29.3 Flour in baking: gluten

Flour is the base of bread, cakes and pastries, whether they rise with yeast or with chemical leaveners. It is "the skeleton, which supports the other ingredients in a baked product".

Protein becomes gluten

A flour's strength depends on both how much protein it has and how good that protein is, and flours differ widely. Good protein gives a strong, stable flour. Even so, how a bread turns out depends on handling the dough well during fermentation so the gluten develops.

For bread, flour from hard spring wheat is thought best, because it has more good gluten than soft wheat flour. Mills often blend hard spring with hard winter wheat to get the strengths of both. A good bread flour has about 13% gluten.

Storing flour

Flour is not a potentially hazardous food: it does not support the growth of disease-causing bacteria the way moist foods do. It still needs a proper dry store.

How a dry storeroom is set up and rotated, first in, first out, is covered with food safety. see chapter 2: Rotation: first in, first out

• A dry storeroom should be dry and cool, ideally between 10°C and 15°C (50°F and 59°F).
• Flour keeps best at about 60% relative humidity. In a damp room above 23°C (74°F), mold, bacteria and fast spoilage take hold.
• Seal every opening in walls, ceiling and floor against rodents and vermin, and keep shelving at least 15 cm (6 in.) off the floor, with nothing stored on the floor itself.
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• Flour picks up smells and holds on to them, so the room must be well aired, and flour should not share space with onions, garlic, coffee or cheese.
• Store dry foods above wet foods.

Flour also dries out over a long stay in a dry store, and that changes the dough. A 40 kg (88 lb.) sack at 14% moisture can drop to 39 kg (86 lb.). That lost kilogram (2 lb.) of water has to be added back when you mix.

Testing flour

Flour from a reliable mill, milled and blended by modern methods, is fairly even all year and should not need testing. Even so, bakers and students should know how flours differ and how they are usually tested. The main bakeshop tests look at color, absorption, gluten strength and baking quality. Laboratories also test for albumen, starch, sugar, dextrin, minerals and fat.

Color. Flour color carries through to the bread, provided fermentation has gone properly; malt, brown sugar, molasses, salt and colored margarine in the dough also change the color. To compare a flour with one of known grade:

• Put a little of each flour side by side on a smooth sheet of glass.
• Work each with a spatula into a firm, smooth patch about 5 cm (2 in.) square, about 2 cm (4/5 in.) thick at the back and thinning to a film at the front.
• Compare the dry patches. Creamy white means a hard flour with good gluten. Dark or grayish means poor flour or dirt. Specks of bran mean a low grade.
• Dip the glass at an angle into clean water and let it partly dry. Color differences and bran specks show up more clearly when damp.

Absorption. Flours soak up different amounts of water, so the same formula gives doughs of different firmness. Most flours absorb between 55% and 65%. To measure it, weigh out 100 g (4 oz.) of flour and stir in water from a measured supply until the dough feels right, finishing by hand. Weigh what water is left, and divide the water used by the flour used. If 60 g of water went into 100 g of flour, the absorption is 60%.

Feel. Hard wheat flour takes up more liquid than soft. Rubbed between thumb and fingers, a good hard flour feels a little gritty; a soft, smooth feel points to soft flour or a soft and hard blend. Squeeze some in the hollow of your hand: hard flour holds the shape but crumbles as soon as it is touched, while soft flour stays in a lump.

Gluten strength. Hard flour has more gluten, and better gluten, than soft flour, and two hard flours can differ with the weather and where the wheat grew. A laboratory measures this exactly; a gluten ball gives a rough comparison.

• Take 250 g (9 oz.) each of a hard flour and an all-purpose flour, in two bowls.
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• Add enough water to make each a stiff dough, and mix until smooth. Rest the doughs about 10 minutes.
• Knead each dough under cold running water until the water runs clear and the starch is gone. Set a flour sieve in the sink so no dough goes down the drain. What is left is crude gluten.
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• Roll the gluten into balls and bake them on a pan lined with paper for about an hour at 215°C (420°F).
• The hard flour's ball comes out bigger, showing how its extra gluten gives more volume.
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Ash content. Ash is what would remain if 100 g of flour were burned. A high ash figure means the flour still holds more of the bran, the germ and the outer layer of endosperm; a low one means a more refined flour with a lower extraction rate.

Baking quality. The final test of any flour is the bread it makes. Good volume goes with good gluten. Poor volume points to young, or green, flour. A flour that cannot hold up through the whole fermentation may give a small, flat loaf. More yeast sometimes helps such a flour, because fermentation is shorter and the dough stays in better shape while it proofs in the pan.