The best tomatoes for canning are those of moderate size, smooth and uniformly ripe.  When a tomato ripens unevenly or when it is misshapen, it is difficult to peel, and the percentage of waste is high.  Tomatoes should not be picked when they are green or partly ripe, for the flavor will not be so good as when they are allowed to remain upon the vines until fully ripe.  Care should be taken, however, not to allow them to become overripe before canning.

In no instance should a tomato with a rotten spot be canned, even though the spot is cut out, for the occasional spoiled jar resulting from this attempted saving will cost more than the partly spoiled tomatoes are worth.  If the housewife will can only uniformly ripe, sound tomatoes, saving the small, uneven but sound fruit for tomato puree, she will have a much better-looking pack and greater food value at the close of the season.  Yellow tomatoes may be canned in the same manner as are the more common red varieties, except that it is not necessary to remove the cores.

First of all, grade for ripeness, size and quality; this is to insure a high-grade product.  We could, of course, can different sizes and shades together, but uniform products are more pleasing to the eye and will sterilize much more evenly.  If the products are of the same ripeness and quality, the entire pack will receive the proper degree of cooking.

Wash the tomatoes.  Have ready a kettle of boiling water.  Put the tomatoes in a wire basket, or lay them on a piece of cheesecloth or a towel, twist the ends together to form a sack, and let this down into the kettle.  It is a good plan to slip a rubber band round the neck of this sack to hold the ends in place.  The ends should be long enough to stand up out of the water and so avoid danger of burning the fingers when removing the product.

Have the water boiling hard.  Lower the tomatoes into the boiling water.  This is called scalding the tomatoes.  We scald the tomatoes to loosen the skin.  If the tomatoes are very ripe, one minute scalding will be sufficient.  The average length of time for tomatoes, just perfect for canning, is one and a half minutes.  Do not leave the tomatoes in the hot water until the skins break, as this gives them a fuzzy appearance.

The scalding kettle always should be covered, to keep in all the heat possible.  Begin to time from the minute the product is immersed in the boiling water.  If you wait until the water comes back to a boil, you will scald the product too long and have mushy tomatoes.

Lift the tomatoes out of the hot water and plunge them immediately into cold water, or hold them under the cold-water faucet.  The cold-dip makes them easier to handle, separates the skin from the pulp, firms the texture, and coagulates the coloring matter so it stays near the surface, giving them a rich, red color.  Then the shock due to the sudden change from hot to cold and back to hot again seems to help kill the spores.  Do not let the product stand in the cold-dip.  The water becomes lukewarm, softens the product and allows bacteria to develop.