This may seem to the general reader a more inviting topic than the conservation of force, of which we are frequently called to speak. To our lady readers—for we are well aware there are plenty of them—who look weekly over our columns to find something to help them in their housekeeping duties, we are sure the topic will be interesting, although it may appear a little out of season to them. But they will remember when we put them in mind of it, that the putting up and conserving of fruit has got to be a business of very large proportions throughout the civilized world ; and although the bulk of it is put up in the summer and autumn, it is eaten throughout the entire year. Nay, it may be eaten for several years after it is put up, provided proper pains are taken. It is quite possible that the advice we shall give, if followed, may save much loss in the value of fruit already put up, and stored for sale. " Forewarned is forearmed " and to wait until the very time when information is wanted before attempting to obtain it, is something like death-bed repentance—mostly too .late. We recently had something to say on the subject of confectionary, which has called forth considerable correspondence, asking for an extension of the subject so that it should embrace the I conserving of fruit. In complying with this request, we shall first call attention to the chemical composition of fruits. To intelligently conserve anything, we should know what it is we wish to conserve. In all organic substances, the chemical elements which are essential to their existence exist in a state of combination. Destructive distillation or destructive fermentation resolves these, either into their ultimate elements or transforms them ; ; into new compounds. Any of the different kinds of fermen-j tations is the partial or entire decomposition of the natural | combinations (proximate principles), and their recombination into other and distinct combinations, during which some portions of the proximate principles escape as gaseous products, I while oxygen is taken up from the atmosphere or from other ! sources. The first step toward the total breaking up and destruction of any organic compound is some kind of fermentation. It follows, therefore, that if fermentation be prevented, ! the keeping of any organic substance for any length of time is possible. The proximate principles of plants, including fruits, are divided into two classes, those which contain nitrogen and thoss which do not contain it. The most important proximate principles not containing-nitrogen are starch, gum, fructose or fruit sugar, glucose or grape sugar, pectose or vegetable jelly, cellulose or cellular tissue, lignine or wood substance found in the skins of fruits as well as their stems, and cane sugar, or the sugar in common use for confections and domestic purposes. The important nitrogenized substances found in plants, are vegetable albumen vegetable casein and gluten. This class of proximate principles owing to the feeble affinities of nitrogen are, under favorable circumstances, particularly liable to decompose. Starch is acted upon by acids, and converted into glucose (grape sugar). This takes place in the ripening of fruits, as is shown by their greater sweetness when ripe, and also in the mellowing of fruits after they are plucked, which is neither more nor less than partial decomposition. From this it may at once be concluded that fruits which have become mellow to any considerable extent, are more or less unfitted for conserves, as they are already partly decomposed. It does not follow, however, that they are unfitted for food after becoming mellow—as has been asserted by some—unless the mellowing-has proceeded too far. When merely mellowed so as to "become palatable, the partial decomposition is, in some respects, analogous to that produced by cooking, and renders the fruit more digestible and wholesome. This mellowing will take place in the process of conserving, and in the jais, also, sufficiently to render the fruit tender and palatable, unless the fruit be immature, which is an extreme, also, to be avoided. Gum, although included in the list of non-nitrogenized proximate principles, has but little to do with the subject. Fructose and glucose will be considered in connection with cane sugar. Pectose is an important substance in its relations to the conservation of fruits. It is the proximate principle which becomes jelly when the juices of fruits are boiled. It is insol uble in water, until its characters are changed by the acids contained in the fruits aided by heat, which converts it into pectine which is soluble. It contains the same elements as sugar, but in a very different proportion. By continued boiling it loses its glutinous consistency, an important point as will be seen further on. The so-called " candying" of conserved fruits consists partly in the crystallization of the sugar employed, and the formation of jelly on account of over-betting Cellulose is only important as it forms the walls of the cells which inclose the proximate principles, and also of its intimate association with the pectose above alluded to. Lignine (wood substance) forms a portion of the rinds or skins of fruits. It is insoluble in water and, as found in the rinds of fruits, has little effect upon their preservation except to protect the more unstable interior compounds from the action of atmospheric oxygen. But all fruits contain more or less air in their interior, which, in the process of conservation, ought to be expelled and replaced by the substance used as a conserving agent. To avoid a too protracted heating of fruits, which is frequently injurious, they should either be deprived of their skins or the latter should be punctured. The sugars are the most important substances in this class. The elements of the sugars and their proportions by weight in the different sugars, are as follows : CAKBCW. HYDROGEN. OXYGEN. I WATEIi. Cane Sugar................. 5 9 73 I 18 ~ Grape Htigar (rStieose)___ 72 12 96 18 Fruit Sogar (Fructose)__ 73 13 96 | 00 As water is composed of one part by weight of hydrogen and eight parts of oxygen, it will be seen that only three elements are found in the sugars, and that the variations in their proportions are very slight. The natural change which cane and grape sugars first undergo When incipient decomposition sets in, is combination with Water, they thus becoming transformed into grape sugar. Alcoholic fermentation then Bets in, followed by the acetic and destructive fermentation and total decay. It is unnecessary, for our present purpose, to follow out the two latter fermentations, as when the alcoholic fermentation takes place the fruit, considered as a conserve, is already spoiled. It is true that the fermentation may be arrested by boiling, but the latter process so greatly deterio rates the appearance and flavor of the fruit that it is not too much to call it spoiled. Albumen is particularly liable to decay, but as little of it occurs in the pulp of fruit, and that contained in the stems is coagulated by heat during the usual processes of conservation, it need not be considered here. The same is true of caseine and gluten, except the remark upon coagulation. Thus it will be seen that the chemistry of fruit conservation is chiefly confined to the non-nitrogenized substances contained in fruits. Beside the proximate principles above enumerated, there are over two hundred distinct acids of vegetable origin which are isolated by chemists. But few of them, however, exist in a free state, they being for the most part combined with alkalies or vegetable alkaloids to form salts. Malic acid, which exists in the apple and its kindred fruits, citric acid which is j found in lemo'ns and kindred fruits, tartaric acid found in grapes in the form of tartar or bitartrate of potassa, oxalic acid, the acid of the sorrel and rhubarb, or " pie-plant," etc., I may be mentioned. A minute description of them is unnecessary. They all contain the same elements as sugar.in different proportions, and their action upon starch is, as above described, to change it into grape sugar. Having thus reviewed the principal substances found in fruits, let us next trace some of their more important reactions when decomposition takes place. First,the starch becomes more or less converted,first into dextrine,and subsequently into grape sugar which,being soluble.dissolves in the juice ; thus the solid portions ot the fruit become liquid and it becomes mellow. Vinous oralcoholic fermentation supervenes and the grape sugar is decomposed, alcohol being formed and carbonic acid being 139 disengaged. The alcohol thus formed is changed to acetic acid, thus constituting what is called the acetous fermentation. Finally the destructive fermentation begins, which speedily breaks up all the compounds not yet unchanged, and total decay is the result. Conserving fruit is the prevention of these changes for a greater or less period, by the use of cane sugar. The mechanical structure of fruits has, however, much to do with conservation. If you peel an orange carefully and then dissect it, it will be found to be made up of divisions, each of which contains a seed or the rudiments of one. Each of these divisions is covered with a continuous skin of cellulose which, although it would not totally prevent the absorption of liquid sugar would greatly retard it. If one of these divisions be dissected, it will be found to contain numerous sub-cells of irregular form, having the same cellular tissue for a covering. It is at once obvious, therefore, that an entire oiange would need to be kept much longer in a mass of liquid sugar, in order to become saturated, than one separated into the single divisions above described ; and the latter would also be slower in saturation than slices of orange, in which large numbers of the cells would be severed. It follows that it is necessary to consider the structure of the first in order to consume it in the best manner. Three results are to be attained in the proper conservation j of fruits, viz.: They must look well; they must taste well;! they must keep well. I The latter result depends upon the removal of air from the cellular structure of the fruits, replacing it with, and. enveloping the fruit in liquid sugar; by which means, if properly done, further danger of fermentation by the action of the atmospheric oxygen is obviated for a considerable time; although if the air be excluded by mechanical means (self-sealing jars), the fruit may be preserved much longer than without. In the latter case a solution of sugar may be employed, instead of concentrated sugar. This is much the best plan, as by it the natural taste of the fruit may be preserved if other proper precautions are taken. The putting up of fruits in concentrated sugar is rapidly going out of use for most domestic fruits, and it is to be rejoiced at, for a more ill-looking, ill-tasting compound than many of the old-time conserves, would be hard to find. The first thing to be done, in successful conservation, is the selection of the fruit. From what we have already said of the constituents of fruits and their chemical changes, it will be seen that it should be ripe, but not mellow or stale, of good size and fair surface. The next thing is the sugar, which should be the best white lump sugar obtainable. It should be perfectly dry, and should be destitute of foreign odors. Frequently a musty smell may be detected in sugar. Sugars sometimes also acquire the smell of kerosene, etc., by being placed in the vicinity where the latter is kept. The fruit and sugar being selected, the nature of the fruit should be well considered. Fruit looks very well when put up whole, but if in order to do so they require boiling until the pectose is changed to j elly, and the fruit is so cooked as to drive off its delicate flavors, you have paid dearly for the privilege of having your fruit whole. Beside, long boiling is sure to darken the color and thus damage the appearance. Apples should be quartered unless very small. Pears should be halved, unless quite small; the little Secklers may be put up whole. Peaches may be put up whole or halved, with the pits removed: the last is much better, as the prussic acid in the pits gives otherwise too strong a flavor to the fruit. All fruit having thick dense rinds should have the rind removed or punctured. Puncturing may be done by setting a number of very fine needles in a piece of pine wood which serves as i a handle. The use of an ordinary fork for the purpose is barbarous, as it makes the fruit appear as though it had had the smallpox and was just recovering. The fruit should be peeled or punctured only the shortest time possible before it is put in the sugar, otherwise it will become discolored, therefore the sugar should be first prepared. If, however, fruit when peeled or punctured be placed under cold water and kept until the sugar is ready its color will not change. If hermetically sealed jars are used only enough Sugar is needed to make the fruit palatable this should be put into a brass kettle with a little water,, and allowed to melt slowly, and then the heat should be gradually raised to nearly the boiling point. The fruit properly prepared is next put into the jars, from which it should not again emerge until wanted for the table. The amount of sugar proportioned to the fruit "by weight, established by previous experiment, should then, after being cooled, be divided as equally as possible between the jars, and the remaining space nearly filled with pure water. The jars should then be placed in a kettle containing cold water, pebbles being used to prevent contact with the bottom and consequent cracking of the jars, and the whole raised as quickly as possible to the boiling point and kept there about ten minutes. Too long boiling alters the taste and color of the fruit, and changes the pectose into jelly. It should be borne in mind that all the heating is intended to do is to expel the air, not cook the fruit. Whatever space is left in the jars should now be filled with hot water, and they should jbe immediately sealed. We have eaten fruit put up in this way that, after two full years' keeping, could scarcely be distinguished either in color or taste from that freshly prepared and placed by it on the same table. The old method of cooking fruit in sugar, pound for pound, is a relic of barbarism. The sugar needs to be boiled by itself in this process, else it will crystallize upon standing. Care is also necessary not to cook the fruit too long, else a gummy, sticky, dark-colored mass will be the result, as much inferior to fresh fruit as molasses is to nectar. "In making jellies the boiling is for the most part too protracted. The pectose, as we have seen, is the j elly principle of fruits, and it requires heat to cause it to farm a jelly, but too much heat causes it also to lose this quality. It is this that gives the granular consistence often seen in jellies which have been too long boiled. Fruit, after it is conserved, should be kept in a dry, cool, and dark place. All these requisites must be observed if you i desire perfection. The action of light discolors the fruit. Heat promotes fermentation. Dampness, strange as it may appear, also favors a sort of sub-fermentation, which greatly deteriorates quality. We can give no reason why outside dampness should affect fruit inclosed in hermetically sealed jars; but our own experience and that of others whom we have consulted on this point, warrant the assertion that it is a fact. Much, however, depends upon experience in this as well as other arts, but if the directions we have given be intelligently followed, in the light of the chemical principles involved, a guod degree of success is sure.
This article was originally published with the title "Conserving of Fruit" in Scientific American 20, 9, 138-139 (February 1869)