49. To insure the best results with the rising of bread mixtures, it is advisable, for the beginner at least, to use a thermometer for determining the temperature of air or water, as this instrument will save considerable time until experience in judging such matters has been gained. A Fahrenheit thermometer like that shown in Fig. 4 is the ideal kind for use in bread making. As an aid in this process, there are indicated in this illustration the temperature at which dough should be kept for rising and the temperature at which water should be kept outside the bowl to maintain a temperature of 75 to 90 degrees in the dough when the plan mentioned in Art. 48 for keeping dough at a uniform temperature is followed. In addition, the oven temperatures for baking bread and rolls, which are explained later, are also shown. The temperature of water can, however, be determined fairly accurately with the hands. If it feels very warm but does not burn the hand, it may be considered at about a temperature of 110 to 115 degrees.
In order to prevent the formation of a hard surface on the dough, the bowl in which it rises should be kept tightly covered. A further means of preventing this condition consists in oiling the surface of the dough; that is, brushing it lightly with melted fat. In case a crust does form, it should be well moistened with water or milk and allowed to soften completely before the next kneading is begun.
50. Time Required for Rising.--No definite rule can be given for the length of time required for dough to rise, for this depends entirely on the activity of the yeast. If the yeast is active, the dough will rise quickly; but if it is not of good quality or if it has been killed or retarded in its growth by improper handling, the dough will rise slowly. Usually, dough should be allowed to rise until it has doubled in bulk. A good way in which to determine when this takes place is to put a small piece of the dough in a glass, such as a measuring glass, a tumbler, or a jelly glass, and mark on this glass where the dough should come when it has increased to twice its size. This glass set beside the vessel containing the dough will show when it has risen sufficiently. This plan is illustrated in Figs. 5 and 6. Fig. 5 shows a glass half filled with dough and a bowl of bread dough ready to be placed where they will keep warm for the first rising; and Fig. 6 shows the same dough after it has doubled in bulk, as is evident from the fact that the glass is entirely full.