Wheatstalk Part 3: How Wheat Becomes Flour

Andrew’s 4-part adventure will be posted over the course of this week. Read all of his Wheatstalk coverage here.

The first half of day 3 of my Wheatstalk adventure involved a slideshow presentation entitled “From Wheat to Flour,” given by Tim Huff and Bruce Hoshor, both from General Mills, one of the largest flour producers in the United States. As the title suggests, the talk followed the life of a grain of wheat from field to bag of flour on a supermarket shelf.

Compared to doughnuts and beignets, this was dry stuff, but still, for a breadhead like myself, it was still pretty interesting. In the end, I discovered that even someone like me—someone who works with a wide variety of flours on a regular basis—had lots to learn about the subject. Except when I’m grinding my own flour from wheatberries, I never give much thought to how the flour I use ends up in the form it is. As it turns out, the process is far more complicated than I could ever have imagined.

Milling performs two functions: The first is to isolate the starch-containing endosperm in the grain from the bran (the tough, outer husk of the wheat kernel) and the germ (the oil-rich embryonic wheat plant). The second is to reduce the endosperm to flour.

But before milling can even begin, a few things must happen. First, the grain must be cleaned. Straight from the field, a truckful of wheat can contain numerous contaminants: weed seeds, dirt, fungi, stones, and even shards of metal.

These are removed from the grain in a variety of ways: by passing the grain through or over screens of different mesh sizes; under magnets, to remove metal-containing objects; above blown air, to remove lighter weight components, and over indented rollers, to separate out weed-seeds of different shapes.

Once the grain is clean, it undergoes a “tempering” process, to bring it to an optimal moisture level. It is sprayed with water and then allowed to sit in temperature-controlled bins until it reaches the desired hydration.

This is a schematic of a single milling process, showing each of the individual milling, sifting, and purification stages through which a load of wheat travels as it is transformed into flours.

Milling itself involves three distinct processes: grinding, which breaks the grain into its component parts and reduces them in size; sifting, which separates out different components by size; and purification, which removes unwanted components from the flour that cannot be separated by size.

Grinding is accomplished by passing the grain through metal rollers that look not unlike giant pasta rolling machines. In the first stages, so-called “break” rollers crack open the kernel and separate the endosperm from the bran layers.

Break rollers are often corrugated to produce various results; additionally, the paired rollers move in the same or in opposite directions, and at different rates, relative to their partners.

Once the grain has been broken, it is sifted to separate components by size and then sent to “reduction” rollers, which reduce the endosperm to the desired fineness to produce something that starts to look like flour. Rather than transforming the particles by grinding action, reduction rollers utilize the pressure produced by the rollers to reduce the size of the flour particles.

Sifting occurs both during and after the milling process. The flour is passed through a series of stacked, vibrating wire or nylon mesh screens and separated into various “streams” by particle size. Sifting serves three functions: to remove larger bran and germ particles, to “grade” larger endosperm particles so that they can be returned to the rollers for further processing, and to collect particles less than 130 microns in diameter as flour. As the individual streams emerge from the sifters, they are moved around the mill through pipes using forced air.

The final stage of milling is purification, where the flour is cleaned of bran particles that have survived the sieving process. Purification is accomplished by pushing air currents through the flour as it passes over screens; less-dense bran particles float upwards, where they can be easily removed.

Milling produces a variety of different grade “flours,” but none are flour as we think of it quite yet. This is because the flour found in bags at the grocery store is actually a blend of various milled products, most of which likely came from different sources. Milling is the process of dividing the grain into various components; only through blending do they come together to make flour. This is true even for so-called “whole” grain flours such as whole wheat; they are whole in the sense that each contains most of what can be found in the grain, but they are blended like all other flours. Blending allows flour manufacturers to create a product with specific characteristics from a variety of grain sources.

It is in the blending stage that manufacturers also incorporate malt, to increase the enzyme activity of the flour (which insures proper rise), and vitamins and minerals, as is required by FDA regulations.

Perhaps the most surprising thing I learned was just how much variability there can be in flour from bag to bag. While we tend to think of one brand or style of flour as a consistent and reliable thing, it’s not really true in practice. Though manufacturers expend a lot of effort to produce a flour with very specific characteristics, it’s impossible to have any particular flour behave perfectly identically from batch to batch.

The greatest source of variability in flour comes from environmental factors influencing the quality of the wheat—rainfall patterns, temperature, soil conditions, nutrition, etc. And apparently, there is only so much that can be done in the mill to adjust for deficiencies from one year’s crop to the next, so flours can and do change quite frequently.

Obviously, this variability of great concern to commercial bakers, who strive for consistent results day in day out, and who often need to make adjustments to their formulas for each new batch of flour they receive.

But it’s actually no different for the home baker. You might think the bag of flour you pull from the shelf today will behave identically to the one you purchased last time around, or last year, but it very well might not. Your recipe could need more water, or longer kneading times, to achieve results similar to last time around. Keep this in mind next time you find a recipe has gone awry, even though you’re sure you’ve followed instructions to the letter.

The remainder of the 3-hour class covered such topics as how to read a farinograph, how to determine the “ash content” of the flour, and what the hell a “Chopin alveograph” is, all of which is only of interest to the most obsessive bread nerd (or the professional baker). I learned a lot in the short class, and will certainly never look at a bag of flour the same way again.

Will you?

(Slides courtesy of Tim Huff and Bruce Hoshor)