In their raw form, grains of wheat do not look particularly appetizing – they're small, dense, and covered in a tough woody coat six layers thick. This is actually the fruit of the wheat plant, and, as difficult as this may be to believe, that tough little kernel has a distant kinship with much more edible fruit.
Fruits are characterized by an outer layer of tissue called the pericarp. In most cases, the pericarp is fleshy, like in apples, oranges, or bananas (to name a few examples). Nuts, in contrast, have a dry, woody pericarp. Wheat, as with all members of the grass family, share this woody pericarp, but it is reduced in size and fused to the seed itself, leading to a separate classification as a “caryopsis” (“berry,” being more recognizable and easier to pronounce, has most certainly been the more popular, if botanically incorrect, nomenclature).
This structure is indicative of the grasses' evolutionary strategy. When dealing with animals, many fruit-bearing plants have decided that if they couldn't beat us, they might as well join us and offer us a tasty reward for spreading their seeds in the form of fruit. Under ideal circumstances, the animals eat the fruit, swallow the seeds whole, and pass them undamaged through the digestive tract to leave them behind in a nice little dollop of fertilizer some distance away from the parent plant.
Grasses, on the other hand, tend to put less stock in long-distance dispersal and more in guaranteeing the success of their offspring by providing a richer store of nutrients. If your strategy as a seed relies on being swallowed, then your potential size is constrained by the diameter of your animal disperser's gullet. This is a particular problem for seeds from fruit dispersed by small animals, such as strawberries or blackberries. Grasses instead produce larger seeds with more nutrients that don't scatter as far from the parent plant. Since they've decided to skimp on bribing animals, they have to sheathe their seeds in tough woody layers to avoid being eaten. Animals, being crafty, have found a workaround: grind the grains up with stones, a strategy employed both by humans and birds.
In a wheat grain, both the pericarp and the seed coat (or testa) are collectively known as the bran. The bran, being quite closely related to wood, is rich in fiber. A third layer, known as the aleurone layer, separates from the interior of the grain with the bran. Aleurone is a storage protein (like glutenin and gliadin) that holds onto fats as well as some vitamins and minerals, making bran a good source of magnesium, manganese, and selenium. Finally, the bran is home to a compound known as phytic acid, a complex molecule built to store phosphorus until it's needed for DNA synthesis when the seed germinates.
The next layer in the wheat grain is the endosperm, which forms the majority of the grain's weight and caloric content. This layer consists mainly of starch and the storage proteins gluten and gliadin, which serve to fuel the growth of the young seedling. White flour is primarily made up by of endosperm.
The final layer of the grain is the most important: the germ. The germ is an embryonic plant, packed up and dormant until the seed imbibes water and the hull begins to split. The germ holds a lot of important enzymes for taking apart the rest of the wheat grain – proteases for digesting storage proteins, amylases for turning starches into sugars, and phosphatases for breaking up phytic acid.
When the grain is ground, all of these compounds end up in the final product to a greater or lesser degree. Yet, were you to go eat a spoonful of raw flour, it would taste a lot like eating sawdust. To really become palatable, flour requires a lot more processing. In my next post, I'll explain how we can turn a pile of starch, protein, and enzymes into something worthy of the dinner table. Until then, stay hungry!