Glass jars should be tested before using: Partly fill the jar with water, adjust the rubber and cover, seal, invert the jar. Examine carefully for leakage.
RUBBER RINGS.—Soft, elastic rubbers should be chosen. It is poor economy to use old rubbers. Rubber after usage becomes hard and inelastic; it may cause imperfect sealing and hence decay of the fruit.
In certain processes of canning, it is necessary to subject the jars provided with rubber rings and covers to long periods of boiling or to the intense heat of a pressure or steam cooker. When such a method is followed it is especially necessary that rubber rings of good quality be used. To meet this requirement, the United States Department of Agriculture advises that rubber rings conform to the following:
1. Inside diameter of 2 1/4 inches (for the jar of standard size).
2. Width of ring or flange from 1/4 to 12/32 of an inch.
3. Thickness of 1/12 of an inch.
4. Tensile strength sufficient to "stretch considerably and return promptly to place without changing the inside diameter."
5. Firm enough so that no crease or break shows after it has been tightly folded.
SELECTION AND PREPARATION OF FRUIT FOR CANNING.—Select solid, and not over-ripe, fruit. It is better to have underripe than over-ripe fruit. Fresh fruits—if possible picked on the same day they are to be used—are desirable for canning.
Most fruits should be washed before using. Quinces should be rubbed with a coarse towel before they are washed. Berries and small fruits should be washed before they are hulled or stemmed. Most small fruits contain so much water that it is not necessary to add water for cooking. Hence such fruits should be drained thoroughly after washing. If there are any decayed or bruised spots on fruit, the damaged portion should be removed completely.