Popular Science Monthly/Volume 23/September 1883/Ways of Preserving Food
By Dr. HERMANN KRÄTZER.
THE protein constituents of our animal and vegetable foods, such as albumen, etc., render them in a high degree sensitive to external influences and easily susceptible to decay. For this reason attention has for a considerable time been given to the search for methods of preserving them as long as possible unchanged. Formerly, this matter was left to the housekeeping department; but within the last eighteen or twenty years it has become an object of scientific investigation.
The most common methods of protecting meat, fish, vegetables, and fruits against destruction have been to preserve them in sugar, salt, or vinegar; and the processes of pickling, smoking, drying, pressing, and refrigeration, have been devised for this purpose. Extracts of the essential constituents have also been employed, and forms of compressed meat have been introduced. A number of other special methods of preservation will be described in this article.
A well-known process of securing meat, vegetables, etc., against decay is by canning, which consists in heating the substances so as to drive out the air, and sealing them up while still hot in air-tight vessels. For this purpose they are put into the cans, only a small hole being left in the top of the vessel and exposed to a salt-water bath, in which they are heated to a higher temperature than the boiling-point of pure water, when the can is closed. This method has the advantage of preserving all the nourishing qualities of the substances and their taste unimpaired. The use of glass and earthen ware jars instead of tin cans is familiar.
A method has been patented in England for preserving meat in gross. The beast is killed, and, after all the blood has run out, is at once skinned and disemboweled. It is then dipped entire into a mixture of 72 per cent alcohol and one per cent of carbolic acid, and after it has dried is laid in a concentrated alcoholic solution of sugar. It is then cut up and packed in casks which are afterward filled with melted fat.
By another English patented process the meat is soaked during from twenty-four to thirty-six hours in a solution of 150 grammes of boric acid, 300 grammes of borax, 155 grammes of common salt, and 53 grammes of saltpeter, which had been previously dissolved in two litres of water, after which it is packed in casks. A practicable method of preparing meat for long transportation is to expose it to a current of refrigerated air till it is stiffened, then sprinkle powdered borax upon it, and put it in a refrigerator-car.
Herr F. Wickerskeimer's process employs a solution of 36 grammes of potash, 15 grammes of common salt, and 6 grammes of alum, with three litres of water, which is heated to 122° and added to a second solution of 9 grammes of salicylic acid, 45 grammes of methyl alcohol, and 250 grammes of glycerine; and with this the whole animal is charged.
Kauffmann's method of preparation has been tried in household practice, with satisfaction. The top of a cask is removed carefully so that it can be tightly fitted in again, and a pan of sulphur is put in the bottom of the barrel and set fire to. The top, to which the meat has been hung, is then fitted in. By repeating the fumigation often enough, meat can be kept for a long time even in the summer, without ice, and without imbibing the odor or taste of the sulphur.
The exclusion of the air is sought in the canning processes. The real object is to exclude the germs of decay that are brought in with the air. The same purpose may be effected by filtering the air. To do this, a thickness of cotton between two pieces of linen may be put over the mouth of the jar. The vessel with its contents having been heated to expel the air within, the air that returns upon cooling deposits its germs upon the cotton in passing through it. The vessel may then be tightly closed with parchment-paper.
Among other methods of preserving foods are the familiar ones with sugar, salt, saltpeter, and vinegar. The first three substances act by withdrawing water from the conserves and leaving in place of it their own concentrated solutions, which are unfavorable to the development of germs. To obtain a perfect preservation, the solutions should be in a state of very great concentration and should surround the food-matter on every side. The sugar-process is expensive on account of the amount of sugar required to make it efficient. Dr. Bersch has suggested a way of cheapening it by adding salicylic acid to the sugar. His directions are to dissolve 100 grammes of sugar and three grammes of salicylic acid in hot water, and to pour the solution, after it has cooled to about 100°, over the fruit to be preserved. If the fruits are wholly covered with the solutions they can be kept in open vessels without changing; but it is best to seal the vessels with salicylic-acid paper (made by dipping common writing-paper into an alcoholic solution of the acid), so as to keep out the dust. Thus prepared, a ten per cent sugar-solution is strong enough for such fruits as cherries, apples, pears, etc., and an eighteen to twenty per cent one for the sweeter fruits. A difficulty in the application of this process arising out of the qualities of salicylic acid as to solubility may be obviated by previously dissolving the acid in glycerine. The old-fashioned way of packing meat in salt and saltpeter is bad, because it takes all the juices from the meats. It is preferable to prepare a brine by heating a kilogramme of salt, 160 grammes of white sugar, and 80 grammes of saltpeter in six litres of water over a gentle fire, and pour the mixture, after it has been cooled, over the meat.
Fruits, cucumbers, and meat, may be preserved for a long time with vinegar, by processes which are too well known to require a close description. Meat is not generally preserved by the direct action of vinegar, but by the vapors of acetic acid. For this purpose the meat is placed on a shelf in a cask, in the bottom of which concentrated vinegar has been poured. The escaping acetic vapors exercise a preservative influence which is effective for a considerable time. The processes of pickling and smoking are so well known that we speak particularly only of a rapid-smoking process, which consists in painting the meat some three or four times with a brush dipped in pyroligneous acid, after which it acquires the taste and properties of well-smoked meat.
The processes of direct drying, which have long been employed with fruits, have more recently been applied to vegetables. By late improvements they have been brought to a degree of perfection in which the freshness, taste, and tenderness of the fruits and greens, are well preserved. Potatoes are dried by Casseten, at Lubec, into a light, citron-yellow, gummy, transparent mass, which, when cooked with water and a little salt, regains the color and mealy consistency of the original tuber, and can not be distinguished by its taste from a freshly cooked potato.
Meat is dried, by the processes of Endemann and others, into a very nourishing food. By Endemann's method, the meat, cut into slices, is placed in a chamber heated to a temperature of about 140°, in which a current of air of the same temperature is kept constantly circulating. If the ventilation is sufficiently active the meat will be dry enough in three hours to be ground up in a mill. The powder, which has a faint smell of roast meat, is very good, and can be used in the preparation of soups and broths.
The meat-biscuit of Gail Borden is prepared by seething freshly killed beef with hot water till all the nourishing constituents are extracted. The solution of these constituents is then dried to the consistency of an extract, and this is mixed with flour into a dough which is made into cakes and baked in a moderately hot oven. According to Mr. Borden, five hundred grammes of the biscuit contain as much nutritive matter as two and a half kilogrammes of fresh meat. In a similar way, turnips, celery, spinach, and other vegetables, are dried and compressed in square cakes, which, enveloped in tin-foil, will keep fresh in the market for a very long time.
Other methods of preservation depend on the use of antiseptics. Besides carbolic and salicylic acids, borax, boric acid, boroglycerine, and xanthogenate of potash, may be used in preserving. Aqueous solutions of boric acid and borax are very effective preservatives, for many months, of meats, fish, vegetables, or fruits, which are immersed in them. Pulverized borax is also effective, whether by itself or mixed with pulverized alum and gypsum.
The substance called boroglycerine has recently attracted considerable attention. With it Professor Barff has prepared meat for preservation during long voyages, and has shipped experimental packages of beef across the Atlantic Ocean and back without their undergoing any change. Mr. Russell, President of the English Society of Arts, has also, independently of Professor Barff, found it excellent for the preservation of meat and milk. It promises to come into general use, for its application is without the slightest danger to the healthful or other qualities of the food, and it is very cheap. The "Deutschen Industrie Zeitung" gives the following directions for its preparation: Glycerine is heated to as high a temperature as it will bear without decomposition, and as much crystallized boric acid is added to it as it will dissolve. The usual proportion is 92 parts of glycerine to 62 parts of boric acid. The mixture is then heated to a temperature of about 400°, till after four or five hours the vapor of water ceases to pass from it. The resultant product, after cooling, is boroglycerine, in the form of a yellow, transparent mass, soluble in water and alcohol. It is applied to organic substances in solutions of one part to forty parts of water.
With xanthic acid, Professor Zöllner, of Vienna, has preserved beef and veal, poultry, pigeons, and over-ripe plums. Its operation is the more effective because it is volatile at ordinary temperatures, and a very small proportion of its vapor in the air of a chamber is efficient to prevent all decay.
A preservative salt, patented by a German manufacturer, consists of crystallized boric acid and phosphate of soda, to which a mixture of common salt and saltpeter is added.
We stop, without having yet exhausted the list of possible processes for preserving food. New ones are discovered from time to time, which may prove practically applicable for general use; and many are still in an experimental stage, not yet sufficiently tested or sufficiently perfected to justify recommending them to the public.—Translated for the Popular Science Monthly from, Die Natur.