THE ORCHARD.

New Zealand Mail, Issue 1156, 27 April 1894, Page 5

THE ORCHARD.

PRESERVATIVES FOR FRESH FRUITS. Dining the present fruit season there has been much discussion regarding the merits of preservatives. We have given some attention to the subject, and would submit the following remarks by Professor E. W. Hilgard, of the U S Experiment Station, being well worthy of attention : 1. The preservatives mu:st prevent all fermentation, moulding, or other fungus attacks. This, of course, means that the outside of the fruit, and the air or the liquid around it, shall be " sterilised " in some way compatible with the preservation of the form, at least, of the fruit or vegetable This, again, excludes any considerable heat* iug, such as is necessary in •' putting up " fruit fjr eating purposes. We are practically reduced to the use of antiseptics, acting at the ordinary temperature. Among these we have to choose between gases and liquids; but, as the manipulation of gases does not come within the condition of easy practicability in an ordinary housohold, we are further confined to the use of liquids only ; the more, as these help to prevent damage in transportation by removing the greater part of the weight of the individual fruits that would otherwise tend to deform them* Hence,

2 The preservative should be a liquid. This liquid, besides being an efficient antiseptic, should not exert any solvent or softening action upon the skin of the fruit. This condition excludes from the outset all alkaline solutions (such as, e.g., cyanide of potassium, silicate of soda, &c.) and all the stronger acids, including acetic acid or vinegar. 3. The antiseptic fluid should not extract or change the colour of the fruit. This is one of the most difficult conditions to fulfil, and yet one of the most essential. It excludes at once 80 excellent a preservative as alcohol and many others that would otherwise be available ; among others, common salt, which is available at most for green fruit.

i. The preservative fluid should neither cause the fruit to swell, so as to increase its size, and sometimes burst it; nor should it have the opposite effect of causing it to shrink. This implies that in the exchange that will unavoidly occur between the juice inside and the fluid outside, the two shall pass through the skin with about equal rapidity. According to well-known physical laws, this necessitates that the two liquids shall be approximately of the same density. Thus, if the fruit to be preserved were grapes containing a juice showing 25 per cent, by spindle, the fluid outside ought to be made of the same density. If not, the fruit will either shrink or swell, at least at first: in some cases the original bulk will ultimately be recovered; but usually, particularly in thick skinned fruits, the change is more or less permanent. Thus, in pickling ripe olives, the size of the fruit may be materially reduced, and their substance toughened when too soft, by the use of strong brine. The same is pre-eminently true of fruit preserved in alcohol or in strong syrup. Whatever, then, may be the kind of antiseptic employed, this condition of approximately equal densities of the fruit juice and preservative fluid must be fulfilled if the former is <o maintain its natural size, especially if the fruit be soft or thin-skinned.

The use of sugar to bring up the antiseptic solution to that of the fruit juice naturally suggests itself, and with some fi uits very good results may be obtained in that way. Still, Sugar itself being easily fermentable and liable to change tint when not very pure, it is preferable to use glycerine f which can now be obtained so cheaply as to render it available to all, and which is, for practical purposes, unchangeable when so used. According to actual trial, commercial " pure " glycerine will act very satisfactorily when used per cent, for per cent, by weight in place of sugar. To do this by liquid measure, use four-fifths per cent, of glycerine as equal to one per cent, of sugar. Like alcohol, however, glycerine exerts a slight solvent action upon many fruit colours, e.g., that of cherries, blackberries, &c. Common salt has the advantage of darkening all vegetable colours after a comparatively short time; and Glauber's salt, alum, and other commonly available salts exert a not inconsiderable solvent action upon colours, which renders their use inadvisable.

It is not always, of course, easy to

ascertain the density of the juice of fruits, but the housewife or farmer may rest content with the following approximations to the soluble matters of fruit juices for ripe fruits : Apples and pcara, about 12 por cent. Plums, prunes, apricots, aud peaches, about 10 per cent. Cherries, about 12 per cent. Mo t berries, about Bpercont. Currants 10 per cent. Grapes, in CalifoinH, 18 to 30 per cent; average 24 per cent. It is only in very tender-skinned fruit that a per cent, or two, more or less, will make a difference in the result. Of antiseptics, the following are the most available ;—Salicylic acid, boracic acid, sulphurous acid and its compound, bisulphite of soda (and of lime), and last, but not least, bichloride of mercury or corrosive sublimate. Salicylic acid, or its compound with Boda, both obtainable in commerce, is one of the best and most energetic antiseptics. Its use in spirituous fluids is but too well known; in watery solution it is not so much used on account of some difficulty in making it dissolve, particularly when the water is cold. An ounce of the acid dissolves in a little less than five gallons of water at the ordinary temperature; but when it is simply thrown on the water it may float there a long time, being very light, and many persons will think that it will not dissolve in that proportion. In hot or boiling water there is no difficulty, and the solution is made very easily by the addition of a little carbonate of soda (sal soda) even without heating. But when making use of the soda it is absolutely necessary to avoid an excess, as the uncombined soda exerts a very injurious influence upon the preservation of fruits. A solution of loz of salicylic acid to five gallons of water, to which as much glycerine has been added as corresponds to the density of the fruit juice (see above), constitutes a preservative fluid which has been used with very satisfactory results heretofore. Trouble has arisen from the use of too much soda in making the acid dissolve, as already stated, with patience or heating, the water . alone will dissolfe the acid, and soda need not be used at all. Boracic acid, while an excellent preservative so far as the mere prevention of decay or fermentation goes, is more liable than the salicylic to soften . the skin and alter colours of fruit, act.- , ing in that respect, in some cases, like alkaline well adapted to long conservation of samples in their natural aspect, but will do well for a few weeks with most fruits. Use the solution as strong as water will make it, which is about soz per gallon. (To be concluded next week)