If you are using the vacuum-seal jars which have a composition attached to the lacquered tops, carefully examine this rubber composition to see that it is perfect. This composition should go entirely round the top and should not be cut or broken in any place. If it is the top must be discarded for a perfect one.
Of course with this type of jar no rubber rings are necessary, as the rubber composition on the lacquered top does the sealing.
It is a wise plan to go round the tops and over the inside of all new glass jars with a heavy and dull knife to scrape off any slivers of glass or bursted blisters that may be still clinging to the jars. Those on the tops cut through the rubber and cause leakage. Those in the jars may get into the product. I often find these splinters, particularly on new straight-sided jars.
It matters not what type of jar you use. Use what you have at hand, but if you are buying new jars consider the following things before making your selections: No metal, unless it is enameled or lacquered, should come in contact with the food. The jars should be of smooth, well-finished glass. The color of the jar does not affect the keeping qualities of the food. The top or part of the top that comes in contact with the contents should be all in one piece, so as not to offer a place for the accumulation of organisms and dirt. The jars which have nearly straight sides and a wide mouth or opening are easier to wash and facilitate better, quicker and easier packing of the product.
Wash the jars in soap and water. Rinse in boiling water. Some people temper new jars so they will stand the shock of hot water or hot sirup without breaking. If you wish to take this extra precaution put the jars in a dishpan or kettle of cold water after they have been washed in soapy water; bring the water slowly to a boil and let it boil fifteen minutes. After the jars are ready test the rubber rings. This may seem a useless precaution, but it is a necessary one, for there is no one detail in the business of canning that is more important. Even in the best boxes of rubbers there is occasionally a black sheep, and one black sheep may cause the loss of a jar.
Test each rubber before you use it by pressing it firmly between the thumbs and forefingers, stretching it very slightly. If it seems soft and spongy discard it. All rubbers fit for canning should be firm, elastic, and should endure a stretching pull without breaking. A good rubber ring will return promptly to place without changing the inside diameter.
A great many women are laboring under the wrong impression that color affects the quality of a ring. Some women insist on red, and others on white. Color is given to rings by adding coloring matter during the manufacturing process. The color of the ring is no index to its usefulness in home canning.
Use only fresh, sound strawberries or other berries. There is a little knack about preparing the strawberries that few housewives know. Hull the berries by twisting the berries off the hull, instead of pulling the hull from the berry as most women do. You will have a better-looking berry if you will be careful about this. Place the berries in a strainer and pour cold water over them to cleanse them.
HOW TO ADJUST THE COVERS
Never allow the berries or any fruit to stand in water, as the flavor and color are destroyed by water-soaking. Pack in glass jars, pressing the berries down tightly, but without crushing them. Put the rubber on the jar if you are using a jar requiring a rubber. Pour hot sirup over the berries. Put the top of the jar in place, but only partially tighten it.