Bread: Encyclopedia II - Bread - Composition and Chemistry

Bread - Composition and Chemistry

Bread - Formulation

The amount of water and flour are the most significant measurements in a bread recipe, as they affect texture and crumb the most. Professional bakers use a system of percentages known as Bakers' Percentage in their recipe formulations, and measure ingredients by weight instead of by volume. Measurement by weight is much more accurate and consistent that measurement by volume, especially for the dry ingredients.

Flour is always 100%, and the rest of the ingredients are a percent of that amount by weight. Common table bread in the U.S. uses approximately 50% water, resulting in a finely textured, light, bread. Most artisan bread formulas contain anywhere from 60 to 75% water. In yeast breads, the higher water percentages result in more CO₂ bubbles, and a coarser bread crumb. One pound of flour will yield a standard loaf of bread, or two french loaves.

Bread - Flour

Flour is a product made from grain that has been ground into a powdery consistency. It is flour that provides the primary structure to the final baked bread. Commonly available flours are made from rye, barley, maize, and other grains, but it is wheat flour that is most commonly used for breads. Each of these grains provides starch and protein to the final product.

Wheat flour in addition to its starch contains three water soluble proteins groups, albumin, globulin, proteoses, and two non-water soluble proteins groups, glutenin and gliadin. When flour is mixed with water the water-soluble proteins dissolve, leaving the glutenin and gliadin to form the structure of the resulting dough. When worked by kneading, the glutenin forms strands of long thin chainlike molecules while the shorter gliadin forms bridges between the stands of glutenin. The resulting networks of strands produced by these two proteins is known as gluten.

Bread - Liquids

Water, or some other liquid, is used to form the flour into a paste or dough. The volume of liquid required varies between recipes, but a ratio of 1 cup of liquid to 3 cups of flour is common for yeast breads while recipes that use steam as the primary leavening method may have a liquid content in excess of one part liquid to one part flour by volume. In addition to water, other types of liquids that may be used include dairy products, fruit juices, or beer. In addition to the water in each of these they also bring additional sweeteners, fats, and or leavening components.

Bread - Leavening

Leavening is the process of adding gas to a dough before baking to produce a lighter, more easily chewed bread. Most bread consumed in the West is leavened. But there is also unleavened bread which has important symbolic use in Judaism (Matzo) and is used by some Christian churches.

A simple technique for leavening bread is the use of gas-producing chemicals. There are two common methods. The first is to use baking powder or a self-rising flour that includes baking powder. The second is to have an acidic ingredient such as buttermilk and add baking soda. The reaction of the acid with the soda produces gas.

Chemically-leavened breads are called quick breads and soda breads. This technique is commonly used to make muffins and sweet breads such as banana bread.

Many breads are leavened by the fungus yeast. The yeast ferments carbohydrates in the flour and any sugar, producing carbon dioxide. Most commercial and home bakers in the U.S. leaven their doughs with baker's yeast. Baker's yeast produces uniform, quick, and reliable results.

Both the baker's yeast, and the sourdough method of baking bread follow the same pattern. Water is mixed with flour, salt and the leavening agent (baker's yeast or sourdough starter). Other additions (spices, herbs, fats, seeds, fruit, etc.) are not necessary to bake bread, but often used. The mixed dough is then allowed to rise one or more times (a longer rising time results in more flavor, so bakers often punch down the dough and let it rise again), then loaves are formed and (after an optional final rising time) the bread is baked in an oven.

Many breads are made from a straight dough, which means that all of the ingredients are combined in one step, and the dough baked after the rising time. Alternatively, doughs can be made with the starter method, when some of the flour, water, and the leavening are combined a day or so ahead of baking, and allowed to ferment overnight. (Such as the poolish typically used for baguettes) On the day of the baking, the rest of the ingredients are added, and the rest of the process is the same as that for straight doughs. This produces a more flavorful bread with better texture. Many bakers see the starter method as a compromise between the highly reliable results of baker's yeast, and the flavor/complexity of a longer fermentation. It also allows the baker to use only a minimal amount of baker's yeast, which used to be scarce and expensive when it first became available.

The sour taste of sourdoughs actually comes not from the yeast, but from a lactobacillus, with which the yeast lives in symbiosis. The lactobacillus feeds on the byproducts of the yeast fermentation, and in turn makes the culture go sour by excreting lactic acid, which protects it from spoiling (since most microbes are unable to survive in an acid environment). All breads used to be sourdoughs, and the leavening process was not understood until the 19th century, when with the advance of microscopes, scientists were able to discover the microbes that make the dough rise. Since then, strains of yeast have been selected and cultured mainly for reliability and quickness of fermentation. Billions of cells of these strains are then packaged and marketed as "Baker's Yeast". Bread made with baker's yeast is not sour because of the absence of the lactobacillus. Bakers around the world quickly embraced baker's yeast for it made baking simple and so allowed for more flexibility in the bakery's operations. It made baking quick as well, allowing bakeries to make fresh bread from scratch as often as three times a day. While European bakeries kept producing sourdough breads, in the U.S., sourdough baking was widely replaced by baker's yeast, and only recently has that country (or parts of it, at least) seen the rebirth of sour-vinegar dough in artisan bakeries.

Sourdough breads are most often made with a sourdough starter (not to be confused with the starter method discussed above). A sourdough starter is a culture of yeast and lactobacillus. It is essentially a dough-like or pancake-like flour/water mixture in which the yeast and lactobacillifungus live. A starter can be maintained indefinitely by periodically discarding a part of it and refreshing it by adding fresh flour and water. (When refrigerated, a starter can go weeks without needing to be fed.) There are starters owned by bakeries and families that are several human generations old, much revered for creating a special taste or texture. Starters can be obtained by taking a piece of another starter and growing it, or they can be made from scratch. There are hobbyist groups on the web who will send their starter for a stamped, self-addressed envelope, and there are even mailorder companies that sell different starters from all over the world. An acquired starter has the advantage to be more proven and established (stable and reliable, resisting spoiling and behaving predictably) than from-scratch starters.

There are other ways of sourdough baking and culture maintenance. A more traditional one is the process that was followed by peasant families throughout Europe in past centuries. The family (usually the woman was in charge of breadmaking) would bake on a fixed schedule, perhaps once a week. The starter was saved from the previous week's dough. The starter was mixed with the new ingredients, the dough was left to rise, then a piece of it was saved (to be the starter for next week's bread). The rest was formed into loaves which were marked with the family sign (this is where today's decorative slashing of bread loaves originates from), and taken to the communal oven to bake. These communal ovens over time evolved into what we know today as bakeries, when certain people specialized in bread baking, and with time enhanced the process so far as to be able to mass produce cheap bread for everyone in the village.

The most famous sourdough bread made in the U.S. is the San Francisco Sourdough. It is a white bread, characterized by a pronounced sourness (not all sourdoughs are as sour as the San Francisco Sourdough), so much so that the dominant strain of lactobacillus in sourdough starters was named lactobacillus sanfrancisco.

The rapid expansion of steam produced during baking leavens the bread, which is as simple as it is unpredictable. The best known steam-leavened bread is the popover. Steam-leavening is unpredictable since the steam isn't produced until the bread is baked.

Steam leavening happens regardless of the rising agents (soda powder, yeast, baking-powder, sour dough, egg snow…)

• The rising agent generates carbon dioxide - or already contains air bubbles.
• The heat vaporises the water from the inner surface of the bubbles within the dough.
• The steam expands and makes the bread rise.

It is actually the main factor in the rise. CO₂ generation, on its own, is too small to account for the rise. Heat kills bacteria or yeast at an early stage, so the CO₂ generation is stopped.

Salt-risen bread employs a form of bacterial leavening that does not require yeast. Although the leavening action is not always consistent, and requires close attention to the incubating conditions, this bread is making a comeback due to its unique cheese-like flavor and fine texture. [1].

Bread - Fats or shortenings

Fats such as butter, vegetable oils, lard, or that contained in eggs affects the development of gluten in breads by coating and lubricating the individual strands of protein and also helping hold the structure together. If too much fat is included in a bread dough, the lubrication effect will cause the protein structures to divide. A fat content of approximately 3% by weight is the concentration that will produce the greatest leavening action.

In addition to their effects on leavening, fats also serve to tenderize the breads they are used in and also help to keep the bread fresh longer after baking.

Adapted from the Wikipedia article "Composition and Chemistry", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki