EXPERIMENT 26: CHANGE OF STARCH INTO DEXTRIN.—Place a teaspoonful of flour in a frying pan and heat slowly until it becomes very dark brown and uniform in color. Put a little of the browned flour into a test tube, add water, then shake. Add a few drops of iodine. What indicates the presence of starch? Is starch present?

The starch has been changed to dextrin. Dextrin gives a purple (reddish blue) color when treated with iodine.

EXPERIMENT 27: THE SOLUBILITY OF DEXTRIN.—Pour the remainder of the browned flour from Experiment 26 into a test tube. Add water and shake. Pour through filter paper [Footnote 26: Liquids pass through filter paper, but solids do not. Hence if a mixture of solid and liquid is poured upon filter paper, the liquid passes through, but the solid remains on the paper.] into another test tube (see Figure 30). Notice the color of the liquid that has been filtered. Add a few drops of iodine to the filtered liquid. Is dextrin present? Is dextrin soluble in water? [Illustration: Figure 30.—Method of Folding Filter Paper.]

From these experiments, we find that dry heat has changed insoluble starch into a soluble substance called dextrin. Dextrin is found in small amounts in the crust of bread and in toast.

DIGESTION OF STARCH.—It was found in a previous lesson (Lesson XVI) that sugar is entirely soluble in water, and since digestion and solution are closely related, the digestion of some sugar is simple. Starch was found to be insoluble in cold water and only semi-soluble in hot water. In the process of digestion it would seem that some change must take place in the starch to make it soluble. Such a change does take place; starch is changed into a soluble carbohydrate or a sugar before it is digested.

Substances called enzymes which are in the saliva of the mouth [Footnote 27: Ptyalin and amylopsin are the ferments found in the mouth and intestines, respectively.] and in the digestive juices of the intestines [Footnote 28: Ptyalin and amylopsin are the ferments found in the mouth and intestines, respectively.] cause this change. To show that this change takes place to some extent in the mouth, try the following experiments:

EXPERIMENT 28: STARCH IN CRACKER.—Test a bit of cracker with iodine for starch. What indicates the presence of starch? Does the cracker contain starch?

EXPERIMENT 29: ACTION OF SALIVA UPON STARCH.—Thoroughly chew a bit of cracker. As you chew the cracker, note that it becomes sweeter in flavor. Remove from the mouth, and place upon a piece of paper. Test it with iodine. A purple (reddish blue) color indicates a soluble carbohydrate (see Experiment 27). What substance does the masticated cracker contain? Explain the change that has taken place in the cracker by mastication.

TOAST.—Bread is properly toasted when it is dried out thoroughly and then browned on the outside. Both the crumb and the crust of the toast are thus made crisp. Crisp toast crumbles during mastication.

Fresh bread contains much moisture. When it is toasted quickly, the moisture is inclosed in the interior of the slice and the resulting toast is very soft. This kind of toast is almost as difficult to digest as fresh bread. Instead of toast breaking into bits during digestion, it remains in a solid mass and is digested with difficulty.

Give at least two practical methods of toasting bread to produce the desired kind of toast.

CREAM TOAST

1 1/2 tablespoonfuls butter or substitute 1/2 teaspoonful salt 2 tablespoonfuls flour 2 cupfuls milk or cream 6 to 8 slices of toast

Heat the fat; when it bubbles, add the flour and salt, mixing thoroughly. Add a small portion of the milk. Heat and stir continually until it thickens. Add another portion of the milk and proceed as before. Continue until all the milk has been added. The sauce is sufficiently cooked when it reaches the boiling point after the last quantity of milk has been added. Pour this sauce over dry or moist toast.

Moist toast is prepared by dipping dry toast quickly into hot, salted water or hot milk. If the crust has not been cut from bread for toasting, only the outer edges of the toast may be moistened.

The flavor of butter in Cream Toast is pleasing. To secure some butter flavor and at the same time economize, a combination of butter and a mild flavored fat or oil may be used.

QUESTIONS

Give the reason for mixing flour and fat as directed in White Sauce (see
Experiment 25).

What is the proportion of fat and flour? What is the proportion of flour and liquid? Using this proportion, how much flour should be used for one cupful of liquid?

What is the use of flour in White Sauce?

Note the consistency of the sauce, and keep it in mind as a standard of comparison for the thickness of other sauces.

What should be the condition of the crumb of toast to be most quickly digested? Give reasons for your answer.