The chemistry of dough

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People have been baking bread for thousands of years, so you’d think that they already figured out how to do it best. After all, what you need to do is basically mix some flour and stuff, scorch it and voila: Bread. So I was rather surprised to learn that there is a lot of interesting chemistry going on in dough. Actually there is a whole industry involved in researching enzymes and other additives that help the chemistry of baking bread along.

Some of the most interesting bred chemistry starts right after mixing the ingredients. One of the really important jobs, apparently, is to keep the dough oxidized. If you pour water over your flour, the first thing that will happen is that some starch and water combine into the well-known starch glue. As a result the proto-dough is a sticky mess. After a while, however, change happens and the dough becomes smooth and elastic. Behind this change are two proteins, gliadin and glutenin. The latter is a chain-like protein containing cysteine, which can form disulphide bonds to cysteine in gliadine and other proteins.

During kneading of the dough, disulphide bonds are formed, broken and re-formed, until the Proteins form a huge Network throughout the dough. It’s actually a bit like vulcanizing rubber. Unfortunately there is a lot of glutathione around, too. Glutathione is part of the cellular redox buffer and it competes with the formation of the protein network.

There are several things you can do to prevent this. Adding an oxidant like ascorbic acid works pretty well but that’s the drawback, too: There are a lot of additional disulphide bonds formed almost instantly, so the dough thends to crumble during kneading. Oxidizing Enzymes on the other hand work a bit slower, so the network fully develops ony when the loaves are already formed. That’s why people use glucose oxidase nowadays. But there are already other, specialized oxidoreductases in the pipeline.

But the most important chemistry starts when the bread enters the oven. I’m sure I don’t need to introduce you to the maillard reaction which creates the brown crust and all those nice flavors. But there’s a more subtle change going on within the loaf, too. The Proteins lose their plasticity, and the network between them becomes permanent. Also the starch grains pop open and the long-chain carbohydrates become exposed to Enzymes that degrade them into smaller oligosaccharides, the dextrines. All components are now baked into the firm, yet foamy structure of bread. So if you happen to bake your own bread, spare a thought for the complex chemistry that makes our daily bread.

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