In canning fruit in tins, the same principle is followed as canning in glass jars, the fruit and syrup being prepared in exactly the same way. The only respect in which the process differs is that after the tins have been filled with fruit and syrup they are put into boiling water for 5 to 7 minutes, or according to the nature of the fruit, the lids having been soldered on previously, each lid containing a small vent hole in the centre, which is left unsoldered, through which the air can escape, and in the case of the tin with the lever lid being used, the lid is put on lightly. This is known as "exhausting," and is done in order to drive out the air - if omitted, the air left in the tin expands and so causes it to bulge. The tins are then removed from the boiling water, and the vent hole soldered up, or in the case of the lever lid tin, the lid is firmly and evenly knocked in, a little hammer being useful for that purpose. The tins are then replaced in the boiling water and sterilised according to the nature of the fruit.
Note. - The tin must be thoroughly washed before using for Syrups. Although they may appear perfectly clean, there may be acids or other foreign matter on the tin, which may cause decay. For the sake of convenience the syrups may be divided into three classes -
1. Thick Syrup: Made of equal parts of sugar and water.
2. Medium Syrup: Made of one part of sugar to two parts of water.
3. Thin Syrup: Made of one part of sugar to three parts of water.
To Prepare: To prepare the syrup simply pour boiling water on to the sugar, and stir until the sugar is dissolved, then strain through a double thickness butter muslin in order to strain out all impurities.