10. Cooking Temperatures Of Different Starches. Experiment: Cooking Starch

Pare and grate one or more potatoes. Wash the gratings by placing them in a cheesecloth bag and immersing them in cold water. Squeeze and press the contents of the bag until no more starch seems to pass through the cloth. Let it settle, pour off the water; add clear water and let the starch settle again. Pour off the second water. Take one tablespoonful of the starch, mix it with one cupful of cold water. Heat it slowly over a moderate fire, stirring it constantly, and recording the temperature at which the mixture becomes noticeably clearer and thickens.

Repeat this experiment with corn-starch; wheat starch, washed from wheat flour, as is done with the grated potato; with starch washed from rye flour; and, if desired, with rice, bean, pea, oat and tapioca starches, also.

"Food and the Principles of Dietetics," by Hutchison, gives, on page 378, a list of different starches and the temperatures at which they gelatinize.

In a bulletin entitled "Digestibility of Starch of Different Sorts as Affected by Cooking," by Edna D. Day, Ph.D. (U. S. Dept. of Agriculture, Office of Experiment Stations, Bulletin No. 202, page 40), we read that starch takes up water at 60 degrees to 80 degrees Centigrade (140 degrees to 176 degrees Fahrenheit) and forms a sticky, colloidal substance known as starch paste, in which form it is very easily digested.

Long boiling, at least to the extent of three hours, does not make it more quickly digestible. There is something to be considered besides the mere starch in cooking starchy foods, and the fact that potato starch will form paste at 149 degrees while rice starch requires 176 degrees does not mean that less cooking will be needed for potatoes than for rice. The woody fibre or other constituents of foods, as well as their density and difference in size, must be taken into account.

11. Cooking Temperatures Of Proteids. Egg Albumen

In the bulletin entitled "Eggs and Their Uses as Food," by C. F. Langworthy, Ph.D., published as Farmers' Bulletin, No. 128, by the U. S. Department of Agriculture, the statement is made that "egg white begins to coagulate at 134 degrees Fahrenheit. White fibres appear which become more numerous until at about 160 degrees Fahrenheit the whole mass is coagulated, the white almost opaque, yet it is tender and jelly-like. If the temperature is raised to 212 degrees Fahrenheit, and continued, the coagulated albumen becomes much harder and eventually more or less tough and horn-like; it also undergoes shrinkage. It has been found by experiment that the yolk of egg coagulates firmly at a lower temperature than the white."

It also says that these changes in the albumen suggest the idea that it is not advisable to cook eggs in boiling water in order to secure the most desirable result.

Experiment A: To Show The Changes That Take Place In Egg White At Various Temperatures

Materials

Test-tube and holder Beaker or saucepan of water

Thermometer Egg white

Put the white of egg into the test-tube. Insert the thermometer. Hold the test-tube in the pan of cold water to the depth of the egg white. Gradually heat the water and observe the temperature at which the first change in the egg albumen takes place. Notice also the temperature of the water at this point. Continue the experiment until the water in the outer vessel has boiled ten or twenty minutes, noting the temperatures at which the various changes occur.

Experiment B: To Show The Temperatures Obtained In The Proper Cooking Of Eggs

Materials

Fireless cooker Eggs

Water Thermometer

Cook eggs as directed for soft-cooked eggs on page 190, observing the temperature of the water after the eggs are added to it, and when they are removed from the cooker; also the condition, flavour, etc., of the eggs.

Cereal Proteids

Professor Harcourt, in his bulletin, "Breakfast Foods," published by the Ontario Department of Agriculture, pp. 20 and 29, says that long cooking of cereals renders the protein more digestible. The cooking which he describes was carried on in a double boiler, and, therefore, below boiling temperature, and in this respect is similar to fireless cookery. He says that while short cooking, which was done at boiling temperature, seemed to make cereal proteids less digestible, the long cooking at below boiling temperature, which followed, somewhat changed them and made them more digestible.

While little study appears to have been made of the digestibility of cereal proteids when cooked for a long time at a low temperature, it is probably fair, in the absence of further definite information, to assume that, like animal proteids, it is better to cook them at a low temperature such as that of the fireless cooker, than at the temperature of boiling water or higher.

Meat Proteids

In the bulletin entitled "A Precise Method of Roasting Meat," by Elizabeth A. Sprague and H. S. Grindley, published by the University of Illinois, a study is made of the temperatures at which the changes take place from raw meat to "rare"; from "rare" to "medium rare," and from this to "well done" meat. The authors found that if the centre of the meat is between 130 degrees and 148 degrees Fahrenheit (55 degrees and 65 degrees Centigrade), it is rare; if it is between 148 degrees and 158 degrees Fahrenheit (65 degrees and 70 degrees Centigrade), it is medium rare; and if it is between 158 degrees and 176 degrees Fahrenheit (70 degrees and 80 degrees Centigrade), it is well done. They found no advantage in cooking meat in a very hot oven (385 degrees Fahrenheit, or 195 degrees Centigrade), but rather a difficulty to keep it from burning; that in an oven which was about 350 degrees Fahrenheit (175 degrees Centigrade), the meat cooked better; and that in an Aladdin oven which kept the meat at about 212 degrees Fahrenheit (100 degree Centigrade), it cooked best of all; that is, it was of more uniform character all through, more juicy, and more high flavoured. This seems to point to an advantage in fireless cookery for meats, and practical experience bears it out. The initial heat of the insulated oven serves to sear and brown the meat, and when this heat is reduced by the cooling of the stones, the low temperature found to be best for completing the roasting is obtained. With regard to meats cooked in water in the cooker, experience has shown that they become well done and are more tender than when boiled, showing that the temperatures necessary to reach that degree of cooking are obtained even in the centre of a large piece of meat, without toughening or hardening the outside of the meat, as is done when more intense heat is applied.

The hardening effect of long cooking at a high temperature on meat proteids can be demonstrated by broiling a tender piece of steak until it is rare, cutting off a small piece, continuing the broiling for a few minutes, cutting off another piece and comparing these pieces with the remainder, which should be broiled until very well done.