CANNING WITH TIN CANS
46. For canning food in some tin cans, it is necessary to have a soldering outfit for properly closing them. This consists of a capping steel, a tipping iron, solder in small strips and in powder form, a small can of sal ammoniac, and a bottle of flux, which is a fluid that makes solder stick to tin.
47. Prepare the food that is to be canned in tin cans in the same way as for canning in jars by the cold-pack method; likewise, pack the cans in the same way, but allow the liquid and fruit or vegetables to come to within only 1/4 inch of the top. Then proceed to close the cans. Apply the flux to the groove in the top of each can where the solder is to be melted, using for this purpose a small brush or a small stick having a piece of cloth wrapped around one end. Heat the capping steel, which should be thoroughly clean, until it is almost red hot, dip it quickly into a little of the flux, and then put it into a mixture consisting of equal parts of sal ammoniac and powdered solder until it is covered with bright solder. Put the cap on the can and apply the hot capping steel covered with the solder. Hold this device firmly, press it downwards, and turn it slowly as the solder melts and thus joins the cap to the can.
48. After the caps are soldered in place, the air inside the cans must be driven out through the small vent, or opening, usually in the center of the cap, and the cans made air-tight. Therefore, place the cans into boiling water to within 1/2 inch of the top and let them remain there for a few minutes. Usually, 3 minutes in boiling water is sufficient. Immediately after exhausting, as this process is called, apply a little of the flux as in capping, and, with the tipping iron well heated and a strip of solder, seal the hole in the caps. After this is done, test each can for leaks by submerging it in water. If bubbles arise, it is an indication that the cover is not tight and must be resoldered.
49. The next step consists in processing the cans of food. This may be done either in a water bath or in a pressure cooker. If the cans are to be processed in a water bath, keep them in the boiling water just as long as glass jars of food would be kept there. If a pressure cooker is to be used, keep the cans in it for 6 to 40 minutes, depending on the steam pressure employed, the ripeness of the food or the necessity for cooking it, and the size of the cans employed. For canning meat or fish, processing in a pressure cooker is the most successful, as the high temperature reached in it kills bacteria, which are difficult to destroy at the boiling point.
As soon as the cans of food are removed from the water bath or the pressure cooker, plunge them into cold water to stop the cooking and prevent the food from getting soft and mushy. Then label the cans, so that no mistake will be made as to their contents.
50. In another method, the tin cans may be closed without soldering the caps on. The caps used in this case are different from those which must be soldered. They are forced in place by a hand-pressure machine that may be attached to a table. Otherwise the procedure is the same as that just given.