bran particles from the heavier endosperm fragments.
- Reduction: The remaining endosperm fragments, now called 'middlings,' are sent through a series of reduction rollers. These rollers grind the endosperm into a fine, white powder.
- Packaging: The finished, refined flour is then ready for packaging and distribution. If whole wheat flour is being made, the separated bran and germ are re-introduced to the ground endosperm.
Why Are Parts of Wheat Removed?
The removal of the bran and germ serves several commercial purposes, which have significant trade-offs:
- Extended Shelf Life: The most critical reason for removing the germ is its high content of fatty acids. These fats can oxidize over time, causing the flour to go rancid and shortening its shelf life. By removing the germ, refined white flour can be stored for much longer.
- Texture and Appearance: Consumers often prefer the fine, soft texture and white color of refined flour for baking cakes, pastries, and other delicate goods. Removing the fibrous bran and oily germ results in a more consistent and predictable product.
- Taste: The strong, nutty flavor of the bran and germ is also removed, creating a more neutral-tasting flour that many find more versatile for a wider range of culinary applications.
Nutritional Trade-offs: Whole vs. Refined
The table below compares the nutritional content of whole wheat flour (with all parts intact) and refined white flour (with bran and germ removed).
| Feature | Whole Wheat Flour | Refined White Flour |
|---|---|---|
| Composition | Contains bran, germ, and endosperm | Contains only the endosperm |
| Fiber | High in dietary fiber, particularly insoluble fiber from the bran | Significantly lower in fiber, as the bran is removed |
| Vitamins | Rich in naturally occurring B vitamins (B1, B3, B5) and vitamin E | Lower in natural vitamins, although often enriched after milling |
| Minerals | Higher levels of essential minerals like iron, zinc, and magnesium | Lower in natural minerals due to the removal of the bran and germ |
| Shelf Life | Shorter shelf life due to fats in the germ | Longer shelf life because the germ is removed |
| Texture | Denser, coarser texture, often producing heartier baked goods | Fine, softer texture, ideal for light and fluffy baked goods |
Enriched refined flour has some vitamins and minerals added back, such as B vitamins and iron. However, the fiber is not replaced, and it still lacks the full range of nutrients found in whole grains. As the USDA recommends making at least half of your daily grain intake whole grains, understanding these differences is crucial for a balanced diet. For more information on whole grains, visit the Whole Grains Council website.
Conclusion
In summary, the parts of wheat that are removed during the milling process are the bran and the germ, leaving only the endosperm. This refining creates a white, soft flour with a longer shelf life but strips it of significant nutritional content, including fiber, vitamins, and minerals. While enriched refined flour has some nutrients added back, it is not nutritionally equivalent to whole wheat flour. Therefore, choosing whole-grain options helps retain all the natural benefits of the complete wheat kernel.
