How Bread Works
By Jennifer Nemec | Dec 15, 2020
The process of baking bread often seems cloaked in mystery. You put a few simple ingredients together, follow a peculiar set of steps, and voilà, the staff of life. The process seems so alive, so magical, so … intimidating. My usual response to such fearful thoughts is to research how and why something works. Like most things that seem scary, bread is, at its heart, quite simple. The answer to the mystery of bread revolves around yeast and a protein called gluten.
Harold McGee, who literally wrote the book on science in the kitchen (On Food and Cooking), breaks the making of yeast bread down into four steps: “We mix together the flour, water, yeast and salt; we knead the mixture to develop the gluten network; we give the yeast time to produce carbon dioxide and fill the dough with gas cells; and we bake the dough to set its structure and generate flavor.” Sounds easy enough, right? OK, maybe it doesn’t just yet. Let’s break each step down individually.
Choosing and mixing your building blocks
Through the millennia humans have been making bread, its ingredients have become pretty specialized. Depending on your desired outcome (are you looking for an airy white bread or a dense, crusty artisan loaf?), you can take advantage of this quality.
The best strain of yeast has already been chosen for you (more on yeast later), you can filter your water (or buy bottled) to avoid any problems that minerals or the lack thereof might cause, and the most pristine salt is available right on your grocer’s shelf.
Flour comes in many types. Bread flour is made primarily from hard red spring wheat and has a higher amount of protein than all-purpose flour. These flours are “refined,” which means that portions of the wheat kernel (bran and germ) have been filtered out. If you’re looking for a more healthful loaf, you can add some whole-wheat flour, which includes the filtered bits, into the mix. You can’t just substitute whole-wheat flour for bread flour willy-nilly because, while wheat flour has more protein, the bran and germ don’t have the kind of protein needed to form the best gluten matrix and can actually cause a weakening of the structure. Other flours, like rice or corn, are also missing the crucial mixture of gluten proteins.
The mixing step is actually pretty important. Seems there’s a trick to the order that things go in the bowl, as anyone who’s ever tried to mix a whole lot of dry ingredients with a small amount of liquid knows. The yeast needs to be evenly distributed (to the point that some sift instant yeast together with the flour before adding liquid). The minute the water hits the flour, things start to happen. Even exposure to oxygen can make a difference.
The need to knead
At this point in the bread-making process, the dough gets agitated (in most cases). This takes some physical work and time. The dough is stretched and folded until it stiffens and takes on a satiny, elastic appearance. Kneading also creates tiny air bubbles that are later made larger by the work of the yeast. You might think of this like chewing gum. You have to chew it for awhile before it’s ready for blowing bubbles.
All this kneading is really about developing the gluten network. Gluten is made up of proteins in flour, glutenins and gliadins. Alton Brown, the king of cooking analogy, compares the structure of proteins to old-fashioned coiled phone cords. At the beginning of the bread creation process, picture a phone cord that’s been well-used. It’s twisted back on itself, and you’re having trouble getting it to stretch at all. In a glutenin molecule, weak bonds have even formed between different areas of the coils to keep it in a folded mass. One way to untangle these phone cords is to add water; this starts the process and allows the cords to unfold.
Imagine that the ends of these no-longer-tangled phone cords can attach to one another to form long chains. The stretching and folding of kneading allows these now-linear phone cords to align and join together. Once they are side by side, parts of the coils can then connect with each other. You now have created a kind of mesh structure made with chains of coiled proteins in the dough – the gluten.
Now think about how bread dough acts. When you stretch it out, it pulls against you and tries to creep back to its original position. That’s you stretching out the long rows of phone cords, and them pulling themselves back into shape.
The next stage, which most people call “rising” and the food scientists among us call “fermentation,” is a waiting period while yeast does its job. Yeast is a fungus, and the species used in bread baking is Saccharomyces cerevisiae (which means “beer sugar fungus”). The same action brewers use to create alcohol is the one bakers use for bread.
At one point in bread’s history, the local baker would take a sample of the froth remaining after brewing ale to leaven his bread. You could also use a portion of a previous loaf in the next, or, in cases such as sourdough, grow a “starter” of wild yeast in a crock of flour and water (see “Savory Sourdough” on Page 32 and the image below). Nowadays, you can just go to the store and buy yeast. Active yeast requires some wake-up time soaking in warm (105-110°F) but not hot (140°F will kill it) water, while instant yeast can be added to the mixture directly.
Yeast’s primary job in the bread-making world is to break down simple sugars into carbon dioxide and alcohol. Strangely enough, many of the sugars in flour aren’t easily available to yeast (which is why it takes longer to ferment bread dough than, say, grape juice). Most modern flours include an enzyme (amylase) that helps break down the wheat starch into simple enough sugars for yeast to handle. The carbon dioxide created inflates the air pockets and raises the dough. The alcohol becomes trapped in the dough as well, but don’t worry, it’ll cook off in the baking phase.
If your recipe calls for a high-protein flour, it may also call for more than one rise. Between rises, you “punch down” the dough. The point of this is to evenly distribute the gas bubbles and yeast for the second rise.
After the dough is finished fermenting, the baker carefully forms it into its final shape (whether that be loaves, rolls or complicated braids). It’s then prepared for baking and allowed to “proof” – which is a final partial rise and settling of the dough.
All this adding of air bubbles also assists in the lining up and stretching out of the gluten strands. And some of the byproducts of yeast’s action even help the phone cords line up end to end. You’ve fermented enough when your risen dough doesn’t “bounce back” when poked. At that point the gluten has been stretched to its limit.
Bring the heat
The dough goes through many changes in the cooking and cooling stages. When you put your bubble-filled gluten mesh into the oven, the first thing that happens is called “oven spring,” which, if you happen to be watching through the oven window, is kind of spectacular. The dough becomes more fluid, alcohol and water in the dough vaporize into the existing cells, and the loaf rises quickly.
The heat also firms the crust and begins to solidify the gluten and starch in the cell walls. The expansion inside continues, but, with nowhere to go, it eventually ruptures the walls between the cells. The structure of the dough changes from a foam of individual gas balloons to a sponge of interconnected holes. Without this transformation, when the bread cools, the gas cells would shrink again, and the bread would fall.
As cooking continues, the starches continue to set, and the surface browns. Your bread is ready when you tap on the outside and it sounds hollow rather than dense. Don’t cut into it immediately, though. Bread needs cooling time. The moisture inside equalizes, and the starch becomes firmer and easier to slice, although I’m not sure anyone can resist bread fresh from the oven.
Needs for no-knead?
How does all this phone cord aligning work with no-knead breads? Well, it’s about rising time and wet dough. I’ll lead with the words of my main man McGee, “The long, slow rise does over hours what intensive kneading does in minutes: it brings the gluten molecules into side-by-side alignment to maximize their opportunity to bind to each other and produce a strong, elastic network.”
He also says it’s important for the dough to be wet to allow gluten to form and move about. Because the rise is longer, you can use a smaller amount of yeast, which is a plus since it also means fewer yeast byproducts for this type of bread (see “Easy, No-Knead Artisan Bread” on Page 12). These are not your mother’s loaves with small, even cells – the air bubbles are less controlled with this method and therefore more varied.
What if I’m gluten-free?
Gluten is not the only elastic substance in the food world. Rye bread uses carbohydrates called arabinoxylans to form its structure. Many gluten-free breads use xanthan gum to approximate gluten-like elasticity and a mixture of gluten-free flours. They still rise before baking, and the best of them even taste like bread.
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