The products are in the hot jars now. The jars do not need to be full in order to keep. If you were canning by the "open-kettle" method, the air in the partly filled jar would not have been sterilized, and might contain the bacteria which cause the product to ferment or mold. But by the cold pack, the air in the can is sterilized while the product is being sterilized; and if the can is closed immediately after cooking, a single spoonful may be canned in a two-quart jar and the product will keep indefinitely.
Place Rubber and Cover on Jar. Fit the rubber. Use good rubbers and see that they lie flat and fit close up to the can. Put the covers in place.
Do Not Seal Glass Jars Tight. If using screw-top jars screw each cover down until it catches, then turn a quarter of a round back; or screw down with the thumb and little finger, not using force but stopping when the cover catches.
If using vacuum-seal jars put the cover on and the spring in place. The spring will give enough to allow the steam to escape.
If using glass-top jars, with the patent wire snap, put the cover in place, the wire over the top and the clamp up.
The cover on a glass jar must not be tight while processing, because the air will expand when heated, and if the cover is not loose enough to allow the steam to escape, the pressure may blow the rubber out or break the jar.
When canning in tin we cap and tip the cans at once. The tin will bulge out, but is strong enough to withstand the pressure, and when the contents cool the can will come back into shape.
The jars are now ready for the canner. Tomatoes sterilized under boiling water require twenty-two minutes; in condensed-steam cooker, twenty-two minutes; in water-seal, eighteen minutes; in steam-pressure, with five pounds, fifteen minutes, and in the pressure cooker, at ten or fifteen pounds, ten minutes.
If you use the homemade outfit or any water-bath outfit be sure the water is boiling when the jars of tomatoes are lowered into the canner. Time lost in bringing the contents to the point of sterilization softens the tomatoes and results in inferior goods. Use the ordinary good sense with which you have been endowed in handling the jars and you will have no breakage. At the end of the sterilizing period, remove the jars.
In taking canned goods from boiling hot water, care is needed to see that they are protected from drafts. If necessary close the windows and doors while lifting the jars out, for a sudden draft might break them.