"Gelatine and its Uses"

Useful Recipes For Every Home

Compiled for the benefit of Warwickians and others by Anthony James Leahy

Printers: A Tomes Ltd, Leamington Spa circa 1930 (Centre Nelson's own  booklet) & Spennell Press Warwick (Right International Stores booklet) faded from original blue colour

Contents of both booklets essentially the same

Preface

      Since George Nelson, in 1837, invented the process by which Culinary and edible Gelatine is produced, many valuable discoveries have been made in relation to the dietic value of this wonderful product.

     Modern research has also provided a considerable fund of knowledge which should prove of inestimable benefit to present and future generation.

     An eminent American dietic expert says: "Gelatine has not yet found its place as a food. A better knowledge of it will greatly increase the use of it. It is not difficult to digest, and does not throw the nutritional balance out of order."

     It has long been the custom to feed Gelatine to sick persons, and the sick persons would be better off still if they "had twice as much gelatine as they get."

     "Gelatine is probably the greatest assimilative agent known, being able to save from distruction about half its weight of protein."

     "It is easily digested in the stomach and is instrumental in assisting to eliminate excess stomach acids."

     Gelatine is a great aid in the digestion and absorption of other foods especially in the case of Milk and Foods containing a high degree of fat or starch."

     The great importance of Gelatine in modern dietics is now being appreciated by the British Medical Profession.

     There are many reasons why this protein should be added to foodstuffs.

     Probably the most important is that when used in the form of jellies, or when applied to hot or cold soups, sweet confections, etc, it raises three preparations from the desserts to the nutritious food class.

     Gelatine has the property of improving the digestibility of difficult foods, and this is one of the reasons why it is added to Ice Cream, Invalid and Baby Milk preparations.

     When milk enters the stomach it frequently happens that gastric juices cause thick curds to separate. The fats of the milk are also carried down with the curds and make them tough and insoluble.

     These heavy curds are extremely difficult to digest, and in many cases they pass unchanged into the intestines.

     The addition of Gelatine to the food or milk will prevent this curdling, or at least will control it to such an extent that the curds are light and easy to assimilate.

     Doctors nowadays advocate the addition of a trace of pure Gelatine to Infants' Milk.

     When a small portions of Gelatine is added to the Infants' Milk, it has been discovered as a result of careful tests that fully 20 per cent. more of the milk is digested by the baby than in cases where no gelatine is used.

     Foods of the future will all contain Gelatine, as modern conditions of life demand a diet which is easy to digest and gives the highest results with a minimum waste.

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GELATINE.

GELATINE, which is a pure form of glue, is largely used for culinary purposes, and consequently in its preparation the raw materials require to be selected with great attention to purity, and the manufacture conducted with the most scrupulous care and cleanliness.

Gelatine is produced from white bones or hide pieces, that derivable from the former being mainly used in the stock for soups, etc., and as prepared gelatine, calves' foot jelly, and patent isinglass.

Bone Gelatine.

The preparation of bone gelatine depends on the separation of the organic from the mineral matter by an acid which dissolves the latter, leaving the ossein in the form of the original bone. The carefully picked and crushed bones may be degreased by a solvent, cleansed, and then subjected to the acid treatment; or, as carried out in some works, the fat is recovered in the after-process of boiling the ossein. In either case the crushed bones are conveyed to a series of vats 10 feet square by 3 feet deep, each of which is three parts filled and then covered with water containing 10 per cent, of hydrochloric acid. Phosphates of lime and magnesia and carbonate of lime mainly comprise the mineral constituents of the bone, and these salts are dissolved out by the action of the acid, leaving the gelatine-forming ossein intact. The steeping usually occupies about four days, the acidulated water being renewed once during this period. The bones now become soft, leathery, and semi-transparent, and in this condition are sufficiently prepared for washing to remove the acid. This is carried out by filling up each vat with fresh water, allowing it to soak through the bones for six or seven hours, and then draining. The washing is repeated until the wash-water shows no appreciable precipitate on the addition of a few drops of nitrate of silver solution. A slight turbidity may be due to the presence of combined chlorine in the fresh water.

When sufficiently washed, the soft bones are thoroughly bleached by immersion in a 1 percent, solution of sulphurous acid for three hours, and then conveyed to the vats A, fig. 20, to undergo digestion. The dissolving process is effected in the manner described under skin glue, care, however, being taken that the water covering the soft bones should never exceed a temperature of 85 C. when heated by the steam coils. Above this heat gelatinous solutions are very sensitive as regards colour.

During the digestion, the fat if the raw bones have not undergone a degreasing process rises to the surface and is carefully skimmed off from time to time, the skimmings being subsequently washed with hot water, before filling into casks.

A second digestion is necessary to practically exhaust the gelatinous matter, and the first and second runnings from the vats, having a density corresponding to 20 and 12 per cent, dry glue respectively, as indicated by the glue meter, then flow to the clarifiers and are treated with a small quantity of potash alum; from thence the liquors pass through the filters for concentration in the Yaryan evaporator to a jellying strength of 32 per cent, dry glue.

To obtain the colour necessary for a high-grade gelatine, the concentrated liquors undergo a further bleaching in the tanks EE, fig. 12, and are then run on to the glass slabs to a depth of half an inch for cake and quarter of an inch for leaf gelatine.

As a commercial product leaf gelatine is coloured with dye-stuffs to suit certain trade requirements. Carmine is a colour often employed for this purpose, and aniline colours are also used in the proportion of 1 ounce of colouring matter dissolved in a small quantity of glycerine to every 16 lbs. of liquid gelatine, the solution being strained through linen cloth and then mixed with the concentrated liquors before jellying. In the production of coloured leaf gelatine the liquors are not bleached after concentration. The method of manufacturing gelatine varies ; for instance, some French makers substitute phosphoric for hydrochloric acid in dissolving the mineral matter of the bone. For this purpose the carefully picked bones are dried at a temperature not exceeding 100 C. and then pulverised to a coarse powder in a mill. The powdered bones are then introduced into a circular vat provided with a stirrer, and the phosphoric acid, of 12 Tw. strength in the proportion of 1 cubic foot by measure to each 10 lbs. of raw material, is well stirred in the mass. The acid decomposes the carbonate of lime with evolution of carbonic acid, and converts the insoluble phosphates of lime and magnesia into soluble acid phosphates. The stirring is continued until the carbonic acid is wholly driven off; and on allowing the mixture to stand for a time, the crude gelatine falls as a sediment to the bottom. After the supernatant liquor has been syphoned off and precipitated with sulphuric acid to liberate the phosphoric acid for use again as a dissolving agent, the sediment is well washed with cold water and then treated with hot water of a temperature not exceeding 85 C., which dissolves the crude gelatine ; the liquor is afterwards clarified, bleached, and concentrated in the usual way.

'Osseine' is a French preparation from bones, and is brought into the market in a dry and concentrated state for the manufacture of gelatine. In using it the product is soaked in water for forty-eight hours, the water being renewed every twelve hours. When it is thoroughly swollen, the 'osseine' is well washed with water until the washings are absolutely clear, and yields a gelatine quite clear and without any smell.
The washed product is next bleached for one hour in a bath of sulphurous acid of 1 Tw. strength, and then finally dissolved at a temperature of 85 C. in a wooden vat fitted with a copper steam coil and provided with a double wooden bottom to distribute the heat. The gelatinous liquor is concentrated and jellied without clarification.

Animal charcoal is a powerful decolourising agent, and its use as a filtering medium has met with some success in obtaining a white gelatine from low-grade bone products, and also in improving the colour of the gelatine obtained as a secondary product in the manufacture of neat's-foot oil.

Skin Gelatine.

The preparation of gelatine from the parings and cuttings of hides varies but little from the process as described in the manufacture of skin glue. In some factories, instead of using lime only in steeping the hide pieces, a mixture of caustic soda and lime made into a milk with water is sprayed over the mass in the pits. The use of caustic soda facilitates the saponification of any fat present and the dissolving of the fleshy matter.

Before the digestion, which is effected at a temperature not exceeding 85 C., the hide pieces, on removal from the lime pits, are washed free of any alkalinity, and are then bleached by sulphurous acid to destroy any injurious colouring matter. To completely exhaust the gelatinous matter during digestion, three 'boilings' are generally required, the first and second runnings being treated for gelatine, while the third is simply filtered for size.

A very fine water-white leaf gelatine is produced by cutting the jelly into small pieces, washing well with cold water and re-melting at 80 C., then pouring the liquor on the 'glasses' to the depth required.

Seaweed Gelatine.

A product hardly distinguishable from gelatine, and used for many purposes in the arts similarly to that body, is known as seaweed gelatine, and is produced from a genus of weed to which the name of Laminaria is given. When macerated with water, about 33 per cent, of the weight of the air-dried weed is removed. The residue, when digested with carbonate of sodium, is partly dissolved, forming a soluble compound of sodium alginate. On filtering, the filtrate is mixed with hydrochloric acid, which liberates the alginic acid. The acid is washed, bleached, and re-dissolved in alkali, and by concentration in a vacuum pan and then running on glass plates or porcelain slabs, the sodium alginate is obtained in the form of trans- parent flexible sheets like gelatine and having the same colour, but they are not gelatinous. These sheets can be rendered insoluble without altering their appearance by immersion in dilute hydrochloric acid; they can also be readily coloured like leaf gelatine.

In America a gelatine is made from seaweed, called by the native name of Tengusa. The weed is carefully dried and afterwards boiled so as to form a glue-like decoction, which is strained off and put into square boxes. When cool it forms a thick jelly, which can be easily divided into squares a foot in length. The manner in which the surplus water is removed is very ingenious. The jelly prisms are exposed in the open air during a cold night and allowed to freeze. During the day the sun melts the ice to water, which runs off, leaving behind what might be termed a skeleton of white horny substance, which is extremely light, and easily dissolved in hot water ; when cool, it again forms stiff jelly. This article can be applied to many purposes for culinary purposes, for making bonbons and jellies, for clarifying liquids, as a substitute for isinglass, for making moulds used by the plaster-of-Paris workers, for hardening the same material in short, as a substitute for all kinds of gelatines, over which it has the advantage of producing a
firmer jelly.

Comparison of French and British Gelatines. The ash and water absorptive-power are indicative of the value of a gelatine, and in the following table a comparison is made of gelatines of French and British manufacture.

The Behaviour of Gelatine with certain Salts

Gelatine is unaffected when in contact with solutions of lead, tin, nickel, cobalt, manganese, aluminium, magnesium, and other metallic salts. With a solution of chloride of barium it is completely dissolved. It is also, although to a smaller degree, soluble in chloride of strontium. Other chlorides, such as those of potassium, sodium, and calcium, do not act in the same way, nor do their iodides or bromides. With a solution containing 15 per cent, chloride of barium, the solubility is so great that sufficient gelatine may be dissolved to render the solution syrupy in consistence. The liquid keeps well, and does not decompose under the action of air.

Allowed to evaporate spontaneously, it leaves behind a solid white substance which, when examined under the microscope, shows itself to be composed of an amorphous mass of filaments mixed with fine crystals of chloride of barium, but it does not appear that any combination has taken place. This solid substance dissolves in water completely. When exposed to light, gelatine is rendered insoluble in the presence of bichromate of potassium. Gelatine is precipitated from its solution by chloride of iron both in the light and in the dark.

SIZE AND ISINGLASS.

Size. As a cheap and easily workable agglutinant, size finds a ready use with calico-printers, painters, decorators, and in the carpet, straw-hat box, wallpaper and other trades. Size is undried glue, and exists as a tremulous jelly, possessing all the adhesive properties of the latter, but in a much less concentrated form.

In a sense, size is a bye-product in the manufacture of glue and gelatine, for the third liquors in the exhaustion of the raw material only are used for this purpose, and these, if converted into either of the above agglutinants, would yield an inferior product ; consequently it pays the manufacturer better to gelatinise it and to sell it in this form without drying. In small works exclusively making bone size the manufacturer with no benzene or glue plant at his disposal simply washes the rough bones in a revolving drum, and after crushing in a mill, feeds the broken pieces into an elevator, which lifts and discharges them into one or more digesters heated by ' live ' steam. When the bones are sufficiently acted on, the steam is turned off, and the grease and gelatinous liquor are blown through the outlet pipe to an overhead tank. After separating the fat, which is subsequently well washed with hot water to remove the impurities, the gelatinous liquor is filtered to separate any suspended matter, and then evaporated in a wooden vat fitted with a steam coil to the density required.

During the evaporation a moderate charge of sulphurous acid solution is sometimes added to improve the colour. Size is brought into the market as (1) common size; (2) medium size; (3) best size. The first contains 25 per cent, glue and 75 per cent, water; the second, 30 per cent, glue and 70 per cent, water ; and the third, 38 per cent, glue and 62 per cent, water. For exportation a stronger size is made in three grades, No. 1 containing 40'5 per cent, glue, No. 2 44.5 per cent., and No. 3 49 per cent., the liquors being evaporated to these densities before jellying.

Glue or gelatine in a dried state is a very stable body, but in the form of a jelly it soon ferments, becoming sour and mouldy, unless some preservative agent is used to prevent decomposition. For this purpose sulphate of zinc is principally used; boracic acid, and also a preparation known by the name of 'Salinfer,' have been used with good effect. These preservatives are added to the liquors before running into the casks to set.

In sorting the cakes of glue before packing, a number are always found unsuitable, owing to their having become twisted during the shrinkage in drying, or not equal to the standard as regards colour. These defects, while not lowering to any appreciable extent the value of the cakes as an agglutinant, yet affect their selling power. They now find a ready sale in a powdered condition as ' Concentrated Size ' or 'Glue Powder,' the cakes being ground, sifted, and graded by suitable machinery.

Isinglass.

The purest form of commercial gelatine is isinglass. This valuable product is obtained from the swimming bladder or sound of various species of fish, of which the sturgeon yields the finest quality. Isinglass is brought into commerce under the name of pipe, lump, honeycomb, purse, leaf, and other designations, and these different kinds are due to the method of preparing the bladder. For instance, pipe, purse, and lump isinglass consists of the sound desiccated, but unopened; while in the leaf and honeycomb kinds the bladder is cut open and then dried unfolded. When the cut bladder is folded and dried, the product is known as book isinglass, while in the ribbon isinglass it is rolled out. From Russia is obtained the finest quality of isinglass in the form of leaf, book, and long and short staple, the four varieties principally coming from Astrakhan and Taganrog. In preparing Russian isinglass, the swimming bladder is first cleansed of the mucus and blood stains by immersion in hot water, then cut open longitudinally and exposed to the air with the inner delicate silvery membrane upwards. When dried this fine membrane is removed by beating and rubbing, and the swimming bladder is made into the different forms by twisting or folding.

Brazilian isinglass is imported from Para and Maranham in the form of pipe, lump, and honeycomb. Pipe Brazilian isinglass is prepared by drying the swimming bladder unopened. When dry, each bladder is from 10 to 12 inches long and 2 to 2J inches broad, weighing about 5 ounces. Lump Brazilian isinglass consists of two swimming bladders placed side by side, considerably separated at one end, but communicating with each other at the other extremity. An average-sized lump will weigh about 6J ounces. Honeycomb Brazilian isinglass is the lump variety split open. The latter is sometimes softened and rolled out into thin strips, and is then known as ribbon isinglass. Brazilian, and also the isinglass imported from Hudson's Bay, Penang, India, etc., is the product of different species of fish, and is darker in colour and less soluble than the Russian variety. As received in this country, isinglass is a hard and tough substance, and for many purposes it requires to be cut into fine shreds to facilitate its solution.
According to Watson Smith, there seem to be only six isinglass cutters in England, all being domiciled in London. The crude isinglass is first sorted, soaked in water until it becomes a little pliable, and then trimmed. Sometimes it is just pressed by hand on a board with a rounded surface ; at others it is run once between strong rollers to flatten it a little and make the dark and dirty spots accessible to the knife, the top of the roller being used to bend the pieces on.

The cuttings are sold separately as an inferior grade. The next process is that of rolling. Very hard steel rollers, powerfully and accurately adjusted, are used. They are capable of exerting a pressure of 100 tons. Two are employed, the first to bring the isinglass to a uniform thick- ness, and the smaller one, kept cool by a current of water, to reduce the isinglass to a little more than the thickness of writing paper. It is very curious to see the thick, tough pieces gradually spreading out under the rollers and folded and rolled like puff pastry, till the separate pieces so unite themselves that no joint can be seen, and the mass is reduced, under the coarse rollers, to what looks like semi-transparent millboard. From the finer rollers it comes in a beautifully transparent ribbon, many yards to the pound, 'shot' like watered silk, in parallel lines about an inch broad. It is now hung up to dry in a separate room, the drying being an operation of considerable nicety. When sufficiently dried, it is stored till wanted for cutting, or is sold as ribbon isinglass to those who prefer this form.

The machines for cutting are well and accurately made, and are so adjusted that they slice pieces off a sheet of paper without bending it in the least. For the fine 'cut' isinglass, these machines are run at a great speed, 2000 to 2500 revolutions, making 10,000 to 12,000 cuts in a minute. It takes an hour to cut 5 lbs., so that every pound would contain 100,000 to 125,000 separate fibres, if none of them were broken. Isinglass is used in but few industries. The largest quantity is used by brewers and wine merchants for clarifying purposes. This property is extraordinary, for gelatine, which is chemically the same thing, does not possess it. One theory is that the tenacious mucilage shaken with the liquid gradually settles to the bottom, entangling all floating particles as it sinks. Another suggestion is that a very delicate fibrous network remains after the isinglass is dissolved, and entangles the particles in the way that the mucilage is supposed to act. Many varieties, generally the lower brands, are used for this purpose. Some brewers use it in the natural state, others prefer it manufactured into a fine or wide strip, which dissolves quicker and suffers no waste. At present Penang is the favourite kind. Russian long staple isinglass is used only by the Worcestershire farmers for clarifying their cyder. In spite of its costliness, Scotch brewers prefer Russian leaf. For clarifying purposes the isinglass is 'cut' or dissolved in acid, sulphurous acid being used as the solvent, owing to its preservative nature. When reduced to the right consistency, a little of the solution is placed in each cask before sending it out for consumption. Sole skins are sometimes used as a substitute for isinglass. They are only to be had in winter, the supply is uncertain, and they have not the strength of the Penang varieties. Next to the brewers' demand comes that of the cook, who uses it for making jellies, thickening syrups, and stiffening jams. Russian takes the highest position, owing to its superior strength and nourishing properties. Isinglass being the purest natural form of gelatine, a very fine article has long been known in the market as ' patent isinglass/ which is a gelatine of high quality. It does not, however, possess the clarifying power of the natural article, but is equally used for culinary and confectionery purposes. Outside the demands of the brewer and cook, isinglass has but a limited use in the arts. In textile works isinglass is used along with gum to give lustre to ribbons and other silk articles, while as a substitute for glass it answers well for lamp shades. Isinglass is also used in preparing a substitute for Indian ink; for this purpose three parts of isinglass are made into a size by dissolving them in six parts soft water. In another vessel, 1 part of Spanish liquorice is melted in 2 parts of soft water, over a fire, and then saturated with 1 part of ivory black. The two solutions are mixed together and stirred well. This mixture is evaporated to a thick syrup, and this is run into a leaden mould which has been slightly oiled, and allowed to set firm. The product is much of the same nature and applicable to the same purpose as Indian ink. As an agglutinant, isinglass is used in the form of diamond cement by dissolving two parts of it in four parts of spirit of wine, the solution on cooling yielding an opaque, milk-white, hard jelly. It also dissolves in strong acetic acid, forming a powerful cement, much used for repairing glass, pottery, and similar small objects.

The well-known court plaster is made by brushing a solution of isinglass, mingled with a small quantity of tincture of benzoin, over black sarsenet.

Isinglass is not suitable for photographic work, on account of its great solubility and inferior tenacity.

Extracts from: GLUE, GELATINE, AND THEIR ALLIED PRODUCTS 1907 - THOMAS LAMBERT, ANALYTICAL AND TECHNICAL CHEMIST.

 

Compiled for the benefit of Warwickians and Others by Anthony James Leahy

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