PRESERVATION.
As the supply of food is always subject to ireegu. larities, the preservation of the excess obtained at one time to meet the deficiency of another would soon engage the attention of mankind. At first this method would be simple and natural, and de rived from a very limited observation ; but, in the progress of society, the wants and occupations of mankind would lead them to invent means by which the more perishable alimentary substances of one season might be reserved for consumption at an other, or the superfluous productions of distant coun tries might be transported to others where they are more needed. The principles of this most important art have been no where better explained than in the 45th Number of the Edinburgh Review, by an emi nent vegetable physiologist. We have only to re gret that he did not fill up the plan with a sketch of which he has concluded the article.
In general, organic substances, as soon as they are deprived of life, begin to undergo certain chemical changes, more or less rapidly, and of different kinds according to their nature. Although the modes of change, especially in the first stages, are almost as numerous as the substances themselves, yet ulti mately they terminate in one or more of the princi pal kinds of fermentation described by chemists. To each of these, besides the presence of an orga nic substance capable of undergoing it, several con ditions are requisite, of which the principal are a certain temperature, a certain degree of moisture, and the access of air ; and it is by obviating or mo difying these conditions that we are enabled to pre vent or regulate the natural fermentation. The kind of fermentation which substances undergo de pends upon their composition, and it may be gene rally remarked, that •those which do not contain a considerable proportion of azote are incapable of the putrefactive fermentation, but pass through the vi nous, acetous, and destructive, successively. On the other hind, those which contain a large proportion of azote are capable only of the putrefactive and destructive ; but there are many substances contain ing a small proportion of azote, in which both kinds of fermentation are combined.
A great proportion of vegetables are used in a recent state, and, in this case, the sooner after they are gathered the better. Vegetables, in general, should be kept apart, for, if laid in contact, in a very short time they impart their peculiar flavours to each other. Leeks or celery will quickly spoil a whole basketful of cauliflower or the finer vegetables. An.. other general rule is, that they should not be kept in water, nor even washed or refreshed by sprinkling them with water, till they are to be used, as the flavour is thereby greatly injured ; but if, by having been cut or gathered some time, they have become flaccid, it is absolutely necessary to restore their crispness before cooking them, otherwise they will be tough and unpleasant. This is to be done, when the size of the vegetable admits of it, as cauliflower, salted, celery, &c. by cutting off a piece of the stalk and setting the fresh surface, thus exposed, in water, which will be absorbed ; in other cases the whole vegetable must be immersed in water.
Most vegetable substances being more or less succulent, their full proportion of fluids is neces sary for their retaining that state of crispness or plumpness which they have when growing. On being cut or gathered the exhalation from their surface continues, while, from the open vessels of the cut surface, there is often great exudation or eva poration, and thus their natural moisture is dimi nished, and the tender leaves become flaccid, and the thicker masses or roots lose their plumpness. This is not only less pleasant to the eye, but is a real injury to the nutritious powers of the vegetable ; for in this flaccid and shrivelled state its fibres are less easily divided in chewing, and the water which exists in vegetable substances, in the form of their respective natural juices, is directly nutritious. The first care in the' preservation of succulent vegetables, therefore, is to prevent them from losing their natu. ral moisture. In regard to the tender succulent ve getables this is not altogether possible ; because there is a constant exhalation from their surface, while the supply of moisture is cut off. The principle of pre serving them, then, is to retard and diminish the ex halatiou. This is most effectually done by protect ing them from the action of the sun's rays, from the air, and from heat. Even growing vegetables be come flaccid in a hot sun, because the exhalation is then greater than the supply ; and exposure to the sun is absolutely ruinous to all the more delicate vegetables. The operation of heat and air is slower but similar. Succulent vegetables should, therefore, be kept in a cool, shady, and damp, place. They should also be kept in a heap and not spread out, which greatly influences their shrivelling. But when accumulated in too large heaps for any length of time, they are injured in another way, by their heat ing, as it is called, which is the commencement, in them, of a chemical change, or fermentation, which altogether alters their nature. In many cases the chief business is to prevent evaporation. Potatoes, turnips, carrots, and similar roots, intended to be stored up, should never be cleaned from the earth adhering to them, because the little fibres, by which it is retained, are thus wounded, and the evaporating surface is in creased. They should also be wounded as little as pos sible, and the tops of turnips and carrots should be cut off close to, but above, the root. The next thing to be attended to is to protect them from the action of the air and of frost. This is done by laying them in heaps, burying them in sand, or in earth, immersing them in water, or covering them with straw or mats. The action of frost is most destructive, as, if it be considerable, the life of the vegetable is destroyed, and it speedily rots. A less degree of frost induces a singular but hurtful change upon the potatoe, by converting part of its starch, or mucilage, into sugar. The germination of seeds also convert their starch into sugar, as is exemplified in the malting of barley. But, even after this change has been induced, if the substance be thoroughly dried in a kiln or other wise, it will still remain a long time without decay.