Fruit for making preserves or Konfyt should be on the green side, and should be perfectly sound and free from all blemishes. Any bruised spots or defective portions may be cut out and the fruit used for jam or jelly. After fruit has been peeled drop into cold water made slightly acid or salt, which will prevent discoloration.
In making preserves, fruit will be found to retain its shape and colour better when done in small quantities and when cooked fairly rapidly. Soft, juicy fruits, however, should be dropped into thick boiling syrup and allowed to simmer gently until cooked through, but not long enough to break them. Watermelon and fig preserves require long, gentle cooking in the syrup after having been parboiled in water.
In the case of thin-skinned juicy fruits that are liable to break in long cooking, a method commonly used is to pour the boiling syrup over them for three successive days, allowing them to stand in the syrup. The syrup on the second and third mornings is poured off, re-heated, and poured over the fruit. This method, however, cannot absolutely be relied upon, as fruit is apt to ferment.
In preserving fruit, only the best quality sugar should be used. The addition of dried ginger root or cinnamon bark is agreeable, while a little lemon juice or tartaric or citric acid helps to counteract the tendency of crystallisation.
The best saucepans to use are porcelain-lined or enamelled ones - round enamelled basins will be found to be excellent for preserving purposes. For stirring use a wooden or enamel spoon.
After fruit has been filled into the jars, a round piece of white parchment paper dipped into brandy or alcohol is often placed on top in order to prevent any germs or moulds, which may have settled on top, from developing. Preserves should be filled into sterilised, dry jars (see Sterilisation), and stored in a cool, dry place.
Sometimes blue vitriol or copper sulphate is added to preserves to make the fruit retain its green colour. This practice is to be strongly discouraged, as blue vitriol is a deadly poison, and, although it may not prove injurious at the time of eating, the effect is bound to be harmful in time.