2955—The Cooking, Potting, and Sealing of Jams

The time allowed for cooking any jam whatsoever can only be approximately decided, and it is a gross mistake to suppose the case otherwise, since the matter is wholly dependent upon the intensity of the fire, and the resulting speed of the evaporation of the vegetable moisture. Theoretically, a jam is all the better for having been cooked quickly, seeing that it may thus more easily preserve its colour and flavour.

For all that, unless great care and attention be exercised, a whole-fruit jam ought not to be made on a too violent fire, lest it burn. Conversely, when jellies are in question, wherein the juice alone of the fruit is treated, the fire should be as intense as possible; in order that the required degree of consistence, which marks the close of the operation, may be reached as speedily as possible.

The degree of consistence is the same for all jellies, and may be ascertained thus: when the steam given off by the preparation loses its density, and the boiling movement becomes perceptible, it may be concluded that evaporation has ceased, and that the real cooking-process, which is very rapid, has begun. At this stage frequently take the skimmer out of the saucepan.

The jam adhering to it falls off, at first very quickly; then, in a few minutes, it is seen to accumulate towards the centre of the skimmer and to fall therefrom slowly at lengthy intervals, in large drops.

This stage, which is indubitably indicative of the cooking being at an end, is called the “nappe” and is equivalent to the No. 2344, The Cooking of Sugar stage in the cooking of sugar; and, as soon as it is reached the jam should be taken off the fire. Allow it to cool for seven or eight minutes, and pour it into pots, which, if of glass, should be gradually heated, lest they crack.

The following day, set a round piece of white paper saturated with rectified glycerine, on each pot, and drop these pieces of paper directly upon the jam. Rectified glycerine will be found preferable by far to the commonly-used sugared brandy.

Then close the pots with a double sheet of paper, fastened on with string, and place them somewhere in the dry.