This section is from the book "Everywoman's Canning Book", by Mary B. Hughes. Also available from Amazon: Everywomans canning book; the A B C of safe home canning and preserving.
All fruits and berries may be canned successfully without the addition of sugar, simply by adding hot water instead of syrup. As sweetening must be added when the fruit or berries are served, there is no special advantage in omitting it, unless sugar is scarce or high in price. To fruit that is to be used for cooking purposes, such as pie filling, etc., add no sugar.
To can fruit, follow in general the canning instructions for vegetables, using the same equipment. Fruit that is to be preserved must be fresh, of fine flavor, and not overripe. When fruit reaches the point of perfect maturity, it begins to change in quality rapidly, and deteriorates.
Use a silver knife for paring fruit, and drop at once into slightly salted cold water, to prevent discoloration. Use two tablespoons of salt to a gallon of fresh cold water. Pack the fruit into clean jars, add syrup or simply hot water. Adjust rubber, cover, and seal lightly. Process the length of time given in the time table.
For home canning, a syrup gauge is not necessary to get the right proportion of sugar for fruit. Whether the syrup used is thick or thin is a matter of individual preference, and is not essential to the keeping of the fruits if they are properly processed. The addition of a large amount of sugar spoils rather than improves the flavor. Just enough sugar should be added so that the flavor is brought out and not obscured; moreover, the fruit should be eaten to take the place of fresh fruit in the diet, and not as a sweet preserve.
In judging the amount of syrup to make, it is important to know that large fruits, such as peaches, pears, etc., require just about twice as much syrup to fill the jar as the smaller fruits, owing to the larger spaces between. Well-packed raspberries, blackberries, or strawberries should take but little syrup.
Syrup will keep several days, and it is well to make it a day or two in advance of the actual canning, thereby greatly reducing that day's labor.
The simplest method in making syrups is to have one formula, which is given below. This may be made into a thin, medium, or thick syrup by boiling.
Put three quarts of sugar and two quarts of water in a preserve kettle, stir until the sugar is dissolved, and bring to the boiling point.
For a thin syrup, boil one minute. This syrup is used for sweet cherries, pears, or other fruits when very little sugar is desired.
For a medium thin syrup, boil the water and sugar five minutes. This is used for raspberries, strawberries, blackberries, blueberries, etc.
For a medium thick syrup, boil the water and sugar ten minutes. This syrup is used for acid fruits, like gooseberries, plums, rhubarb, currants, pineapple, etc.
For a thick syrup, boil the water and sugar until it will drop from the side of the spoon in drops. This should be used only for preserves.