Experimental cookery

and not at this temperature except when the rate of cooking is very slow. Occa- sionally a custard is heated slowly enough so that the best serving con- sistency occurs at 80°, provided the eggs are fresh so that the reaction has not become quite alkaline. It is possible to heat a cup of custard mixture in a double boiler from room temperature to the curdling point in less than 3 minutes. With this rapid rate of heating the custard is too thin to serve at 85° or even at 87° to 89°, and generally curdles about 89°, often after the temperature has remained stationary at 89° for a time. It may reach 91° or 92° and then drop back to about 89°, the curdling occurring before a serving consistency is attained. When the custard is cooked more slowly, and particularly if the heat- ing is slow after 75°C. is reached, thickening is quite perceptible at 80°, it has a consistency for serving from 80° to 84° ; that cooked more slowly being thicker at the lower temperature. A slower rate of cooking is pref- erable to the rapid one. With the slower rate of cooking the thickening is evident for considerable time before the curdling point is reached. With the rapid cooking, the custard requires very close watching and rapid work to remove it from the heat before the curdling temperature is reached. Curdling may occur at 84° if the temperature is raised very slowly, but in ordinary cooking it is more likely to occur between 85° and 87°C. Coagulation and particularly curdling in custards is accompanied by absorption of heat. In the custards heated slowly the temperature is usu- ally stationary for a considerable period before curdling occurs. In the rapidly heated custards the temperature often reaches 90° to 92° and then drops as curdling occurs. The temperatures given in the following discussion are for custards CUSTARD PIE 345 requiring 12 to 20 minutes from the time cooking is started to reach the curdling point. Concentration of egg and coagulation. If the proportion of egg in the custard is increased, thus increasing the concentration of the protein, coagulation starts at a slightly lower temperature, a firmer custard being obtained at a definite temperature as the proportion of egg is increased. Sugar. If the proportion of sugar to 1 egg and a cup of milk is increased, the coagulation temperature is elevated and coagulation begins above 80° C. The elevation of coagulation temperature is proportional to the amount of sugar added. If the custard is saturated w^ith sugar, coagulation does not occur at boiling temperature. Yolks. If two yolks are substituted for 1 whole egg the coagulation temperature is higher than for the whole egg. Whites. If two whites are substituted for the one whole egg the coagu- lation temperature is lower than for a custard made of the whole egg. With both the yolks and whites the coagulation temperature varies with the pro- portion of sugar used. The optimum temperature for cooking custards. Williams has reported that the curdling point for a custard made of 1 egg, 1 cup of milk, and 1 tablespoon of sugar is 83.5 °C. When the proportion of ingredients is varied the curdling point varies. If the proportion of egg is increased the curdling point is lowered ; increasing the sugar elevates the curdling point.