32.3 Salt and fermentation in dough

Salt's kinds and what it does to food in general are covered earlier. see chapter 20: What salt does in food In a yeast dough it has particular jobs and particular rules.

How much salt

A dough usually takes about 1.75% to 2.25% salt, measured against the weight of the flour. For 1,000 g of flour, that is 17.5 g to 22.5 g. Some authorities work from the water instead, at about 30 g of salt per liter (1 oz. per quart).

In hot summer weather, many bakers add a little more salt than in winter, to guard the dough against unwanted changes while it ferments.

Keep salt and yeast apart

Salt and gluten

Salts strengthen the gluten network. That goes for table salt and for the calcium and magnesium salts in hard water. In sponge doughs and liquid fermentation systems, a little salt in the first stage firms up the gluten. Fats and emulsifiers work the other way: they coat the proteins.

Where the yeast's sugar comes from

The yeast in most bread is Saccharomyces cerevisiae, baker's yeast. It eats the sugars in the dough and makes carbon dioxide and ethanol, which raise the dough both while it ferments and when it first goes into the oven. The chemistry of that change is in the fermentation chapter. see chapter 26: Alcohol and gas

Most of the sugar comes from the starch in the flour, which is made of two large molecules, amylose and amylopectin. Yeast cannot use starch as it is; it must first be broken down into simple sugars. Once flour, yeast and water are mixed, enzymes from the wheat and from the yeast start this work, and they keep at it into the baking.

• Wheat flour has two kinds of amylase, enzymes that split starch. One cuts the starch chain at random places into shorter pieces. The other snips off maltose, a double sugar, from the end of the chain.
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• Yeast brings its own enzymes. Invertase splits several small sugars, and maltase splits maltose into two simple sugars.
• Flour improvers sometimes carry extra amylase into the dough.
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How gluten forms

Protein makes up about 10% to 15% of flour. Two groups matter most: the glutenins and the gliadins. When water is added, the glutenins take it up, swell, and become stretchy and flexible.

Before kneading, these two proteins stay separate. As the dough is mixed and kneaded, enzymes from the wheat cut the glutenin into smaller pieces, and glutenin and gliadin start to link to each other. The result is a web of protein called gluten. Starch granules get caught in it, and kneading works air in.

Bread dough has to be stretchy enough to relax when it rests, and to swell and hold gas when it rises, while still keeping its shape. Different doughs want different amounts of gluten.

• Bread needs a web strong enough to trap the gas, yet loose enough to let it expand.
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• Pizza dough needs very strong gluten, so it can be pulled thin without tearing.
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• Cookies are usually crumbly and hardly rise.

In the oven the yeast goes on fermenting for a while, until the heat kills it.

The crust: browning

When sugars and amino compounds are heated together, a chain of browning reactions called the Maillard reactions begins. No enzymes are involved. They make many flavors, among them malty, toasted, bready and nutty ones. Some of the families of aroma compounds they build are these: