Experimental cookery

5. Repeat 4 but pour berries into a large platter and let stand until sirup is the consistency desired. Seal in sterilized jar. 6. Repeat 4, but put berries in a sieve after stemming and pour boiling water over them. Put in kettle, add sugar, and proceed as under 4. 7. Make a sirup of 1 pound of sugar and 1 cup of water. When it is boiling add 1 pound of berries. Cook until the temperature of the sirup registers 103°C. Store according to directions under 1. C. To determine the effect of time of adding sugar in making preserves upon the texture of a firm fruit like Keifer pears. 1. Pare and core Keifer pears. Cut into quarters or eighths. To each pound of fruit add a pound of sugar and a cup of water. Cook until the sirup is the concentration desired. 2. Repeat 1, but first cook the pears until tender in water. Then add a pound of sugar for each pound of fruit and cook to the same concentration as under 1. Compare the consistency, texture, and flavor of the apples cooked in sirup with those cooked in water and then sweetened. Which is preferable for an apple that is to be served whole? For a puree? Would putting the cooked FRUITS AND VEGETABLES 151 apples through a sieve aid in obtaining a uniform texture for apple sauce? Are the apples used for the experiment a sweet or a sour variety? What is the concentration of sugar in a sirup that boils at 103°C. ? See Table 10 under sugar cookery. It is desirable for some preserves to have a greater concentration of sugar in the finished preserves. If 65 per cent of sugar is desired, to what temperature should the sirup be cooked? If a 70 per cent concentration is desired? What is the effect of longer cooking upon the flavor of strawberry preserves? Is it preferable to add the sugar directly to the berries or to make a sirup first? Why? Compare with the preserves from B in flavor, color, texture, and yield. In a fruit like Keifer pears, which contain considerable cellulose, what is the best method of making preserves? What is the effect upon the texture of adding the sugar directly to the fruit? Would you cook dried fruit in a sirup? Why? CHAPTER V JELLY The earliest work on jelly from a school laboratory is that of Gold- thwaite. Since that time many valuable contributions have been made deal- ing with jelly making. Probably the most extended recent investigations are those of Spencer, of Olsen, and of Tarr and his associates, Baker and Myers. They believe that the formation of jelly "depends almost entirely upon the application of the laws of chemistry, more especially the laws of physical chemistry." Jelly formation. Spencer offers a new theory for gelation of pectin jells. Stated briefly it is as follows. A pectin sol is stabilized by hj^dration and a negative charge of the pectin particles. The greatest stability comes in the neutral range as increasing either alkalinity or acidity decreases its stability. In jelly the role of the sugar is that of a precipitating agent: the more acid the solution, the less sugar required for the precipitation of the pectin. Salts may aid in precipitation or tend to prevent it, depending on whether they increase or decrease the stability of the pectin.