Specialty whole-grain flours Specialty whole-grain flours

Soft white wheat

1011 1011

Specialty whole-grain flours Specialty whole-grain flours

Club wheat

89 89

Cake flours Cake flours

Durum wheat

1216 1216

Semolina for dried pasta Semolina for dried pasta

In addition to their cla.s.sification by protein content, North American wheats are named by their growth habit and kernel color. Spring wheats (including durum) are sown in the spring and harvested in the fall, while winter wheats are sown in late fall, live through the winter as a seedling, and are harvested in the summer. The most common wheat varieties are red, red, their seed coat reddish brown with phenolic compounds. their seed coat reddish brown with phenolic compounds. White White wheats, with a much lower phenolic content and a light tan seed coat, are becoming increasingly popular for the light color and less astringent "sweet" taste of their whole-wheat flours and products containing part or all of the bran. wheats, with a much lower phenolic content and a light tan seed coat, are becoming increasingly popular for the light color and less astringent "sweet" taste of their whole-wheat flours and products containing part or all of the bran.

Turning Wheat into Flour The baking qualities of a particular flour are determined by the wheat from which it's made, and how that wheat is turned into flour.

Wheat grain and flour. Left Left : The wheat kernel before milling. Its actual length is about a quarter of an inch/6 mm. : The wheat kernel before milling. Its actual length is about a quarter of an inch/6 mm. Upper right Upper right : Soft wheat flour. The protein in this kind of wheat comes in thin, weak sections interrupted by starch granules and air pockets. When milled, it produces small, fine particles. Soft flour makes a weak gluten and is preferred for tender pastries and cakes. : Soft wheat flour. The protein in this kind of wheat comes in thin, weak sections interrupted by starch granules and air pockets. When milled, it produces small, fine particles. Soft flour makes a weak gluten and is preferred for tender pastries and cakes. Lower right Lower right : Hard wheat flour. The protein matrix in hard wheat endosperm is strong enough to break off in chunks during milling. Hard flours make strong gluten and are preferred for most bread making. : Hard wheat flour. The protein matrix in hard wheat endosperm is strong enough to break off in chunks during milling. Hard flours make strong gluten and are preferred for most bread making.

Milling: Conventional and Stone Grinding Milling is the process of breaking the wheat kernel down into small particles, and sifting the particles to make a flour of the desired qualities. Most flours are Milling is the process of breaking the wheat kernel down into small particles, and sifting the particles to make a flour of the desired qualities. Most flours are refined refined: that is, they have been sieved to remove the germ and bran layers from the particles of protein-and starch-rich endosperm. Bran and germ are rich in nutrients and flavor, but they go rancid in a few weeks, and interfere physically and chemically with the formation of a continuous, strong gluten; so whole-grain flours make denser, darker breads and pastries. In conventional milling, grooved metal rollers shear open the grain, squeeze out the germ, and sc.r.a.pe the endosperm away to be ground, sieved, and reground until the particles reach the desired size. Stone grinding, which is much rarer, crushes the whole grain more thoroughly before sieving, so that some of the germ and bran end up in even the refined flours. Stone-ground flour is therefore more flavorful than conventionally milled flour, but also has a shorter shelf-life.

Improving and Bleaching Bakers have known for a long time that freshly milled flour makes a weak gluten, a slack dough, and a dense loaf. As the flour ages for a few weeks in contact with the air, its gluten and baking properties improve. We understand now that oxygen in the air gradually frees the glutenin proteins' end sulfur groups to react with each other and form ever longer gluten chains that give the dough greater elasticity. Beginning around 1900, millers began to save time, s.p.a.ce, and money by supplementing freshly milled flour with oxidizing chlorine gas and then with pota.s.sium bromate. However, worries about the potential toxicity of bromate residues in the late 1980s led most millers to replace bromate with as...o...b..c acid (vitamin C) or azodicarbonamide. (As...o...b..c acid itself is an antioxidant, but becomes oxidized to dehydroas...o...b..c acid, which in turn oxidizes the gluten proteins.) In Europe, fava bean flour and soy flour have been used as flour improvers; their active fat-oxidizing enzymes, which generate the typical beany flavor, also indirectly cause the oxidation and elongation of gluten proteins. Bakers have known for a long time that freshly milled flour makes a weak gluten, a slack dough, and a dense loaf. As the flour ages for a few weeks in contact with the air, its gluten and baking properties improve. We understand now that oxygen in the air gradually frees the glutenin proteins' end sulfur groups to react with each other and form ever longer gluten chains that give the dough greater elasticity. Beginning around 1900, millers began to save time, s.p.a.ce, and money by supplementing freshly milled flour with oxidizing chlorine gas and then with pota.s.sium bromate. However, worries about the potential toxicity of bromate residues in the late 1980s led most millers to replace bromate with as...o...b..c acid (vitamin C) or azodicarbonamide. (As...o...b..c acid itself is an antioxidant, but becomes oxidized to dehydroas...o...b..c acid, which in turn oxidizes the gluten proteins.) In Europe, fava bean flour and soy flour have been used as flour improvers; their active fat-oxidizing enzymes, which generate the typical beany flavor, also indirectly cause the oxidation and elongation of gluten proteins.

The traditional air-aging of flour had a visible side effect: the yellowish flour becomes progressively paler as the xanthophyll pigments are oxidized to a colorless form. Once the chemistry of this change was understood, millers began using bleaching agents (azodicarbonamide, peroxide) to whiten flours. Many bakers prefer to use unbleached flours because they have been subjected to less chemical alteration. Bleaching is not allowed in Europe.

Minor Flour Components The gluten proteins and starch granules in flour account for about 90% of flour weight, and for much of the behavior of flour doughs and batters. But some minor components have an important influence.

Extraction RatesThe degree to which a flour has been refined is designated by the "extraction rate," or the percentage of the whole grain remaining in the finished flour. Whole wheat flour has an extraction rate of 90%. Most commercial white flours contain between 70 and 72% of the whole grain; French bread flour ranges from 72 to 78%, and so carries more flavor of the whole grain. Home bakers can make their own higher-extraction refined flours by supplementing commercial white flour with a portion of whole wheat flour that they have sifted to remove coa.r.s.e bran and germ particles.

Fats and Related Molecules Although white flour is only about 1% fats, fat fragments, and phospholipids by weight, these substances are essential to the development of a well-raised bread. There's evidence that some fatty materials can help stabilize the dough bubble walls as they expand and prevent premature rupture and collapse. Others become attached to starch granules and help soften the bread structure and slow staling. Similar ingredients added by the cook or manufacturer can magnify these useful effects (p. 524). Although white flour is only about 1% fats, fat fragments, and phospholipids by weight, these substances are essential to the development of a well-raised bread. There's evidence that some fatty materials can help stabilize the dough bubble walls as they expand and prevent premature rupture and collapse. Others become attached to starch granules and help soften the bread structure and slow staling. Similar ingredients added by the cook or manufacturer can magnify these useful effects (p. 524).

Enzymes Since the flour's normal endowment of sugars is enough to feed yeast cells for only a short period of time, flour manufacturers have long supplemented the ground wheat with malted wheat or barley: grains that have been allowed to sprout and develop the enzymes that break down starch to sugars. Because malt flours give a dark cast to flours and doughs, and because their activity is somewhat variable, manufacturers are increasingly replacing them with enzymes extracted and purified from microscopic molds ("fungal amylase"). Since the flour's normal endowment of sugars is enough to feed yeast cells for only a short period of time, flour manufacturers have long supplemented the ground wheat with malted wheat or barley: grains that have been allowed to sprout and develop the enzymes that break down starch to sugars. Because malt flours give a dark cast to flours and doughs, and because their activity is somewhat variable, manufacturers are increasingly replacing them with enzymes extracted and purified from microscopic molds ("fungal amylase").

The Protein Contents of Common Wheat FloursThese figures are approximate, and a.s.sume that the flour contains 12% moisture. The bulk of flour weight, from 70 to 80%, is starch and other seed carbohydrates. High-protein flours absorb substantially more water than low-protein flours, and so will produce stiffer doughs with the same proportion of water.

Flour

Protein Content Protein Content

Whole wheat, graham

1115 1115

Durum semolina

13 13.

Bread

1213 1213

All-purpose (U.S. national brands)

1112 1112

All-purpose (U.S. regional brands, South, Pacific Northwest)

7.59.5 7.59.5

Pastry

89 89

Cake

78 78

0 or 00 (Italian soft wheat)

1112 1112

Type 55 (French blend of soft and hard wheat)

910 910

English plain

710 710

Vital gluten

7085 7085

Because different flours have not only different protein contents, but different protein qualities, it's not really possible to turn all-purpose flour into pastry flour or vice versa. However, it's possible to dilute the gluten proteins of a given flour by the addition of cornstarch or another pure starch, or strengthen them by adding powdered vital gluten. To approximate pastry flour with all-purpose, add one part by weight of starch to two parts of all-purpose flour; to approximate all-purpose flour with pastry flour, add one-quarter part of gluten to two parts of pastry flour. (Purified gluten loses a little less than half its strength in the drying process.) With its chlorine-altered starch and fats, cake flour is inimitable. Because different flours have not only different protein contents, but different protein qualities, it's not really possible to turn all-purpose flour into pastry flour or vice versa. However, it's possible to dilute the gluten proteins of a given flour by the addition of cornstarch or another pure starch, or strengthen them by adding powdered vital gluten. To approximate pastry flour with all-purpose, add one part by weight of starch to two parts of all-purpose flour; to approximate all-purpose flour with pastry flour, add one-quarter part of gluten to two parts of pastry flour. (Purified gluten loses a little less than half its strength in the drying process.) With its chlorine-altered starch and fats, cake flour is inimitable.

Kinds of Flour Though manufacturers and professional bakers can obtain flours from particular wheats, most flours for sale in supermarkets are labeled according to their intended use, with no direct indication of the kind of wheat or wheats they contain - they're usually a blend - or their protein content or quality. Flour compositions can vary significantly from region to region; "all-purpose" flour in much of the United States and Canada has a higher protein content than "all-purpose" flours in the South or Pacific Northwest. Not surprisingly, recipes developed with a particular flour often turn out very differently when made with another, unless care is taken to find a replacement that closely approximates the original. The box on p. 530 lists the compositions of common wheat flours.

Whole wheat flours are high in protein, but a significant fraction of that protein comes from the germ and aleurone layer and does not form gluten; and germ and bran particles interfere with gluten formation. They therefore tend to make dense but flavorful breads. Bread flours are high in strong gluten proteins, and give the lightest, highest, and chewiest loaf breads. Both pastry and cake flours have low levels of weak gluten protein for making tender baked goods. Cake flour is distinctive because it's treated with chlorine dioxide or chlorine gas. This treatment has several effects on the starch granules that are useful in cake making (p. 555), and leaves a trace of hydrochloric acid in the flour, which gives batters and doughs an acid pH and slightly acid taste.

"Self-rising" flours are flours that contain baking powder (11/2 teaspoons baking powder per cup flour/57 gm per 100 g), and therefore don't require added leavening for the making of quickbreads, pancakes, and other chemically raised foods. "Instant" or "instantized" flours (two brand names are Shake & Blend and Wondra) are low-protein flours whose starch granules have been precooked until they gelate, then dried again. The precooking and drying make it easier for water to penetrate them again during cooking. Instant flours are well suited to tender pastries and last-minute thickening of sauces and gravies. teaspoons baking powder per cup flour/57 gm per 100 g), and therefore don't require added leavening for the making of quickbreads, pancakes, and other chemically raised foods. "Instant" or "instantized" flours (two brand names are Shake & Blend and Wondra) are low-protein flours whose starch granules have been precooked until they gelate, then dried again. The precooking and drying make it easier for water to penetrate them again during cooking. Instant flours are well suited to tender pastries and last-minute thickening of sauces and gravies.

Dough and Batter Ingredients: Yeasts and Chemical Leavenings Leavenings are the ingredients that fill doughs and batters with bubbles of gas, thus reducing the amount of solid material in a given volume and making the bread or cake less dense, more light and tender.

Yeasts Humans have been eating raised breads for 6,000 years, but it wasn't until the investigations of Louis Pasteur 150 years ago that we began to understand the nature of the leavening process. The key is the gas-producing metabolism of a particular cla.s.s of fungus, the yeasts. The word "yeast," however, is as old as the language, and first meant the froth or sediment of a fermenting liquid that could be used to leaven bread.

Food Words: Leavening Leavening and and Yeast YeastLeavening comes from an Indo-European root meaning "light, having little weight." Related words from the same root include comes from an Indo-European root meaning "light, having little weight." Related words from the same root include levity, lever, relieve, levity, lever, relieve, and and lung. Yeast lung. Yeast comes from a root word that meant "to seethe, boil, bubble over." This derivation underlines the way in which fermentation seemed to be a kind of cooking of the cereal gruel, a transformation from within. comes from a root word that meant "to seethe, boil, bubble over." This derivation underlines the way in which fermentation seemed to be a kind of cooking of the cereal gruel, a transformation from within.

The yeasts are a group of microscopic single-celled fungi, relatives of the mushrooms. More than 100 different species are known. Some cause human infections, some contribute to food spoilage, but one species in particular - Saccharomyces cerevisiae, Saccharomyces cerevisiae, whose name means "brewer's sugar fungus" - is put to good use in both brewing and baking. For much of human history, yeast was simply recruited from the grain surface or supplied by an earlier piece of dough, or obtained from the surface of beer brewing vats. Today strains especially selected for breadmaking are grown on mola.s.ses in industrial fermentation tanks. whose name means "brewer's sugar fungus" - is put to good use in both brewing and baking. For much of human history, yeast was simply recruited from the grain surface or supplied by an earlier piece of dough, or obtained from the surface of beer brewing vats. Today strains especially selected for breadmaking are grown on mola.s.ses in industrial fermentation tanks.

Yeast Metabolism Yeasts metabolize sugars for energy, and produce carbon dioxide gas and alcohol as by-products of that metabolism. The overall equation for the conversion that takes place in yeast cells is this: Yeasts metabolize sugars for energy, and produce carbon dioxide gas and alcohol as by-products of that metabolism. The overall equation for the conversion that takes place in yeast cells is this: C6H12O6[image] 2C 2C2H5OH + 2CO2 (1 molecule of glucose sugar yields 2 molecules of alcohol plus 2 molecules of carbon dioxide) (1 molecule of glucose sugar yields 2 molecules of alcohol plus 2 molecules of carbon dioxide) In making beer and wine, the carbon dioxide escapes from the fermenting liquid, and alcohol acc.u.mulates. In making bread, both carbon dioxide and alcohol are trapped by the dough, and both are expelled from the dough by the heat of baking.

In an unsweetened dough, yeasts grow on the single-unit sugars glucose and fructose and on the double-glucose sugar maltose, which enzymes in the flour produce from broken starch granules. A small amount of added table sugar in a dough will increase yeast activity, while a large amount decreases it (see sweet breads, p. 546), as does added salt. Yeast activity is also strongly affected by temperature: the cells grow and produce gas most rapidly at about 95F/35C.

In addition to providing carbon dioxide gas to inflate the dough, yeasts release a number of chemicals that affect the dough consistency. The overall effect is to strengthen the gluten and improve its elasticity.

Forms of Baker's Yeast Commercial yeast is sold to home and restaurant cooks in three common forms, each a different genetic strain of Commercial yeast is sold to home and restaurant cooks in three common forms, each a different genetic strain of S. cerevisiae S. cerevisiae with different traits. with different traits.

Cake or compressed yeast is a moist block of fresh yeast cells, direct from the fermentation vat. Its cells are alive, and produce more leavening gas than the other forms. Cake yeast is perishable, must be kept refrigerated, and has a brief shelf life of one to two weeks.

Active dry yeast, which was introduced in the 1920s, has been removed from the fermentation tank and dried into granules with a protective coating of yeast debris. The yeast cells are dormant and can be stored at room temperature for months. The cook reactivates them by soaking them in warm water, 105110F/ 4143C, before mixing the dough. At cooler soaking temperatures, the yeast cells recover poorly and release substances that interfere with gluten formation (glutathione).

Instant dry yeast, an innovation of the 1970s, is dried more quickly than active dry yeast, and in the form of small porous rods that take up water more rapidly than granules. Instant yeast doesn't need to be prehydrated before mixing with other dough ingredients, and produces carbon dioxide more vigorously than active dry yeast.

An Unusual Chemical Leavening: HartshornThe leavening that doesn't involve an acid-base reaction is ammonium salts - ammonium carbonate and/or carbamate - which were once known as "hartshorn" because they were produced by the distillation of deer antlers. (Hartshorn was also a common source of gelatin.) When these compounds are heated to 140F/60C, they decompose into two leavening gases, carbon dioxide and ammonia, and don't produce water. They're especially suited to thin, very dry cookies and crackers with a large surface area to release the pungent ammonia during baking.

Baking Powders and Other Chemical Leaveners Yeast cells produce carbon dioxide slowly, over the course of an hour or more, so the material surrounding them must be elastic enough to contain it for that much time. Weak doughs and runny batters can't hold gas bubbles for more than a few minutes, and are therefore usually raised with a faster-acting gas source. This is the role played by chemical leavenings. These ingredients are concentrated, and small differences in the amount added can cause large variations in the quality of the finished food. Too little leavening will leave it flat and dense, while too much will cause the batter to overexpand and collapse into a coa.r.s.e structure with a harsh flavor.

Nearly all chemical leavenings exploit a reaction between certain acidic and alkaline compounds that results in the production of carbon dioxide, the same gas produced by yeast. The first chemical leavening was a dried water extract of wood ash - potash, mainly pota.s.sium carbonate - which reacts with the lactic acid in a soured dough as follows: 2(C3H6O3) + K2CO3[image]2(KC3H5O3)+ H2O + CO2(2 molecules of lactic acid plus 1 of pota.s.sium carbonate yield 2 molecules of pota.s.sium lactate, plus a molecule of water, plus a molecule of carbon dioxide) The Acid Components of Baking PowdersSome of these acids are available only to manufacturers. Most double-acting supermarket baking powders are a mixture of sodium bicarbonate, MCP, and SAS. Single-acting powders omit the SAS, and the MCP is coated to delay its release artificially.