Watching "The Great British Baking Show" recently, I was intrigued by the judges' comments. They would glance at piece of bread and immediately say
"You proofed it for too long" (or not long enough)
"You kneaded it too much" (or not enough)
"Overbaked" (or underbaked)
"Oven was too hot" (or too cool)
"The wrong flour"
"Too much liquid"
They really seemed to know all about the process and what can go wrong. (It sounded complex and lots could go wrong).
That led me to wondering about the science behind baking bread. Humans have been baking bread for thousands of years. At its simplest, all you do is mix flour and water, and bake it. But it gets more complicated and there's a lot of science involved.
Want more dough? As for a raise.Flour and water and 18 minutes of baking will get the flat bread called matzah. Most people who eat this for a week find it boring, to say the least. Comparisons to cardboard are common.
|Jews are required to eat matzah and no leavened bread for the seven days of the Passover festival.|
It's not as quick and easy, but using yeast to get the carbon dioxide bubbles tastes better and is more versatile for getting different bread textures. Yeast is a single celled fungus that feeds on sugar and transforms it into alcohol and carbon dioxide gas.
|Yeast cells at a magnification of 400|
What else do we need?We need some sort of framework to capture the carbon dioxide bubbles. The best material for this is gluten. Gluten consists of long, elastic protein chains, which form rubbery networks, perfect for capturing gas. It's a lot like a balloon. Handily, wheat flour contains two proteins, glutenin and gliadin which, when combined with water, form gluten.
The more protein in the flour, the more gluten it has. That's why cake flour and bread flour are different. Bread needs much more gluten than cakes do. Bread flour has about twice as much protein as cake flour. This video
has a great demonstration of the difference and really shows the elastic property of gluten.
Most bread recipes mix the dry and wet ingredients and then leave the dough for an hour or two to do its magic: breaking down the starch to form sugar, which feeds the yeast cells, giving off bubbles of carbon dioxide which are captured in the gluten network. The dough will rise to about double its original volume. This is called proofing.
Then you knead the dough by repeatedly folding at and squashing it. This helps develop the gluten network to make it stronger and more elastic. Some recipes repeat the process of letting the dough rise and kneading it - sometimes several times.
Now we're cooking!It's time to bake. As the dough heats up in the oven, the carbon dioxide bubbles expand. New bubbles are also formed because the alcohol (remember that yeast produces both carbon dioxide and alcohol) and the water which the starch absorbed, both vaporize. So the dough rises again. This is called "oven spring".
|Illustration of heat transfer from Modernist Bread, The Cooking Lab|
If the experiment was successful, you now have a hot, crusty, delicious loaf of bread.
Full disclosure: I haven't yet put any of my newly discovered information to the test of actually baking bread. But I will!