Wheat Germ

The wheat kernel has three functional parts: the starchy endosperm that becomes flour, the bran layers that enclose it, and the germ. The germ is the embryo, set at one end of the kernel, and it is provisioned quite differently from the starch reserve beside it — where the endosperm is a store of starch and protein, the germ carries the oil, the enzymes, and the concentrated nutrients an emerging seedling would need. It is a small part of the grain holding a disproportionate share of what is nutritionally interesting in it.

Roller milling separates it by exploiting how differently it behaves. Correctly conditioned germ is tough and oily and flattens rather than shatters when it passes between rolls, while the endosperm around it breaks away as friable fragments. A flake of germ and a chip of endosperm are then different enough in size, shape, and density for sifting and purification to part them. The germ recovered this way is characteristically flaky, which is why it is sometimes sold and described as germ flakes.

Flour with germ in it does not keep as long as flour without. The germ’s oil is vulnerable to going rancid, and the kernel carries lipase — an enzyme that acts on that oil — right alongside it. In the intact grain the two are held apart and the arrangement is stable, which is why wheat can be stored for a long time. Milling breaks the kernel open and ends that separation, so the oil and the enzyme that degrades it are mixed together in the product. The result is a flour with a shorter usable life than a miller or a baker wants.

This also explains why germ is a co-product rather than a by-product. It is separated deliberately and by design, it is recovered as a distinct stream rather than blended away into mill feed, and it earns a price that forms part of what a mill makes from a tonne of wheat. A mill that simply wanted the germ gone could allow it into the lower-value blended streams; recovering it cleanly as germ is a choice made because the stream is worth something.

Germ goes to food and to feed. Its food use rests on the same concentration of oil and nutrients that made it a problem in flour: it is sold as a food ingredient in its own right and added back into breads, cereals, and other foods where its nutritional contribution is the point. It is also a raw material for wheat germ oil, which is extracted and used in food and in cosmetic applications. Where a food outlet is not available or not economic, germ is a feed ingredient, and the meal remaining after oil extraction is fed as well.

• Food — sold as an ingredient and added to breads, breakfast cereals, and other foods
• Oil — extracted as wheat germ oil for food and cosmetic use
• Feed — whole germ, and the meal left after oil is extracted

Germ intended for food is usually stabilised — most commonly by heat treatment that deactivates the lipase — because untreated germ has the keeping problem that got it separated from the flour in the first place, only more so, concentrated. Stabilisation is what turns a stream that must be moved on quickly into an ingredient that can sit on a shelf.

Germ is bought on how cleanly it was separated and on the condition of its oil. Adhering endosperm and bran dilute the stream and lower its value, so purity is a commercial attribute rather than a cosmetic one. Free fatty acid content is the other central measure, and it is a moving target rather than a fixed property: once the kernel is opened, lipase and oil are in contact, and germ held warm and damp degrades. The interval between the mill and stabilisation or extraction is therefore itself a quality variable.

The handling follows from that. Unstabilised germ is not a stream to hold — it is kept cool and dry and moved on promptly rather than stored, while stabilised germ keeps far better and is packed and traded as a food ingredient. Germ is light and flaky and free-flowing, so bulk handling is straightforward, but its oil makes residues in conveying equipment a housekeeping matter. As with any fraction concentrated out of the kernel, whatever the incoming grain carried follows the stream, so the soundness and cleanliness of the wheat and the mill’s cleaning bear directly on the germ.