This section is from the book "The White Ribbon Cook Book", by Kathryn Armstrong. Also available from Amazon: The White Ribbon Cook Book.
Fruit for preserving must be gathered in dry weather, and should be carefully selected, discarding all bruised fruit, and purchasing only that of the largest and finest quality. Use only the best white sugar. There is no economy in using common sugar, because it causes a greater amount of scum, which must of course be taken off. In making syrups the sugar must be pounded and dissolved in the syrup before setting on the fire; no syrups or jellies should be boiled too high. Fruits must not be put into a thick syrup at first. Fruits preserved whole or sliced may be boiled in a syrup made of two pounds of sugar to every pound of water, the quantity of syrup differing in some cases, but the general rule is one and a half the substance of fruit. The following has been found very good: To clarify six pounds of sugar, put into a preserving-pan, and pour into it five pints of cold spring water; in another pint beat lightly up the white of one small egg, but do not froth it very much; add it to the sugar, and give it a stir to mix it well with the whole. Set the pan over a gentle fire when the sugar is nearly dissolved, and let the scum rise without being disturbed; when the syrup has boiled five minutes take it from the fire, let it stand a couple of minutes, and then skim it very clean; let it boil again, then throw in half a cup of cold water, which will bring the remainder of the scum to the surface; skim it until it is perfectly clear, strain it through a thin cloth, and it will be ready for use, or for further boiling.
All unripe fruit must be rendered quite tender by gentle scalding, before it is put into syrup, or it will not imbibe the sugar; and the syrup must be thin when it is first added to it, and be thickened afterwards by frequent boiling, or with additional sugar; or the fruit will shrivel instead of becoming plump and clear. A pound of sugar boiled for ten minutes in one pint of water will make a very light syrup; but it will gradually thicken if rapidly boiled in an uncovered pan. Two pounds of sugar to the pint of water will become thick with a little more than half an hour's boiling, or with three or four separate boilings of eight or ten minutes each; if too much reduced it will candy instead of remaining liquid.
In making jams many cooks, after allowing the proper proportion of sugar, put the fruit into the preserving-pan without removing the stones or skins until after boiling, as the flavor is thought to be finer by adopting this method. Glass bottles are preferable to any other, as they allow inspection to detect incipient fermentation, which may be stayed by re-boiling. Copper or brass preserving-pans are the best kind to use, but they require a great deal of care to keep clean; the enameled are very nice ' and easily kept in order. Jams should be kept in a dry, cool place, and if properly made will only require a small round of writing-paper oiled, and laid on to fit, and tied down securely with a second paper brushed over with the white of egg to exclude the air.
To Preserve Fruit in Syrup
To every lb. of fruit allow 1 lb. of lump sugar, 1/2 tumbler of cold water. Boil the water and sugar together until it thickens slightly, which will take about 1/2 hour if the sugar be good. Take off the scum as it rises. Add the fruit and boil for 1/2 hour (rather longer if stone fruit), stirring very slightly, or the fruit will break. Take off the scum as it rises, but if both sugar and fruit be good there will be very little. Put into jars and tie over.
To Cover Preserves
Cut a round of thin paper the size of your jar, brush it over with white of egg, and place on the preserve egg downwards. See that it lies flat so as to keep out the air. Cut a round of white cooking-paper rather larger than your jar. Snip round the edge. Brush well over with white of egg, place on your jar, and stick down the edges round the jar with a dry cloth. Let your jam be cold before done, and let the paper on the top dry well before putting away.
N. B.-To keep well, fruit must be perfectly sound and dry when gathered.
 
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