The principle of all leavening is the expansion by heat of some gas which is thoroughly mixed through the batter or dough. In cooking, there are three agents which are com- monly used in leavening doughs. The first of these is water vapor or steam. This, as in the pop-overs, is manu- factured from the water present in the batter by the heat of the oven. Then further heat expands the steam still more. At the same time the heat hardens the expanded gluten, so that after a while no further stretching is pos- sible. This explains why muffins and cake rise in the oven only at the beginning of the baking. The second agent is air. This is mixed in a batter in two ways, — it may be entangled in the batter itself by beating rapidly, or it may be beaten into egg and then folded into the batter. Even snow may be folded in like egg and introduce some air into the mixture. When the batter full of tiny bubbles of air is heated, this air expands and, stretching the gluten by which it is held, it makes larger holes, thus leavening all the mass and making it rise. Carbon dioxide is the third agent. This may be forced into the dough, a process, however, which is never used at home and rarely elsewhere. Carbon dioxide is, instead, manufactured in the dough itself. When yeast is put into bread, one is really starting a plant to grow. The plant feeds mainly on sugar. If cane sugar is present, it turns it first into glucose and fructose sugars and then 222 FOOD STUDY breaks them up into carbon dioxide and alcohol. The heat of the oven acts on carbon dioxide exactly as it does on water vapor or steam, expanding it into larger bubbles. As alcohol is more easily turned into vapor than is water, it becomes a gas and, expanding, helps in the leavening process. The other method of introducing carbon dioxide into doughs and batters will be shown in the next lesson. QUESTIONS 1. What effect has heat on gluten? 2. What other proteins are hardened by heat ? 3. After pop-overs are thoroughly baked, as they cool, what becomes of the steam ? Why are they better eaten hot ? Compare them to baked potatoes in this respect. 4. Why does an insufficiently cooked pop-over fall, when it is taken out of the oven ? 5. Calculate the cost of pop-overs. How do they compare with the cost of the bread that they would replace in a meal ? XLVI SOUR MILK GRIDDLECAKES Class Experiments. SODA AS A LEAVENING AGENT. 1. To find out why soda makes cakes light. Add a teaspoon of vinegar to a pinch of soda in a test tube. Tip the tube and hold the mouth of this test tube just above another containing a teaspoon of lime water. After a moment, cover the mouth of the lime-water tube and shake it. What is present ? What caused the bubbles in the first tube? SOUR MILK GRIDDLECAKES 223 2. What kind of substances must be put with soda to produce this gas ? a. Dip a piece of blue litmus paper into vine- gar and note the effect on the paper. Hold it in the fumes of ammonia, an alkaline sub- stance, and see the result. b. Now test the following and determine whether they are acid, alkaline, or neutral (neither acid nor alkaline) : 1 — water. 2 — sour milk. 3 — sweet milk. 4 — molasses and water. 5 — cream of tartar dissolved in hot water. 6 — thin starch paste. 7 — soda and water.

AI-modernized reading of the original text

The principle of all leavening is the expansion by heat of some gas which is thoroughly mixed through the batter or dough. In cooking, there are three agents which are commonly used in leavening doughs. The first of these is water vapor or steam. This, as in the pop-overs, is manufactured from the water present in the batter by the heat of the oven. Then further heat expands the steam still more. At the same time the heat hardens the expanded gluten, so that after a while no further stretching is possible. This explains why muffins and cake rise in the oven only at the beginning of the baking. The second agent is air. This is mixed in a batter in two ways, — it may be entangled in the batter itself by beating rapidly, or it may be beaten into egg and then folded into the batter. Even snow may be folded in like egg and introduce some air into the mixture. When the batter full of tiny bubbles of air is heated, this air expands and, stretching the gluten by which it is held, it makes larger holes, thus leavening all the mass and making it rise. Carbon dioxide is the third agent. This may be forced into the dough, a process, however, which is never used at home and rarely elsewhere. Carbon dioxide is, instead, manufactured in the dough itself. When yeast is put into bread, one is really starting a plant to grow. The plant feeds mainly on sugar. If cane sugar is present, it turns it first into glucose and fructose sugars and then breaks them up into carbon dioxide and alcohol. The heat of the oven acts on carbon dioxide exactly as it does on water vapor or steam, expanding it into larger bubbles. As alcohol is more easily turned into vapor than is water, it becomes a gas and, expanding, helps in the leavening process. The other method of introducing carbon dioxide into doughs and batters will be shown in the next lesson. 1. What effect has heat on gluten? 2. What other proteins are hardened by heat ? 3. After pop-overs are thoroughly baked, as they cool, what becomes of the steam ? Why are they better eaten hot ? Compare them to baked potatoes in this respect. 4. Why does an insufficiently cooked pop-over fall, when it is taken out of the oven ? 5. Calculate the cost of pop-overs. How do they compare with the cost of the bread that they would replace in a meal ? SOUR MILK GRIDDLECAKES Class Experiments. SODA AS A LEAVENING AGENT. 1. To find out why soda makes cakes light. Add a teaspoon of vinegar to a pinch of soda in a test tube. Tip the tube and hold the mouth of this test tube just above another containing a teaspoon of lime water. After a moment, cover the mouth of the lime-water tube and shake it. What is present ? What caused the bubbles in the first tube? SOUR MILK GRIDDLECAKES 223 2. What kind of substances must be put with soda to produce this gas ? a. Dip a piece of blue litmus paper into vinegar and note the effect on the paper. Hold it in the fumes of ammonia, an alkaline substance, and see the result. b. Now test the following and determine whether they are acid, alkaline, or neutral (neither acid nor alkaline) : 1 — water. 2 — sour milk. 3 — sweet milk. 4 — molasses and water. 5 — cream of tartar dissolved in hot water. 6 — thin starch paste. 7 — soda and water.

Food study