Pack the fruit as closely as possible in clean jars. Prepare a syrup and pour over the fruit, taking care to allow the syrup to come in contact with the fruit before touching the sides of the jar. Pill to within an inch of the top of the jar. Place the cap on but do not screw it down. Have ready a shallow pan containing about an inch of hot water or a sheet of asbestos cut to fit the sides of the oven. Place the jars in the pan or on the asbestos on the lower shelf in the oven. The oven must be cold or cool. Increase the temperature of the oven gradually until the fruit begins to bubble, then decrease the heat but keep it at the point where it will bubble but not violently. Too rapid cooking renders the fruit soft and mushy and causes a loss of the syrup due to overflowing.
When done remove from the oven with a dry clean cloth and place on a board or on a dry cloth. Have ready some of the boiled syrup and fill the jar to over-flowing. Allow any bubbles which may form in the can to escape by running a sterilized knife or fork down around the sides of the jar. Dip a new rubber band in boiling water and adjust to the jar, then screw down the cap and allow the fruit to cool where it will not be exposed to a draft.
Small fruits should be cooked only ten minutes from the time they begin to bubble. The larger fruits require from twenty to thirty minutes cooking. Most acid fruits may be put up in syrup, using equal quantities of sugar and water, though very acid fruits may require for palatability a syrup of two parts sugar to one of water. For the less acid fruits such as pears, blueberries, raspberries, peaches, etc., use one quart of sugar to two quarts of water.
Fruits may be put up without sugar, in which case boiling water is used to fill the can instead of the syrup.
For the small fruits allow a little more than a half pint of syrup to one quart of fruit. For the large fruits allow one pint of syrup to one quart of fruit. If less syrup to more fruit is desired the fruit should be cooked in the jars until tender, without the syrup, allowing ten minutes for small fruits and twenty to thirty minutes for the large fruits, from the time they begin to bubble. Then divide the contents of one jar of fruit between two other jars of equal size and fill with boiling syrup and seal in the usual manner.
When the Oven Method is used care must be taken to cook the fruit very slowly. Too hot an oven will break the iars.