80. The density of sirup is also affected by the amount and rapidity of evaporation that takes place in boiling, and these, in turn, depend on the amount of surface that is exposed. For instance, if a sirup is cooked in a large, flat kettle, the evaporation will be greater and more rapid than if it is cooked in a small, deep vessel. Atmospheric pressure affects the rapidity of evaporation, too. In a high altitude, evaporation takes place more slowly than at sea level, because the boiling point is lower. Thus, in the making of sirups for canning, the first point to be determined is whether the sirup desired should be light, medium, or heavy, and in its preparation the points mentioned must receive consideration.
81. For determining the density of sirup, a sirup gauge, or hydrometer, will be found useful. This device consists of a graduated glass tube attached to a bulb that is weighted with mercury. The graduations, or marks, on the tube, or top part, of the hydrometer serve to indicate the percentage of solid matter dissolved in a solution and register from to 50 degrees. To use such a gauge, partly fill a glass cylinder--an ordinary drinking glass will do--with the sirup and place the hydrometer in it. The greater the amount of solid matter dissolved in the sirup, the higher will be hydrometer float. Then read the number of degrees registered by observing the mark that is level with the surface of the sirup.
The number of degrees that the hydrometer should register for sirups of different densities--that is, for sirups consisting of different proportions of sugar and water--are given in Table I. This table, in addition, gives the uses that should be made of such sirups, and each one is numbered so that it may be referred to readily later in the recipes for canning fruits.
82. CLASSIFICATION OF FRUITS.--For the sake of convenience in canning, fruits, too, are here divided into groups. These groups, three in number, together with the fruits included in each, are:
1. Soft Fruits, which are subdivided into three kinds, namely, sweet, sour, and very sour. The sweet soft fruits include blackberries, blueberries or huckleberries, sweet cherries, elderberries, ripe gooseberries, mulberries, and black and red raspberries; the sour soft fruits, apricots, currants, grapes, peaches, and strawberries; and the very sour soft fruits, sour cherries, cranberries, green gooseberries, plums, and rhubarb.
2. Hard Fruits, which include apples, quinces, and pears.
3. Special Fruits, which include ripe figs, kumquats, loquats, nectarines, persimmons, and pineapples.
The advantage of this classification, as in the case of the vegetable classification, is that, as a rule, all fruits belonging to a group or a subdivision of a group may be canned in the same way and with sirup of practically the same density.
83. CANNING METHODS FOR FRUITS.--The canning of fruits may be done by the several methods previously discussed, but the Cold-pack and open-kettle methods seem to meet with most favor. On account of the sirup used in canning fruit and the acid in the fruit, the open-kettle method is usually fairly successful, whereas, in the canning of vegetables, with the exception of tomatoes, it is not so reliable. The housewife, by experiment, can determine which method will suit her needs best, but by no means should methods be mixed. If a certain method is decided on, it should be adhered to in every detail and carried through without any substitution. For all methods, as has been mentioned, the fruit should be selected when it is fresh and in good condition, as such fruit has less chance to spoil than fruit that is overripe or has decayed spots. After it is graded for size and condition, the fruit should be washed, stemmed, hulled, seeded, peeled, or halved, quartered, or sliced, depending on the kind. Then the work may be proceeded with according to the canning method that is to be followed.
84. If fruits are to be canned by the open-kettle method, certain precautions must be observed in order to insure success. The sterilization of the product cannot be perfect in this method no matter how carefully the canning is done; and this means that the sugar and the fruit acids must be greatly relied on to assist in preservation. Still, the jars, jar covers, jar rubbers, and any utensils used for filling the jars must be sterilized and kept in boiling water until the fruit is ready to be canned. Another thing to guard against is the discoloring of the fruit. Any fruit that is likely to become discolored after it is prepared for canning should be kept in salt water until it is ready to be cooked. A solution consisting of 1 teaspoonful of salt to each quart of water will answer for this purpose.