Edible fats and oils

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Underscores “_” before and after a word or phrase indicate italics in the original text. Equal signs “=” before and after a word or phrase indicate =bold= in the original text. Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. Deprecated spellings have been preserved. Typographical and punctuation errors have been silently corrected.

THEIR COMPOSITION, MANUFACTURE AND ANALYSIS

BY
W. H. SIMMONS, B. SC.(LOND.), F.C.S.

LECTURER ON SOAP MANUFACTURE AT THE BATTERSEA POLYTECHNIC AND JOINT AUTHOR OF THE “HANDBOOK OF SOAP MANUFACTURE” AND C. AINSWORTH MITCHELL, B.A.(OXON.), F.I.C.

JOINT AUTHOR OF “FIBRES USED IN TEXTILE AND ALLIED INDUSTRIES”

LONDON
SCOTT, GREENWOOD & SON
“THE OIL AND COLOUR TRADES JOURNAL” OFFICES
8 BROADWAY, LUDGATE, E.C.
1911

PREFACE

The importance of a due proportion of fat in the diet of man is insisted on by all physiologists, and the variety of forms in which fat enters into human food is very considerable. Formerly butter, lard, and dripping were the principal fats consumed as food, but the introduction of margarine by M. Mège-Mouries in 1872, followed, in more recent years, by the discovery of large quantities of new vegetable fats and oils, and of greatly improved processes for their preparation, purification, and refinement, has much augmented and cheapened the supply of fat for human consumption.

The popular prejudice against artificial butters has now been largely dissipated, and the edible fat and oil industry has become an important one.

The aim of the present volume is to describe, in a concise manner, the properties of the different edible fats and oils and their combinations, and to give an outline of the modern processes used in their preparation and purification.

Unfortunately the discoveries of science in this, as in other branches of technical chemistry, have led to the practice of a considerable amount of very skilful adulteration, and it is hoped that the somewhat lengthy chapter on the analysis of edible food products will be useful to those engaged in the industry in enabling such adulteration to be detected and successfully combated.

W. H. S.
C. A. M.
LONDON, April 1911.

CHAPTER I PAGE INTRODUCTION 1 Fat as Food—Physiological Considerations—Constitution of Fats and Oils.

CHAPTER II RAW MATERIALS USED IN THE MANUFACTURE OF EDIBLE FATS AND OILS 14

CHAPTER III REFINING, BLEACHING, AND DEODORISING FATS AND OILS 23 Physical Methods—Washing, freezing, filtration, treatment with charcoal and fuller’s earth, steaming. Chemical methods—Caustic soda, sodium carbonate and silicate, alkaline earths, ozone, hydrosulphites, sodium bisulphite, organic peroxides.

CHAPTER IV BUTTER 39

CHAPTER V LARD 56

CHAPTER VI MARGARINE AND OTHER BUTTER SUBSTITUTES 65 Margarine, Oleomargarine, or Artificial Butter—Invention and Development—Modern Processes and Formulæ—Vegetable Butter.

CHAPTER VII SALAD OILS 74

Salad Oils—Oils used for Culinary and Confectionery Purposes—Chocolate Fats.

CHAPTER VIII ANALYSIS OF RAW MATERIALS AND FINISHED PRODUCTS 89 General Methods of Analysis of Fats and Oils—Special Tests for Individual Oils—Analysis of Butter, Margarine, Lard, Cheese, Chocolate.

CHAPTER IX STATISTICS OF THE TRADE IN EDIBLE OILS 137

INDEX 145

EDIBLE FATS AND OILS

CHAPTER I

INTRODUCTION

Fat as Food—Physiological Considerations—Constitution of Fats and Oils.

The food of man may be divided broadly into two classes, nitrogenous, or flesh-forming, which is almost entirely of animal origin, and carbonaceous, or energy-producing, derived both from the animal and vegetable kingdoms. Besides nitrogen and carbon, many other elements, of course, such as phosphorus, calcium, iron, etc., normally enter into the composition of human food, but the nitrogen and carbon constitute the chief ingredients thereof, and are absolutely necessary to maintain the body in a healthy and efficient state.

There is an almost infinite variety of forms in which carbon may be taken into the stomach, but the vast majority of carbonaceous foods may be classified in two great chemical families: (1) the carbohydrates, comprising starch, sugar, and similar substances, which consist of carbon, hydrogen, and oxygen, the two latter in quantities having the same ratio as in water; and (2) the oils and fats, with which in the present volume it is proposed to deal.

Physiological Considerations.—The primary function of carbon-containing food is, by its combustion, to produce heat or other form of energy. The combustion of 1 gram of carbon to carbon dioxide produces 8080 calories; of 1 gram of hydrogen to water, 34,462 calories; whilst the presence of oxygen actually reduces the calorific value of the substance. Hence the higher the proportion of carbon, and lower the amount of oxygen, the greater will be the heat-producing power of a food; and since fats are much richer in carbon than starch or sugar, containing about 2½ times as much, they constitute the most concentrated form in which fuel can be supplied to the body. In the case of animal fats, carbon in the form of carbohydrate is converted into fat by the animal organism, and is thus rendered more suitable for the food of man; as although man in his internal economy, principally by means of his liver, is quite capable of himself transforming starchy matter into fat, in so doing he expends a certain amount of energy. Moreover, the human stomach is relatively smaller than that of an animal, and therefore a more highly concentrated form of carbon-containing food is desirable. Dripping is especially rich in carbon, containing over 10 per cent. more than does butter or suet, and it is regrettable that the use of dripping, formerly so popular among the working classes, has now become so largely a thing of the past.

The average relative proportions of fat and carbohydrate in the food of man vary with the climate, and are also governed to a considerable extent by their availability. Thus in very hot regions carbohydrates predominate, whilst in colder countries chiefly fat is consumed. The Eskimo takes almost all his carbon in the form of oil and fat, whereas the Indian or Chinese subsists mainly on carbohydrates. In this country the proportions recommended by physiologists, though varying slightly, are about 1 part of fat to 10 parts of carbohydrates, the amount of fat desirable being slightly higher in winter than in summer.

Besides its value as a heat or energy producer, the presence of a proportion of fat in human food is important in other ways, for the “food value” of any substance depends not only upon its composition, but also on its digestibility and palatability; and whilst fats are much more readily assimilated than carbohydrates, they also render more palatable, and assist in the digestion of, other articles of food.

Butter is the most easily digested of all fatty foods, and in cases where a fat diet is necessary, up to ¼ lb. of butter can be absorbed per diem. Margarine, which is usually made to approximate fairly closely to butter in composition, except in so far as the butter contains butyric and other volatile fatty acids, should be as digestible as butter, and is almost universally agreed to be so.

Yet another useful purpose served by a proportion of fatty food consists in facilitating the passage of masticated food to the stomach, and of the refuse matter through the bowel.

Constitution of Fats and Oils.—The difference between a fat and an oil is entirely dependent upon temperature, a fat becoming an oil when it is melted, and an oil a fat when solidified. The term oil is used for substances differing widely both in composition and properties, but all the fats and oils used for edible purposes are of the same general type of constitution, viz. esters or salts of glycerin with one or more fatty acids, which are termed “glycerides.” Their composition was first placed on a scientific basis by Chevreul, who in the early part of the last century showed that when a fat, such as tallow or lard, was converted into soap by the action of sodium or potassium hydroxide, the fat was decomposed into glycerin and fatty acids, the latter combining with the alkali to form the soap, while the glycerin, remaining free, was separated in the lyes. The three most commonly occurring glycerides are stearin and palmitin (of which tallow chiefly consists) and olein (the principal constituent of olive oil), and the action of sodium hydroxide on these may be represented by the following equations:—

CH₂OOC₁₈H₃₅ CH₂OH / / CHOOC₁₈H₃₅ + 3NaOH = 3NaOOC₁₈H₃₅ + CHOH \ \ CH₂OOC₁₈H₃₅ CH₂OH

(Stearin) (Sodium (Sodium (Glycerin) hydroxide) stearate) --------------------------------------------------------------------

CH₂OOC₁₆H₃₁ CH₂OH / / CHOOC₁₆H₃₁ + 3NaOH = 3NaOOC₁₆H₃₁ + CHOH \ \ CH₂OOC₁₆H₃₁ CH₂OH

(Palmitin) (Sodium (Sodium (Glycerin) hydroxide) palmitate) --------------------------------------------------------------------

CH₂OOC₁₈H₃₃ CH₂OH / / CHOOC₁₈H₃₃ + 3NaOH = 3NaOOC₁₈H₃₃ + CHOH \ \ CH₂OOC₁₈H₃₃ CH₂OH

(Olein) (Sodium (Sodium (Glycerin) hydroxide) oleate)

The conclusions of Chevreul as to the composition of fats were subsequently confirmed by Berthelot, who succeeded in producing the glycerides synthetically by heating the fatty acids with glycerin under pressure in sealed tubes. Heating together, for example, stearic acid and glycerin, he obtained stearin, according to the equation:—

3 C₁₈H₃₅O₂H + C₃H₅(OH)₃ = C₃H₅(C₁₈H₃₅O₂)₂

In view of the fact that glycerin contains three hydroxyl (OH) groups in which the H is displaceable by an acid radicle, it follows that compounds may be formed, in which only one, or two, or all three of the hydrogen atoms are replaced by an acid, compounds of the following types resulting; where R represents a fatty acid radicle.

Monoglyceride:—
CH₂OR CH₂OH
| |
(Alpha) CHOH and (Beta) CHOR
| |
CH₂OH CH₂OH

Diglyceride:—
CH₂OR CH₂OR
| |
(Alpha) CHOH and (Beta) CHOR
| |
CH₂OR CH₂OH

Triglyceride:—
CH₂OR
|
CHOR
|
CH₂OR

Intermediate products, corresponding to the above formulæ for the mono- and di-glycerides, were obtained by Berthelot in his syntheses, but in natural oils and fats glycerides are only met with in which all the hydrogen atoms in the hydroxyl groups are displaced by an acid.

Formerly it was believed that in nature the acid radicles combining with the same molecule of glycerin were all identical, but during the last few years a large number of so-called “mixed glycerides” have been discovered in various oils and fats, which may be represented by the above formula for the triglyceride, if the radicles denoted by R are assumed to be not all alike. Among these mixed glycerides may be mentioned oleodipalmitin, C₃H₅(OC₁₈H₃₃O)(OC₁₆H₃₁O)₂; stearodipalmitin, C₃H₅(OC₁₈H₃₅O)(OC₁₆H₃₁O)₂; oleopalmitostearin, C₃H₅(OC₁₈H₃₃O)(OC₁₆H₃₁O)(OC₁₈H₃₅O); and palmitodistearin, C₃H₅ (OC₁₆H₃₁O) (OC₁₈H₃₅O)₂ obtained by Hansen, and by Bömer from tallow; stearodipalmitin being also found in goose and turkey fat by Klimont and Meisels, and palmitodistearin in lard by Kreis and Hafner.

Oleodidaturin C₃H₅ (OC₁₈H₃₃O) (OC₁₇H₃₃O)₂ has been found in olive oil by Holde and Stange to the extent of one to two per cent., and it is probable that the butyric acid present in butter fat exists as a mixed glyceride, and not as butyrin; indeed, mixed glycerides are claimed to have been found in butter fat by Bell, and Blyth, and Harrison respectively.

The following are the chief pure triglycerides, together with their source, formulæ, and more important constants:—

LEGEND: (A) = Melting-Point °C. (B) = Refractive Index, at 60° C. (C) = Saponification Equivalent. ----------+----------------+------------------+------+-------+------ | | | | | Glyceride| Formula. |Chief Occurrence. | (A) | (B) | (C) | | | | | ----------+----------------+------------------+------+-------+------ Butyrin |C₃H₅(OC₄H₇O)₃ |Butter fat. |Liquid|1·42015| 100·7 | | |at -60| | Isovalerin|C₃H₅(OC₅H₉O)₃ |Porpoise, dolphin,| | | 114·7 | | and whale oils. | | | Caproin |C₃H₅(OC₆H₁₁O)₃ |Cocoanut and | -25 |1·42715| 128·7 | | palm-nut oils. | | | Caprylin |C₃H₅(OC₈H₁₅O)₃ |Cocoanut and | -8·3 |1·43316| 156·7 | | palm-nut oils. | | | Caprin |C₃H₅(OC₁₀H₁₉O)₃ |Cocoanut and | 31·1 |1·43697| 184·7 | | palm-nut oils. | | | Laurin |C₃H₅(OC₁₂H₂₃O)₃ |Cocoanut and | 45 |1·44039| 212·7 | | palm-nut oils. | | | Myristin |C₃H₅(OC₁₄H₂₇O)₃ |Nutmeg butter, | 56·5 |1·44285| 240·7 | | Butter fat. | | | Palmitin |C₃H₅(OC₁₆H₃₁O)₃ |Palm oil, lard. | 63-64| | 268·7 | | | | | Stearin |C₃H₅(OC₁₈H₃₅O)₃ |Tallow, lard, | 71·6 | | 296·7 | | cacao butter. | | | Olein |C₃H₅(OC₁₈H₃₃O)₃ |Olive and almond |Solid | | 294·7 | | oils. |at -6 | | Ricinolein|C₃H₅(OC₁₈H₃₃O₂)₃|Castor oil. | | | 310·7 ----------+----------------+------------------+------+-------+------

It will be observed that butyrin and olein are both liquid at ordinary temperatures, while tallow and palmitin have comparatively high melting points. Fats such as tallow or palm oil, therefore, in which the proportion of these latter is high, are firm and hard, the degree of hardness increasing with the percentage of these glycerides.

Butyrin (Tributyrin) may be obtained by heating together butyric acid and glycerin under pressure. According to Scheij its specific gravity is

20° 60°
d ———— = 1·0324, and d ———— = 0·9963.
4 4

It is almost insoluble in water, and has an intensely bitter taste.

Laurin (Trilaurin) may be produced by heating together lauric acid and glycerin. It is readily soluble in ether, but only slightly so in cold absolute alcohol, and crystallises in needles, melting at 45-46° C., and having, according to Scheij, the specific gravity

60°
d ———— = 0·8944.
4

Myristin (Trimyristin) may be isolated from nutmeg butter by fractional distillation in vacuo, or can be prepared by heating together myristic acid and glycerin. It crystallises in laminæ, which on heating first melt at 56°·5, but again solidify as the temperature is further raised, at 57-58°. The product then has a melting-point of 45-55°. Its boiling point in vacuo is 290-300°, and its density

60°
d ———— = 0·8848.
4

Palmitin (Tripalmitin) may be prepared artificially by heating together palmitic acid and glycerin, repeatedly boiling the product with alcohol, and allowing it to crystallise, when greasy scales are obtained, having a peculiar pearly appearance. The effect of heat on palmitin is somewhat curious, indicating the existence of distinct modifications. Thus when heated to 46° C. it liquefies, but again becomes solid on further raising the temperature, melting once more at 61°·7, and becoming cloudy, with separation of crystalline particles. Further increase of temperature to 63° C. renders the liquid clear, and this temperature is regarded as the true melting-point. After melting and re-solidifying, palmitin possesses no crystalline fracture.

Stearin (Tristearin) may be separated from tallow by dissolving it in ether and allowing it to crystallise, when small crystals separate, having a bright pearly lustre. Stearin when heated also shows the existence of two modifications. Thus, on raising the temperature to 55° C., stearin liquefies, but again becomes solid on further increasing the temperature until 71°·6 is reached, when it again melts. If this liquid is further heated to 76°, and then allowed to cool, solidification does not take place until the temperature has fallen to 55°, but if, after attaining 71°·6, it is immediately cooled, it will solidify at 70° C.

Olein (Triolein) is one of the most widely distributed natural glycerides, and may be prepared in an impure form from olive oil by separating the solid glycerides by cooling. After maintaining the oil at a low temperature for several days, and separating the liquid portion, the latter may be freed from traces of stearin and palmitin by solution in alcohol. Olein may also be produced artificially by heating together oleic acid and glycerin. It is an odourless, colourless, and tasteless oil, which may be distilled in vacuo, without decomposition, but which rapidly absorbs oxygen from the air, and becomes rancid.

As already stated, the natural glycerides of which edible fats and oils are composed, consist of combinations of glycerin with various fatty acids. These may be separated by saponifying the fat or oil with sodium or potassium hydroxide, dissolving the resulting soap in hot water, and adding sufficient dilute sulphuric acid to decompose the soap, when an oily layer gradually rises to the surface. This when melted by gentle heat and washed free from mineral acid, is soluble in alcohol and reddens blue litmus paper. It consists of the insoluble fatty acids of the fat, those soluble in water, such as acetic, propionic, butyric, caproic, caprylic, and capric, remaining for the most part dissolved in the aqueous portion underneath.

All the acids naturally present in fats and oils are mono-basic, i.e. contain only one carboxyl (COOH) group, but they may be arranged in five classes or homologous series, based on their chemical constitution, these series having the following general formulæ:—

I. Stearic Acid Series CₙH₂ₙ₊₁COOH.
II. Oleic Acid Series CₙH₂ₙ₋₁COOH.
III. Linolic Acid Series CₙH₂ₙ₋₃COOH.
IV. Linolenic Acid Series CₙH₂ₙ₋₅COOH.
V. Ricinoleic Acid Series CₙH₂ₙ₋₇COOH.

The more important members of these series, together with their formulæ, melting-points, and principal occurrence, are given in the following tables:—

I. Stearic Series

The acids of this series are all what is termed saturated compounds, i.e. they do not form addition compounds when brought in contact with bromine, iodine, or ozone. The two first are liquid at ordinary temperatures, distil unchanged under atmospheric pressure, and are miscible with water in all proportions. The next four are more or less soluble in water, and readily distil with steam, as does also lauric acid, though the latter is practically insoluble in cold water, and only dissolves very slightly in boiling water. These first seven acids are termed Volatile Fatty Acids, and on their volatility are based the Reichert process and its modifications and the Polenske method for the examination of butter fat for adulteration, vide pp. 111-114. The higher acids of the group are solid, and are completely insoluble in water. The whole series is readily soluble in warm alcohol, and undergoes no change when heated with solid caustic alkali.

II. Oleic Acid Series

These acids differ essentially from those of Series I. in being unsaturated, and combine directly with bromine, iodine, and ozone. The earlier members are readily reduced, by the action of sodium amalgam in alkaline solution, to the corresponding acids of Series I. Thus:—

C₄H₇COOH + H₂ = C₄H₉COOH
(Tiglic acid) (Hydrogen) (Valeric acid)

Unfortunately, however, from the candlemaker’s point of view, this reduction does not take place in the case of the higher acids of the series, and for the reduction of oleic acid to stearic acid other methods have to be adopted.

Acids of this group may also be converted into those of the Stearic Acid Series by heating them to 300° C. with solid potassium hydroxide, when hydrogen is also liberated, the reaction, with oleic acid, for example, being generally represented by the equation:—

C₁₈H₃₄O₂ + 2KOH = KC₂H₃O₂ + KC₁₆H₃₁O₂ + H₂

though since, as Edmed has shown, a considerable quantity of oxalic acid is also formed, the action must strictly be more complex than this indicates.

One of the most important properties of this group of acids, and one which is of great value in judging the purity of olive oil, is the elaidin reaction, which is based on the formation of isomeric acids of higher melting-point by these acids when treated with nitrous acid. Oleic acid, for example, when acted upon by nitrous acid, yields elaidic acid, melting at 45° C., and erucic acid gives brassic acid, melting at 60° C. A similar reaction also takes place with the neutral glycerides of these acids, olein being converted into elaidin, which melts at 32°.

The lead salts of the acids of this series are much more soluble in ether, and the lithium salts more soluble in alcohol, than those of the stearic series, upon both of which properties processes have been based for the separation of the solid from the liquid fatty acids.

III. Linolic Acid Series

These acids are also unsaturated, and readily combine with bromine, iodine, oxygen, or ozone. They do not give an elaidin reaction when treated with nitrous acid, and their lead salts are soluble in ether.

IV. Linolenic Acid Series

These acids are very similar in properties to those of the preceding series, but combine with six atoms of bromine or iodine, whereas the latter only combine with four atoms.

V. Ricinoleic Acid Series

This acid combines with two atoms of bromine or iodine, and when treated with nitrous acid is converted into the isomeric ricinelaidic acid, which melts at 52-53° C. It differs from most fatty acids in possessing optical activity, its specific rotation being

[a] = +6° 25′.
ᵈ

CHAPTER II

RAW MATERIALS USED IN THE MANUFACTURE OF EDIBLE FATS AND OILS

It is unnecessary to emphasise the absolute importance that all materials used for the preparation of edible fats and oils should be as fresh, odourless, and free from all impurities as possible. Albuminous matter, which facilitates the production of rancidity by enzymic action, must be carefully removed, and freedom from any appreciable quantity of free fatty acids is most essential. The absence of these latter should be sufficient to guarantee the absence of any rancidity, which though not due to, is generally accompanied by their production.

The methods of treatment by which freedom from odour and free fatty acids is secured, are fully described in the next chapter, and in the case of some of the materials, their actual preparation is dealt with in subsequent chapters. The following paragraphs give briefly the source, origin, and properties of the raw material employed in the industry.

=Tallow.=—Ordinary “dripping” is simply an impure form of tallow, but the name tallow is generally used to denote the adipose fat or “suet” from sheep and oxen, being distinguished in commerce as mutton or beef tallow. The latter is somewhat softer in consistency, and is therefore more usually employed in the manufacture of margarine, though mutton tallow is also occasionally used. “Premier jus” consists of the less firm constituents of tallow, separated from the harder stearin by partial melting and pressure, as described in Chapter VI. p. 69.

The chief sources of imported tallow are Australia, New Zealand, and North and South America. Some of the carefully picked tallow intended for margarine making is shipped to England “unrendered,” but in some cases the fat is not only rendered, but also converted into “premier jus” abroad before shipment. Large quantities of tallow are also produced in Great Britain, and much of the rough fat is carefully hand-picked, rendered separately, and the product sold for margarine making. The following figures have been obtained for some typical samples of tallow:—

+-----------------+----------------+-----------------+--------+ | | | Free Acidity | | | Tallows. | Saponification | (as Oleic Acid) | Titre, | | | Value. | per cent. | °C. | +-----------------+----------------+-----------------+--------+ | Mutton:— | | | | |Selected English | 197·6 | 1·45 | 47 | |Australian | 197·4 | 0·48 | 48·3 | |South American | 197·3 | 1·11 | 47 | |North American | 197·5 | 1·32 | 44 | | | | | | | Beef:— | | | | |Selected English | 197·5 | 2·40 | 44 | |Australian | 197·5 | 1·68 | 43·9 | |South American | 197·3 | 0·81 | 45 | |North American | 197·4 | 1·97 | 41·5 | +-----------------+----------------+-----------------+--------+

=Lard.=—This fat, obtained from the pig, is an important constituent of many butter substitutes, especially in the United States, whence most of that imported into this country is obtained. Its method of preparation and various qualities are fully described in Chapter V.

=Lard Oil=, obtained by subjecting the softer varieties of lard to hydraulic pressure at a moderate temperature, is also dealt with in Chapter V.

=Cocoanut Oil.=—This oil, after special refinement, is extensively used in margarine and chocolate-cream manufacture, and is also sold under various fancy names as vegetable butter. There are two principal commercial varieties, Cochin and Ceylon, the former obtained from Cochin (Malabar) or the Philippine Islands, and the latter from Ceylon. The following are analyses of typical samples:—

+--- -------+----------------+-------------+--------+------------+ | | | Acidity (as | | Refractive | | | Saponification | Oleic Acid) | Titre, | Index at | | | Value. | per cent. | °C. | 25 °C. | +-----------+----------------+-------------+--------+------------+ |Cochin oil | 255 | 1·5 | 23·5 | 1·4540 | |Ceylon oil | 258·2 | 5·47 | 23 | 1·4535 | +-----------+----------------+-------------+--------+------------+

=Maize Oil=, expressed from maize, and obtained chiefly from the United States, is occasionally used as an edible oil. A sample of refined maize oil has given the following figures on analysis:—

+---------+--------------+------+-----------+--------+----------+ | Specific| | |Acidity (as| |Refractive| | Gravity |Saponification|Iodine|Oleic Acid)| Titre, | Index at | |at 15° C.| Value. |Value.| per cent. | °C. | 20° C. | +---------+--------------+------+-----------+--------+----------+ | 0·9243 | 192 | 123 | 0·40 | 17·2 | 1·4766 | +---------+--------------+------+-----------+--------+----------+

=Cotton-Seed Oil.=—This is obtained by expression from the seeds of the various kinds of cotton tree, grown extensively in America, Egypt, and India. A considerable quantity of the oil is expressed from the seed in this country, principally at Hull. The refined oil is used in making artificial butter, and also for culinary purposes. The best cotton-seed oil, used for margarine manufacture, is sold under the name of “butter oil.” The following are typical figures for a refined cotton-seed oil:—

+---------+--------------+------+-----------+------+----------+ | Specific| | |Acidity (as| |Refractive| | Gravity |Saponification|Iodine|Oleic Acid)|Titre,| Index at | |at 15° C.| Value. |Value.| per cent. | °C. | 20° C. | +---------+--------------+------+-----------+------+----------+ | 0·9229 | 193 | 115 | 0·24 | 33·6 | 1·4721 | +---------+--------------+------+-----------+------+----------+

=Cotton-Seed Stearin.=—This is the solid residue remaining when the deposit obtained from ordinary refined cotton-seed oil by chilling is pressed. Its consistency is very similar to that of butter, and it is used in the preparation of some artificial butters. Its average properties are as follows:—

+----------------+--------+-----------------+--------+ | | | Acidity | | | Saponification | Iodine | (as Oleic Acid) | Titre, | | Value. | Value. | per cent. | °C. | +----------------+--------+-----------------+--------+ | 195 | 93 | 0·05 | 38 | +----------------+--------+-----------------+--------+

=Olive Oil.=—Edible olive oil is obtained by expression from the fruit of the olive tree, and is largely used as salad oil, in cookery, and for tinning sardines. Olive trees are grown extensively in nearly all the countries bordering on the Mediterranean Sea, also to a considerable extent in California. The oil obtained from their fruit varies a good deal in quality, according to its source, oils from Leghorn or Gallipoli being the most esteemed. The following figures were given by a typical high-class oil:—

+----------------+--------+-----------------+--------+------------+ | | | Acidity | | Refractive | | Saponification | Iodine | (as Oleic Acid) | Titre, | Index at | | Value. | Value. | per cent. | °C. | 20° C. | +----------------+--------+-----------------+--------+------------+ | 190 | 89 | 1·8 | 21 | 1·4704 | +----------------+--------+-----------------+--------+------------+

=Arachis Oil (Earth-Nut or Pea-Nut Oil).=—This oil, used occasionally in margarine to reduce its firmness, and a useful table oil, is obtained from the nuts of Arachis hypogæa, a herb cultivated largely in North America, India, and Western Africa. Most of the oil is expressed in Southern France, and its chief use appears to be as an adulterant or substitute for olive oil, which it closely resembles in many respects. The following figures were given by a sample of the refined oil:—

+---------+--------------+-------+-----------+------+----------+ | Specific| | |Acidity (as| |Refractive| | Gravity |Saponification| Iodine|Oleic Acid)|Titre,| Index at | |at 15° C.| Value. | Value.| per cent. | °C. | 20° C. | +---------+--------------+-------+-----------+------+----------+ | 0·9205 | 193 | 87 | 0·22 | 24 | 1·4712 | +---------+--------------+-------+-----------+------+----------+

=Sesame Oil.=—This oil is frequently employed in margarine manufacture, its use to the extent of 10 per cent. being compulsory in Germany and other countries, in order to simplify the detection of adulteration of butter with butter substitutes. It is largely expressed in Southern France from the seeds of the sesame plant, which is grown in the Levant, India, Japan, and West Africa. A representative sample gave the following results:—

+---------+--------------+------+-----------+------+----------+ | Specific| | |Acidity (as| |Refractive| | Gravity |Saponification|Iodine|Oleic Acid)|Titre,| Index at | |at 15° C.| Value. |Value.| per cent. | °C. | 20° C. | +---------+--------------+------+-----------+------+----------+ | 0·9227 | 190 | 110 | 1·84 | 22·8 | 1·4731 | +---------+--------------+------+-----------+------+----------+

=Palm-Nut Oil (Palm-Kernel Oil).=—This oil is obtained by expression or extraction in Europe from the kernels of the palm-tree fruit imported from Africa. It very closely resembles cocoanut oil in character and is used for similar purposes. The following results were obtained with normal samples of English and Hamburg oils respectively:—

+----------------+-----------------+--------+------------+ | | Acidity | | Refractive | | Saponification | (as Oleic Acid) | Titre, | Index at | | Value. | per cent. | °C. | 20° C. | +----------------+-----------------+--------+------------+ | 245 | 4·4 | 24 | 1·4553 | | 243 | 7·7 | 23·8 | 1·4553 | +----------------+-----------------+--------+------------+

=Sunflower-Seed Oil= is expressed from sunflower seeds, the principal source of which is Southern Russia and Caucasia. It is also intended to cultivate them in South Africa, recent experiments having been found satisfactory. The following figures were obtained with a typical sample of the oil:—

+----------+----------------+--------+-----------------+--------+ | Specific | | | Acidity | | | Gravity | Saponification | Iodine | (as Oleic Acid) | Titre, | |at 15 °C. | Value. | Value. | per cent. | °C. | +----------+----------------+--------+-----------------+--------+ | 0·9259 | 191 | 126·2 | 0·81 | 17 | +----------+----------------+--------+-----------------+--------+

=Cacao Butter=, =or Oil of Theobroma=, is expressed from the beans of Theobroma Cacao, which is grown in Central America, and is the source of ordinary cocoa. It is used in pharmacy, but is principally employed in the manufacture of chocolate cream (vide Chapter VII. p. 84), the supply of which is very much inferior to the demand. It is a yellowish white, brittle solid, at the ordinary temperature, bleaching with age, and the following figures are typical of those given by an average sample:—

+----------------+-----------------+--------+--------+ | | Acidity | | | | Saponification | (as Oleic Acid) | Titre, | Iodine | | Value. | per cent. | °C. | Value. | +----------------+-----------------+--------+--------+ | 193 | 1·1 | 47·9 | 33·6 | +----------------+-----------------+--------+--------+

=Palm Oil.=—This is obtained from the fruit of the palm trees grown extensively along the West Coast of Africa. There are many qualities, that from Lagos being the best. The oil is occasionally employed in the manufacture of margarine, to which it imparts a yellow colour. Its use was recently the subject of an action in the United States Supreme Court, the decision of which was that palm oil must be regarded as an artificial colouring matter, and must pay duty as such, even if used as a material ingredient to improve the wholesomeness and flavour of the product.

=Soya Bean Oil=, expressed in China from the Soya bean, is now coming extensively into use, and is already employed for culinary purposes. It has, according to De Negri and Fabris, the following properties:—

+-----------------+----------------+--------+ |Specific Gravity | Saponification | Iodine | | at 15° C. | Value. | Value. | +-----------------+----------------+--------+ | 0·9242 | 191 | 121·3 | +-----------------+----------------+--------+

The three following are among the more recently discovered oils, and are now sometimes used in the preparation of vegetable butter:—

=Shea Butter.=—This is extracted from the kernels of the Bassia Parkii, grown in Africa and Eastern India. It is somewhat tough and sticky, and has the following properties:—

+---------------+-----------------+--------+------------+ | | Acidity | | Refractive | |Saponification | (as Oleic Acid) | Titre, | Index at | | Value. | per cent. | °C. | 60° C. | +---------------+-----------------+--------+------------+ | 181 | 8·2 | 53·2 | 1·4566 | +---------------+-----------------+--------+------------+

=Mowrah-Seed Oil.=—This oil, obtained from the seeds of Bassia longifolia and Bassia latifolia, is largely imported into this country from India. It gives the following figures on analysis:—

+---------------+-----------------+--------+------------+ | | Acidity | | Refractive | |Saponification | (as Oleic Acid) | Titre, | Index at | | Value. | per cent. | °C. | 60° C. | +---------------+-----------------+--------+------------+ | 187 | 10 | 43·4 | 1·4518 | +---------------+-----------------+--------+------------+

=Margosa Oil.=—This is prepared from the seeds of Melia azedarach, a tree found in most parts of India and Burmah. According to Lewkowitsch (Analyst, 1903, pp. 342-344) it has the following analytical characteristics:—

+----------------+--------+--------+
| Saponification | Iodine | Titre, |
| Value. | Value. | °C. |
+----------------+--------+--------+
| 196 | 69·6 | 42 |
+----------------+--------+--------+

Of the other raw materials mention may be made of milk, which should not contain less than 3 per cent. fat, and may be fresh or “soured”; water, which should be as pure as that of a drinking supply; salt (sodium chloride), which is readily obtainable in a very pure state; and colouring matter, which generally consists of annatto.

CHAPTER III

REFINING, BLEACHING, AND DEODORISING FATS AND OILS

Physical Methods—Washing, freezing, filtration, treatment with charcoal and fuller’s earth, steaming. Chemical methods—Caustic soda, sodium carbonate and silicate, alkaline earths, ozone, hydrosulphites, sodium bisulphite, organic peroxides.

Although, as was pointed out in Chapter II., too much stress cannot be laid upon the importance of using only the freshest materials of the best possible quality in the manufacture of edible fats, yet even these frequently require a certain amount of preliminary treatment in order to bleach, deodorise, or refine them and render them palatable for human food. Numerous processes, both physical and chemical, have been devised, and in many cases patented, for these different purposes, and the following is a summary of the more important ones.

=Physical Methods.=—Among the physical methods employed may be mentioned washing with hot water, the removal of suspended matter by settling or filtration, and of excess of stearin by subjection to low temperatures, bleaching by filtration through animal charcoal or fuller’s earth, and deodorising by injecting steam either at atmospheric pressure, in vacuo, or in presence of an indifferent gas.

The impurities in freshly expressed oil which are partly in suspension and partly in solution, consist chiefly of dirt, fragments of vegetable fibre, and mucilaginous and albuminous substances. A portion of them rapidly deposits when the oil is allowed to stand, and the upper liquid may then be drawn off from the sediment and subjected to filtration or to further refining processes.

In some cases a simple filtration, after standing for a short time, is sufficient to render the oil brilliant, but special treatment is necessary when a large proportion of albuminous matter is present, since such oils either pass through the filter without becoming bright, or if a closer filtering medium is used, the pores of the filter speedily become clogged.

Various methods are employed to coagulate or precipitate albuminous matters before filtration, such as dry heat, or the introduction of fine jets of steam, or the addition of a small quantity of insoluble powder (e.g. fuller’s earth or kieselguhr), which as it subsides attracts and carries down simultaneously the particles of the gum-like mucilage.

The formation of an insoluble precipitate within the oil answers the same purpose. Thus, in Linde’s process a small quantity of milk is introduced and the mixture heated so as to coagulate the casein, the subsidence of which removes at the same time the substances that cause turbidity in the oil.

Other substances, such as solutions of tannin, are used in the same way in refining oils for technical purposes, but are inadmissible in the case of edible oils.

In the removal of dissolved impurities, alkali solutions, milk of lime, or magnesia are reagents in common use, while dilute sulphuric acid is employed to clarify linseed and certain fish oils for industrial uses.

To facilitate the purification of oils by washing with water, Dubovitz has recently recommended the addition to the water of aluminium sulphate, in the proportion of about ¾ oz. to 220 gallons per degree of hardness. This forms with the lime in the water a bulky, colloidal precipitate, which serves to bleach and clarify the oil.

=Removal of Stearin.=—When certain oils are exposed to a low temperature they become turbid and in some cases give a white deposit. This consists of glycerides of the more solid fatty acids, and is known as “stearin,” and its formation is frequently regarded as objectionable, notwithstanding the fact that when the oil is gently heated the stearin is redissolved.

In the preparation of the best edible oils, therefore, a process of chilling followed by filtration is often employed in order to remove part of the stearin, and the oils thus treated may then be exposed to a low temperature without giving a further deposit.

Oils treated in this way are commonly known as “winter oils,” and those which will only keep brilliant at the ordinary summer temperature are termed “summer oils.”

The solid fat separated in this way from cotton-seed oil is known as cotton oil stearin, although it is quite free from stearic acid. A similar process is employed for the separation of cocoanut and palm-nut oils into their respective stearins and oleins (see Chocolate Fats).

=Methods of Filtration.=—The types of filter press used in the filtration of oils are very varied. A common form consists of a hydraulic press containing a series of communicating plates with rims raised so as to form a space into which filter cloths may be fitted.

In other forms of apparatus the oil is introduced from below into a chamber, and rises upwards through the filtering medium into a compartment in which a partial vacuum has been created. Or methods of centrifugal filtration may be employed, as in apparatus in which the oil is introduced into a revolving chamber with a perforated wall round which is wrapped a filtering cloth. The oil is flung against the wall of the revolving chamber in a fine state of division, and passes through the filtering medium into an outer chamber, whence it can be drawn off.

The materials used as filtering media include sand, kieselguhr, Spanish clay, fuller’s earth, animal charcoal, paper pulp, and a mixture of wool and vegetable fibres disintegrated into a pulp.

=Chemical Methods.=—The number of chemicals employed in refining oils and fats for edible purposes is necessarily very limited. It is of course very objectionable to employ any reagent which is poisonous, though the use of barium oxide has been patented by Rocca (Fr. Pat. 325,381, 1902), and processes involving the use of mineral acids are, in general, inadmissible, as they spoil the flavour of the oil. The chief reagents employed are caustic soda (sodium hydroxide), sodium carbonate, sodium silicate, calcium or magnesium oxide, ozone, hydrosulphites, formaldehyde-sulphoxylates, and organic peroxides.

Caustic Soda.—Of the alkaline refining process the treatment of cotton-seed oil with a solution of sodium hydroxide or potassium hydroxide is the best example. The oil is mechanically agitated with the alkali solution, which usually has a specific gravity of about 1·10, either with or without the aid of heat, and the mixture then allowed to stand until it separates into two layers, the lower of which contains a sediment of impurities. This is drawn off, and the treatment repeated, but this time with a more dilute solution of alkali, and finally the oil thus clarified is washed with water to remove the excess of alkali.

In this process of refining not only are the albuminous and resinous matters precipitated, but the free fatty acids in the oil are neutralised, and accordingly freshly prepared cotton-seed oil is almost neutral in its reaction, and has a bland taste. The treatment also removes a large proportion of the colouring matter separated from the seed in the expression of the oil, and changes the dark-brown colour of the crude product to a light-golden tint.

The residue left from the refining of cotton-seed and other oils is a thick deposit containing the impurities in a concentrated form, together with a considerable proportion of oil; such residues are known as “foots,” and are utilised in the manufacture of soap.

The amount of caustic soda required depends on the degree of acidity of the oil, which it should be just sufficient to neutralise. The acidity of the oil is therefore first determined, as described in Chapter VIII., and the quantity of caustic soda calculated which will neutralise the given bulk of oil to be treated. The following is a more detailed account of the process:—

The calculated quantity of alkali is dissolved in water, the solution diluted to 12 or 15° Tw. (8° or 10° B.), and one-third of it added, either in a fine stream, or through a sprinkler, to the oil contained in a steam-jacketed tank. The mixture is now heated first to 100° F., and then gradually to 120° F., the whole being well agitated mechanically, or by blowing a current of air through a pipe inserted to the bottom of the tank.

After about fifteen minutes the agitation is stopped, and the oil allowed to rest for some time, preferably overnight, to allow the soap and impurities to settle down to the bottom, whence they may be drawn off. This treatment is then repeated a second and third time, with the same quantity of caustic soda solution, but usually of weaker strength, and in exactly the same manner as just described, after which a clear, yellow oil should be obtained.

The agitation with air must not be unduly prolonged, as this tends to oxidise the oil, raising its specific gravity and refractive index, and also injuring its flavour.

Treatment with caustic soda solution is also frequently employed for refining other vegetable oils, notably cocoanut oil. In all cases the principle is the same, viz., combination of the alkali with the free fatty acids to form soap, which on settling carries down with it colouring matter and other impurities. Only a weak solution, of say 12° Tw. (8° B.), should be used, and the quantity added should not be more than sufficient to neutralise the free acid, since otherwise some of the neutral oil may be saponified.

Sodium Carbonate.—This may be employed instead of caustic soda to neutralise the free fatty acids of an oil or fat. In practice, however, it is less frequently used by itself for refining purposes, though there is less risk of saponification of the neutral oil if a slight excess is added with this reagent than with caustic soda.

A process has been patented in France by G. Muller (Fr. Pat. 334,366, 1903) for the treatment of cacao butter with sodium bicarbonate. The fat is heated with sodium bicarbonate and water, then cooled with constant agitation until it congeals, allowed to stand for twenty-four hours, and finally subjected to a process of pressing and kneading. The fat thus treated is claimed to be softer and less brittle.

Sodium Silicate.—This is an alkaline salt, and its action is very similar to that of sodium carbonate. Its use for bleaching oils and fats has been patented by Godard (Eng. Pat. 22,085, 1903), who mixes the oil with sodium silicate, separates the soap formed, and then deodorises the neutral oil by means of steam in a fine state of division.

Alkaline Earths.—Lime and magnesia are sometimes used for removing the free fatty acids from oils and fats, insoluble calcium and magnesium soaps being formed. In Rocca’s patent, to which reference has already been made (vide supra), the oil is first neutralised with caustic soda or sodium carbonate, decanted from the resulting soap, a small quantity of strong acid added to decompose any soap remaining, and the oil finally neutralised with lime, magnesia, or baryta.

Fresenius (Eng. Pat. 19,171, 1902) neutralises the oil with caustic soda, lime, or magnesia, under a pressure of 2 or 3 atmospheres, either in the presence of carbon to prevent oxidation, or according to a later process in an atmosphere of an inert gas. The increased pressure is claimed to facilitate the separation of the soap emulsion.

=Bleaching of Oils.=—The colouring matter of crude oils consists of chlorophyll, which gives them a greenish tinge, or of substances frequently of a resinous nature, which impart a brown colour.

In the case of some oils, such as olive oil, the natural greenish tint is allowed to remain, but the dark colour of certain other crude oils has to be reduced before the product is saleable.

As was mentioned above, treatment with alkali removes from cotton-seed oil a large proportion of the dark colouring matter at the same time as the constituents that cause turbidity.

The methods in which fuller’s earth or milk is used to refine oils have also some effect in producing a filtrate of lighter colour, while a treatment with freshly prepared animal charcoal is effective as a decolorising process in some cases.

Charcoal.—Bleaching with charcoal may be effected by mixing the oil with 1 to 5 per cent. of animal charcoal, in a granular form, warming for a short time, and filtering through a filter press. The bleaching action of animal charcoal, attributed by Knecht to the presence of nitrogen compounds, is greater in the presence of acid.

Crude charcoal requires preliminary treatment before use for bleaching purposes. It should be well boiled, first with pure water, and then after the addition of sufficient sodium carbonate or hydroxide to render it alkaline. It is next washed free from alkali, and boiled for twelve hours with four times its weight of a mixture of equal parts of commercial hydrochloric acid and water, after which it is washed free from acid, dried, and burned in closed vessels. A good bleaching charcoal is thus obtained.

EDIBLE FATS AND OILS

THEIR COMPOSITION, MANUFACTURE AND ANALYSIS

PREFACE

CONTENTS

INDEX 145

EDIBLE FATS AND OILS

CHAPTER I

INTRODUCTION

CHAPTER II

RAW MATERIALS USED IN THE MANUFACTURE OF EDIBLE FATS AND OILS

CHAPTER III

REFINING, BLEACHING, AND DEODORISING FATS AND OILS