This section is from the book "Elements Of The Theory And Practice Of Cookery", by Mary E. Williams. Also available from Amazon: Elements Of The Theory And Practice Of Cookery; A Textbook Of Domestic Science For Use In Schools.
Before the principles of sterilizing were understood, fruit was preserved by cooking it with its weight of sugar. Such "preserves" are rarely made now. But jams, jellies, fruit butters, and marmalades contain enough sugar to preserve them. It is well, however, to sterilize, or at least to dip into boiling water, the tumblers or jars which are to hold them, and they must be covered air-tight to protect them from mould. Sugar should be added hot in making either jam or jelly. Measure it into a pan and set it into the oven. Take care that it does not scorch.
Jam is made of fruit and sugar cooked together till thick. Any kind of fruit may be used. Fruit butter is similar to jam, but thinner and less sweet. For jam allow three-fourths of a pound of sugar to one pound of fruit; for fruit butter, one-half to three-quarters of a pound of sugar to one pound of fruit.
Pick over and wash berries. Put them, a cupful or so at a time, into a preserving kettle, mashing those in the kettle before adding more. Cook slowly, stirring, and adding a little water if necessary to prevent sticking. Stir in the hot sugar slowly. Cook until thick. Put into glasses or jars. When cold, cover with paraffin, and put on tin covers.
Paraffin for covering jelly or jam should be hot, not merely melted. Pour on a layer one-fourth of an inch deep. Examine after it has cooled. If the paraffin shows bubbles, add another layer.
Marmalade, as ordinarily made, is jam of jelly-like consistency.
The jellying substance in fruit-juice is pectin.1
1 Pectin appears in several forms (pectose, pectocellulose, pectic acid, and the like). Just which of these are present in raw juice, in cooked juice, Pectin will not jelly unless acid is present and to make a good jelly sugar is necessary. It is important that the sugar be proportioned rightly to the pectin. Too little sugar makes tough jelly. Too much makes soft jelly, or even syrup. No exact rule can be given for the amount of sugar, because the amount of pectin varies in different fruits, and in different lots of the same fruit. After a rain currants are likely to be more watery than usual, and so to contain a smaller percentage of pectin.
Prepare, in separate test-tubes or small dishes, one tablespoonful each of lemon-juice, orange-juice, juice squeezed from raw currants, juice cooked from currants, and any other fruit-juices, from either raw or cooked fruit. To each portion of juice add one tablespoon-ful of grain alcohol. Note which juices contain much pectin, which a little, and which none at all.
Melt a little jelly, and test for pectin with alcohol.
Cooking appears necessary to extract pectin thoroughly from fruit. This may be because much of it is in the cell-walls of the fruit, and particularly in the harder parts, such as skin and core. In lemons and other citrus fruits much of the pectin is contained in the white inner skin. Whole oranges and grapefruit are among the best fruits for making marmalade.
Pectin acts much like gelatin, but in composition resembles carbohydrates. What do you know of the jelly-making properties of starch? of gelatin? Pectin is found largely in the framework of fruits and vegetables. What is gelatin made from?
and in jelly has not been determined. The change from liquid to jelly involves taking up water but apparently no marked change in composition.
The utensils needed for jelly-making are a large enamelled kettle, one or two large bowls or enamelled pans, quart measure, silver spoon, wooden masher, two yards of firm cheese-cloth doubled to make a square, jelly tumblers, and paraffin. A clean strong stick is convenient to hang the cheese-cloth on while the juice drips. A jelly-bag and a wire frame can be bought.
The best fruits for jelly are currants, crab-apples, partially ripened grapes (especially wild grapes), and tart apples. Cranberries also jelly easily. Blackberries and quinces come next. In the South and Southwest logan-berries and loquats are much used. Apple-juice is often combined with other juice lacking in pectin or in acid.
Currants and partially ripened grapes usually require as much sugar as juice. Red raspberries, blackberries, and fruits such as sour apples, crab-apples, and cranberries, to which considerable water must be added, take about three-fourths as much sugar as juice.
The best time to add the sugar is about midway of the cooking of the juice; after about five minutes for currants, after ten or fifteen minutes for other fruits.
Wash and drain the currants. They need not be stemmed. Put them into the kettle, a pint or so at a time, and mash them as they are put in. If they seem very watery, add no water. Otherwise add about one cupful of water to 5 or 6 quarts of currants. Stir and mash them while they heat. When they are hot and the juice is flowing, wring the double square of cheesecloth out of hot water and lay it over a bowl or pan. Transfer the mass of fruit to it, tie the corners, and suspend it over a bowl or pan by a stick laid across the backs of two chairs, or the rungs of a stool upside down. Let it drip until most of the juice is out, for from 30 minutes to one hour. Measure the juice. Measure an equal quantity of sugar. Heat the juice in a kettle, the sugar in the oven. Boil the juice for five minutes, removing scum as it rises. Add sugar. Boil three to five minutes longer. Test by dropping a little on a cold plate.1 When the plate can be stood on edge without making the jelly run, remove from the fire, and dip, or better, pour into glasses. When the jelly has set firmly, cover with paraffin. (P. 304.)
Put the mass of currants back into the kettle, cover with water, and heat again to obtain more juice. Proceed with this juice as with the first lot. Before adding sugar to it, take out a little and test for pectin. If much is found, a third lot of juice may be extracted and made into jelly.
If preferred, the first juice may be allowed to drip several hours or overnight, the bowl removed, and a second lot of juice squeezed out. This juice will make a less clear jelly, which can be used for jelly-cake, etc.
Wash, stem, and wipe crab-apples, or tart apples. Cut into quarters. Do not core. Barely cover them with cold water. Cook till soft. Mash, and let drain in cheese-cloth. Measure three-fourths of a cup of sugar for each cup of juice. Proceed as with currant jelly, adding sugar when the juice has boiled about fifteen minutes.
1 Another test is the jellying, or breaking off of the hot mass as it falls from the spoon.