Experimental cookery

Tinkler and Soar have found that eggs cooked 15 minutes in boiling water and cooled slowly have some green color at the surface of the yolk; if cooled quickly, none or very little green color develops. Cooking in boiling water for 30 minutes gives a great deal of green color, no matter how the eggs are cooled. Since the yolk contains iron and a fairly large quantity of sulfur, they wondered why the entire yolk did not turn green when cooked as long as 7 hours. They found the sulfur compounds in the yolk were more stable and less easily broken down to form hydrogen sulfide. Thus even with long cooking the color of the interior of the yolk is not changed. Custards In custards, eggs are combined with milk and sugar. The chief protein of cow's milk is casein, which is not coagulable by heat. Milk contains some albumin and a small proportion of globulin, which are coagulable by heat. Zoller states that the protein coagulable by heat is about 0.75 per cent of cow's milk. In the mixed milk and egg, the egg furnishes the larger percentage of the heat-coagulable protein. As the egg, milk, and sugar mix- ture is heated, coagulation occurs, and the thickened mixture is known as custard. If the temperature of the custard is carried a little higher than the coagulation point, a point is reached at which the custard begins to show syneresis, or the liquid separates from the curd. This is called the curdling point. Baked and soft custards. Custards may be cooked in two ways. They may be cooked without stirring. This type is usually baked in the oven and is called baked custard. The other tj^pe of custard is stirred continually while it is cooked and is called soft custard. If the proportion of ingredients in the custard are the same the one cooked without stirring is firmer in texture and appears to be in one piece or clot. The soft custard has a softer texture and is not in one piece but is a viscous fluid. The stirred custard also tends to curdle more readily than the baked 344 EGG COOKERY custard. In part, this is undoubtedly because of the effect of mechanical agitation and is similar to the separation of fibrin of blood when beaten. Milk for custards is often heated before mixing with the egg and sugar. Forewarming of the milk may tend to prevent curdling of the milk, but the greatest advantage is probably in shortening the cooking period. Coagulation temperature of custards. The temperature at which a custard begins to coagulate or thicken is higher than the temperature at which the egg alone coagulates. The exact point at which coagulation starts is more difficult to ascertain than in the egg white, since the coagulation must be determined from the thickening of the custard. But not much occurs below 80°C. at ordinary rates of heating nor below 78°C. at slower rates of heating. As the soft custard coagulates, a thick layer will cling to a spoon that is dipped into the custard. In cookery this is known as ''coat- ing a spoon" and is one method of estimating when the custard is sufficiently cooked. The temperature at which coagulation starts varies with the vary- ing proportion of ingredients of the custard and the rate of cooking. In class results, the coagulation of a custard made of 1 cup of milk, 2 table- spoons of sugar, and 1 egg has never been perceptible below 78°C.