Understanding the Whole Kernel: What is the composition of wheat grain?

January 13, 2026 •

2 min read

Wheat is a major staple food providing about 20% of food energy and protein worldwide. Understanding what is the composition of wheat grain is key to appreciating its nutritional value and the differences between whole and refined wheat products.

Quick Summary

The wheat grain is composed of three edible parts: the bran, the endosperm, and the germ. Each part has a unique nutrient profile that influences its culinary use and health benefits.

Key Points

Three Main Parts: A wheat grain consists of three distinct edible components: the bran, the endosperm, and the germ.
The Bran's Role: The outer bran layer is a major source of fiber, B vitamins, minerals like iron and zinc, and health-promoting antioxidants.
Endosperm Dominance: The endosperm is the largest part of the kernel, rich in starchy carbohydrates and protein, and is the source of white flour.
The Germ's Nutrient Density: The germ is the embryo and the most nutrient-packed part, containing healthy fats, Vitamin E, protein, and more B vitamins.
Milling's Impact: The milling process for refined grains removes the bran and germ, significantly reducing the fiber, vitamins, and minerals in the resulting flour.
Whole vs. Refined: Whole grain products contain all three parts of the kernel, offering more comprehensive nutritional benefits compared to refined and enriched products.

The Fundamental Structure of a Wheat Grain

The structure of a wheat grain, also known as the wheat kernel, consists of three primary, edible components: the bran, the endosperm, and the germ. These parts are separated during milling to produce different flour types. Understanding each part's nutritional makeup is crucial for grasping the distinction between whole grains and refined grains.

The Bran: The Protective Outer Shell

The bran is the hard, multi-layered outer skin, making up about 14.5% of the grain's weight. It's rich in dietary fiber, aiding digestion. The bran also contains:

Antioxidants like lignans and phenolic acids.
B vitamins (thiamin, riboflavin, niacin).
Minerals (magnesium, iron, zinc, phosphorus, copper).
Some protein.

The Endosperm: The Starchy Core

The endosperm is the largest part, about 83% of the kernel's weight. It's the source of white flour after the bran and germ are removed during milling. The endosperm mainly consists of:

Starch for energy.
Proteins, including gluten-forming types.
Minor amounts of B vitamins and trace minerals.
Lower fiber than the bran.

The Germ: The Nutrient-Rich Embryo

The germ is the kernel's embryo, comprising only about 2.5% of its weight. It's the most nutrient-dense part. The germ contains:

Healthy fats and oils.
Vitamin E and other antioxidants.
B vitamins (folate, thiamin, riboflavin).
Protein with a good amino acid profile.
Trace minerals (magnesium, iron, zinc, phosphorus).

Comparison of Wheat Grain Components


Component	Weight Contribution	Primary Nutrients	Milling Outcome
Bran	~14.5%	Fiber, B vitamins, minerals (iron, magnesium, zinc), antioxidants	Removed for white flour production; included in whole wheat flour.
Endosperm	~83%	Starch (carbohydrates), protein (gluten), minor vitamins and minerals	Milled into white flour.
Germ	~2.5%	Healthy fats, vitamin E, protein, B vitamins, trace minerals	Removed for white flour; included in whole wheat flour; can be sold separately.

The Impact of Milling: Whole vs. Refined Grains

Milling separates the grain's components, determining if flour is "whole" or "refined". Whole wheat flour includes all three parts. Refined flour uses only the endosperm, removing the bran and germ and thus reducing fiber, B vitamins, minerals, and antioxidants.

While some refined flours are 'enriched' with synthetic nutrients, they lack the full nutritional profile of whole grains, such as fiber, healthy fats, and phytochemicals. The oils in the germ give whole wheat flour a shorter shelf life. Whole grains are linked to health benefits due to their higher fiber and antioxidant content.

Conclusion

To summarize, the composition of wheat grain includes the bran, endosperm, and germ, each contributing unique nutrients. Milling separates these parts, affecting the nutritional value of the final product. Whole wheat products, containing all three components, offer more comprehensive health benefits than refined grains, which lack the bran and germ. Understanding this structure helps consumers make informed dietary choices. More information can be found on resources like Feedipedia.

Frequently Asked Questions

The three main edible parts of a wheat grain are the bran, the endosperm, and the germ. The bran is the outer layer, the endosperm is the starchy core, and the germ is the embryo.

White flour is made exclusively from the endosperm. The bran and germ are removed during the milling process, which is why white flour contains less fiber and other nutrients than whole wheat flour.

Wheat bran is particularly rich in dietary fiber, B vitamins, antioxidants, and minerals such as magnesium, iron, zinc, and phosphorus.

Yes, the germ is the most nutrient-dense part of the wheat kernel by weight, containing high concentrations of healthy fats, Vitamin E, protein, and B vitamins.

Whole grain is generally considered healthier because it contains all three parts of the grain and their associated nutrients, including fiber, healthy fats, vitamins, and antioxidants. Refined grain lacks the bran and germ.

Yes, whole wheat flour typically has a shorter shelf life than white flour. This is because the germ, which contains natural oils, is included in whole wheat flour but removed during the production of white flour. These oils can turn rancid over time.

The endosperm contains gluten-forming proteins like gliadin and glutenin. When mixed with water, these proteins create the unique elastic and sticky properties of dough that are essential for making leavened bread.