The open-kettle method of canning is very simple and requires no equipment other than that to be found in every kitchen. It consists in thoroughly cooking the food that is to be canned, transferring it to containers, and sealing them immediately.
Not many utensils are required for the open-kettle canning method. For cooking the food, a large enamel or metal vessel other than tin or iron should be provided. It should be broad and shallow, rather than deep, especially for fruit, as this food retains its shape better if it is cooked in a layer that is not deep. The other utensils for canning fruits and vegetables by this method are practically the same as those already discussed—measuring utensils, a knife, large spoons, pans for sterilizing jars or cans, covers, rubbers, and jars or cans into which to put the food.
The first step in the open-kettle canning method consists in sterilizing the containers. To do this, first clean the jars, covers, and rubbers by washing them and then boiling them in clear water for 15 to 20 minutes.
Next, attention should be given to the food that is to be canned. Look it over carefully, cut out any decayed portions, and wash it thoroughly. Sometimes roots, leaves, stems, or seeds are removed before washing, and sometimes this is not done until after washing. At any rate, all dirt or foreign material must be washed from foods before they are ready for canning.
After preparing the food, it must be cooked. If fruit is being canned, put it into the required sirup, the making of which is explained later, and cook it until it is well softened, as if preparing it for immediate table use. If vegetables are being canned, cook them in the same way, but use salt and water instead of sirup. When the food is cooked, transfer it to the sterile jars and seal at once with the sterile rubbers and covers. Then invert each jar to permit the food to cool and to test for leaks.
The danger of not securing good results with the open-kettle method lies in the possibility of contaminating the contents before the jar is closed and sealed. In addition to having the jars, rubbers, and covers sterile, therefore, all spoons and other utensils used to handle the cooked food must be sterile. Likewise, the jars must be filled to the top and the covers put on and made as firm and tight as possible at once, so that as few bacteria as possible will enter. If screw-top cans are used, the tops should not be twisted or turned after cooling, as this may affect the sealing. If jars leak upon being turned upside down, the contents must be removed and reheated and the jar must be fitted with another cover. Then both jar and cover must be sterilized and the contents returned and sealed immediately.