Gluten
The seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination. Gluten 麵筋 (from Latin gluten, "glue") is a protein composite found in foods processed from wheat and related grain species. The prolamin and glutelin from wheat constitute about 80% of the protein contained in wheat seed. Gluten content has been implicated as a factor in the staling of bread, possibly because it binds water through hydration.
Gluten forms when glutenin ( only soluble in dilute acids or alkalis) molecules cross-link to form a sub-microscopic network attached to gliadin (alcohol-soluble). It gives elasticity to dough, helping it rise and keep its shape and often gives the final product a chewy texture. True gluten, with gliadin and glutenin, is limited to certain members of the grass family. The stored proteins of maize and rice are sometimes called glutens, but their proteins differ from true gluten.
Flour
Flour is a powder which is made by grinding cereal grains, other seeds or roots. Flour contains a high proportion of starches, which are a subset of complex carbohydrates also known as polysaccharides. Baking coagulates the gluten, which, along with starch, stabilizes the shape of the final product. The higher the protein content the harder and stronger the flour, and the more it will produce crusty or chewy breads. The lower the protein the softer the flour, which is better for cakes, cookies, and pie crusts.
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.
Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size: rice starch is relatively small (about 2μm) while potato starches have larger granules (up to 100μm). Pure starch is a white, tasteless and odourless powder that is insoluble in cold water or alcohol. "Oobleck" or "ooze", suspension of starch (e.g. cornstarch) in water, is a non-Newtonian fluid. In a Newtonian fluid, the relation between the shear stress and the shear rate is linear, passing through the origin, the constant of proportionality being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different, and can even be time-dependent. Therefore, a constant coefficient of viscosity cannot be defined.
Starch becomes soluble in water when heated. The granules swell and burst, the semi-crystalline structure is lost and the smaller amylose molecules start leaching out of the granule, forming a network that holds water and increasing the mixture's viscosity. This process is called starch gelatinization. During cooking, the starch becomes a paste and increases further in viscosity. During cooling or prolonged storage of the paste, the semi-crystalline structure partially recovers and the starch paste thickens, expelling water. This is mainly caused by retrogradation of the amylose.
Rice flour (粘米粉) is ground kernels of rice. It does not contain gluten. It is distinct from rice starch, which is usually produced by steeping rice in lye.
Wheat flour varieties are called "clean," "white," or "brown" ("strong", "hard") if they have high gluten content, and they are called "soft" or "weak" flour if gluten content is low.
The seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination. Gluten 麵筋 (from Latin gluten, "glue") is a protein composite found in foods processed from wheat and related grain species. The prolamin and glutelin from wheat constitute about 80% of the protein contained in wheat seed. Gluten content has been implicated as a factor in the staling of bread, possibly because it binds water through hydration.
Gluten forms when glutenin ( only soluble in dilute acids or alkalis) molecules cross-link to form a sub-microscopic network attached to gliadin (alcohol-soluble). It gives elasticity to dough, helping it rise and keep its shape and often gives the final product a chewy texture. True gluten, with gliadin and glutenin, is limited to certain members of the grass family. The stored proteins of maize and rice are sometimes called glutens, but their proteins differ from true gluten.
Flour
Flour is a powder which is made by grinding cereal grains, other seeds or roots. Flour contains a high proportion of starches, which are a subset of complex carbohydrates also known as polysaccharides. Baking coagulates the gluten, which, along with starch, stabilizes the shape of the final product. The higher the protein content the harder and stronger the flour, and the more it will produce crusty or chewy breads. The lower the protein the softer the flour, which is better for cakes, cookies, and pie crusts.
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by glycosidic bonds. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.
Starch molecules arrange themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size: rice starch is relatively small (about 2μm) while potato starches have larger granules (up to 100μm). Pure starch is a white, tasteless and odourless powder that is insoluble in cold water or alcohol. "Oobleck" or "ooze", suspension of starch (e.g. cornstarch) in water, is a non-Newtonian fluid. In a Newtonian fluid, the relation between the shear stress and the shear rate is linear, passing through the origin, the constant of proportionality being the coefficient of viscosity. In a non-Newtonian fluid, the relation between the shear stress and the shear rate is different, and can even be time-dependent. Therefore, a constant coefficient of viscosity cannot be defined.
Starch becomes soluble in water when heated. The granules swell and burst, the semi-crystalline structure is lost and the smaller amylose molecules start leaching out of the granule, forming a network that holds water and increasing the mixture's viscosity. This process is called starch gelatinization. During cooking, the starch becomes a paste and increases further in viscosity. During cooling or prolonged storage of the paste, the semi-crystalline structure partially recovers and the starch paste thickens, expelling water. This is mainly caused by retrogradation of the amylose.
- Plain or all-purpose flour does not have a leavening agent.
- Self-rising (or self-raising) flour is sold premixed with chemical leavening agents. The added ingredients are evenly distributed throughout the flour which aids a consistent rise in baked goods. This flour is generally used for preparing scones, biscuits, muffins, etc.
Corn (maize) flour should never be confused with cornstarch, which is known as "cornflour" in British English. Coarse whole-grain corn flour is usually called corn meal.
Corn starch, cornstarch, cornflour or maize starch is the starch of the corn (maize) grain obtained from the endosperm of the corn kernel. It is used as a thickening agent in soups and liquid-based foods. Corn starch is sometimes preferred over flour because it forms a translucent mixture, rather than an opaque one.
Tapioca Starch/ Tapioca Flour/ Potato Starch (木薯粉/泰國生粉/太白粉) is obtained by grinding the tubers of potato to a pulp and removing the fibre and protein by water-washings. It is very white starch powder used as a thickening agent. Standard potato starch needs boiling, to thicken in water, giving a transparent gel. 食物放涼之後，茨汁會變得較稀，因此一般整蛋糕/做西點多利用粟粉來達到粘稠的特性而不使用太白粉。
Corn starch, cornstarch, cornflour or maize starch is the starch of the corn (maize) grain obtained from the endosperm of the corn kernel. It is used as a thickening agent in soups and liquid-based foods. Corn starch is sometimes preferred over flour because it forms a translucent mixture, rather than an opaque one.
Tapioca Starch/ Tapioca Flour/ Potato Starch (木薯粉/泰國生粉/太白粉) is obtained by grinding the tubers of potato to a pulp and removing the fibre and protein by water-washings. It is very white starch powder used as a thickening agent. Standard potato starch needs boiling, to thicken in water, giving a transparent gel. 食物放涼之後，茨汁會變得較稀，因此一般整蛋糕/做西點多利用粟粉來達到粘稠的特性而不使用太白粉。
Glutinous rice flour (糯米粉) or sticky rice flour, used in east and southeast Asian cuisines for making tangyuan, etc.
Rice flour (粘米粉) is ground kernels of rice. It does not contain gluten. It is distinct from rice starch, which is usually produced by steeping rice in lye.
Wheat flour varieties are called "clean," "white," or "brown" ("strong", "hard") if they have high gluten content, and they are called "soft" or "weak" flour if gluten content is low.
- Cake flour (低筋麵粉) is a finely milled white flour made from soft wheat. It has very low protein content, between 8% - 10%, making it suitable for soft-textured cakes and cookies. 適合用來做糕點、雪芳蛋糕、笑口棗、鍋餅等
- Pastry flour or cookie flour or cracker flour has slightly higher protein content than cake flour but lower than all-purpose flour. Its protein content ranges between 9% - 10%. It is suitable for pie pastry and tarts, some cookies, muffins, biscuits and other quick breads.
- All-purpose or plain flour (中筋麵粉) is a blended wheat flour with a protein content lower than bread flour, ranging 9% - 12%. The increased protein binds to the flour to entrap carbon dioxide released by the yeast fermentation process, resulting in a stronger rise. 大部分中式點心都是以中筋粉來製作的。
- Bread flour or strong flour (高筋麵粉) is always made from hard wheat, usually hard spring wheat. It has a very high protein content, between 10% - 13%, making it excellent for yeast bread baking. 適合用來做麵包、派皮、鬆餅、餃子皮、麵條等
- Tang flour or wheat starch (澄麵/無筋面粉)) is a type of wheat flour used primarily in Chinese cooking for making the outer layer of dumplings and buns. 澄麵是從小麥萃取澱粉所製成，是一種完全不含蛋白質的麵粉，因此缺乏黏合力，需加入熱水讓部份澄麵中的澱粉糊化，才可和其他澄麵結合起來。澄麵糰成型之後，若用刀將皮拉薄，就是廣式點心常見的澄麵皮，可用來做蝦餃、水晶皮等，蒸熟後餡枓若隱若現，看起來晶瑩剔透。
