© 2008 Shutterstock.
© 2008 Shutterstock.

Recently, in a fit of back-to-basics vigor, I tried to recreate the process of grinding wheat into flour using two rocks and succeeded only in distributing the squashed grains unevenly on the ground and getting very sweaty and annoyed. Making a fire the old fashioned way, by contrast, is both much easier and rather impressive. It is virtually impossible to not stand back from the nascent flickering flames and swagger about, feeling, well, er…yes, manly, and look around for something tasty to roast. What then, made the back-breaking bread process so irresistible to our ancestors?

The standard answer to this question is to be found in many anthropology books, including the classic Guns, Germs and Steel by Jared Diamond, and comes down to the large number of calories per acre that wheat can reliably yield. If you want to live sociably in large communities, villages, and ultimately cities, it turns out you need to cultivate cereals. Thus, the process of making bread is central to many cultures and languages, the word lord for instance has the Anglo Saxon route of ‘loaf giver’ and lady of ‘loaf kneader’; the word company comes from the Latin campinaro, meaning ‘sharing of bread’.

Bread is also an important part of the history of materials science. It's not just that our specimen preparation technology has an unbroken line of descent from the first wheat grinding stones, windmills, and milling machines. Or that the development of furnace technology is intimately associated with the development of cooking ovens. But there is also a link to our love of foams and sponges and how to make them.

The first thing you notice when mixing flour and water is that you make a rather pleasing visco-plastic dough. It is a material which appears alive and springy, outside one's normal experience, with characteristics that seem to transfer quickly from the dough to your hands. It is virtually impossible not to feel rather playful and perky when kneading dough, it feels special, and it is. Wheat is an almost unique grain. It contains a very high proportion of gluten proteins that give the dough very special structural properties, allowing tiny bubbles of carbon dioxide to grow through the action of yeast, into a visco-plastic foam. It is very hard to produce a fine foam with the flours of other cereals, as anyone who has tried to make gluten-free bread will attest. In between the membranes of the wheat foam are the starch granules which give the final bread its sweetness, stature, and also through other Maillard reactions, the caramel and nutty flavors, so intoxicating to those within sniffing distance of a bread oven.

Having developed the key to the microstructure of dough, it is the heat treatment that creates the bread. Upon entering the oven, the dough warms and as it does so, the trapped carbon dioxide expands and pushes on the gluten membranes causing the whole mass to puff up. As the temperature increases, the proteins cross-link, meanwhile the carbohydrate starch granules absorb water, swell, and gelate. Simultaneously, the exterior dries out and forms a continuous crust creating a back pressure on the rising foam. The foam membranes lose their visco-plastic properties and under internal pressure burst open, connecting with each other and forming a sponge structure. This is vital, otherwise upon cooling the individual carbon dioxide bubbles would shrink, causing the bread to collapse. Thus, controlling the rate of foam expansion, the rate of reactions, and the formation of the crust, are the technical skills needed to make this most wonderful and spiritually comforting edible sponge.

There's a lot of snobbery surrounding the making of bread. Performed in a kitchen, where each loaf is hand-made, it is lauded as the expression of the ultimate homely art. Performed in a factory, it is often castigated as an unwelcome scientific intrusion into the natural order of food preparation. But it is worth noting that factory-made bread has been a triumph for social equality: currently an average American is required to work only four minutes in order to afford a loaf of bread, contributing greatly to the reduction of real poverty. But has taste been sacrificed? Probably, but ultimately this is a subjective judgment which depends on your hunger. I am sure our ancestors would not have minded having to work only four minutes a day in order to eat a loaf of bread, they had a lot of other things to do. A modern person with less to do may feel differently.

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DOI: 10.1016/S1369-7021(08)70162-7