CHAPTER IX_Edible fats and oils

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.

----------+----------------+------------------+------+-------+------

| | | | |

Glyceride| Formula. |Chief Occurrence. | (A) | (B) | (C)

| | | | |

----------+----------------+------------------+------+-------+------

| | |at -60| |

Caproin |C₃H₅(OC₆H₁₁O)₃ |Cocoanut and | -25 |1·42715| 128·7

Caprylin |C₃H₅(OC₈H₁₅O)₃ |Cocoanut and | -8·3 |1·43316| 156·7

Caprin |C₃H₅(OC₁₀H₁₉O)₃ |Cocoanut and | 31·1 |1·43697| 184·7

Laurin |C₃H₅(OC₁₂H₂₃O)₃ |Cocoanut and | 45 |1·44039| 212·7

Myristin |C₃H₅(OC₁₄H₂₇O)₃ |Nutmeg butter, | 56·5 |1·44285| 240·7

| | | | |

| | oils. |at -6 | |

----------+----------------+------------------+------+-------+------

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.

_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.

_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_

----------------+-------------+------------+------------------------

| | Melting |

Acid. | Formula. | point, °C. | Found in--

----------------+-------------+------------+------------------------

Acetic | CH₃COOH | 17 | Macassar oil.

Butyric | C₃H₇COOH | | Butter, macassar oil.

Isovaleric | C₄H₉COOH | | Porpoise and dolphin

| | | oils.

Caproic | C₅H₁₁COOH | | Butter, cocoanut oil.

Caprylic | C₇H₁₅COOH | 15 | Butter, cocoanut oil,

| | | Limburg cheese.

Capric | C₉H₁₉COOH | 30 | Butter, cocoanut oil.

Lauric | C₁₁H₂₃COOH | 44 | Cocoanut oil, palm

| | | kernel oil.

Ficocerylic | C₁₂H₂₅COOH | | Pisang wax.

Myristic | C₁₃H₂₇COOH | 54 | Nutmeg butter, liver

| | | fat, cocoanut oil,

| | | dika fat, croton oil.

Palmitic | C₁₅H₃₁COOH | 62·5 | Palm oil, most animal

| | | fats.

Daturic | C₁₆H₃₃COOH | | Oil of Datura Stamonium.

Stearic | C₁₇H₃₅COOH | 69 | Tallow, lard, most

| | | solid animal fats.

Arachidic | C₁₉H₃₉COOH | 75 | Arachis or earth-nut

| | | oil, rape and mustard

| | | seed oils.

Behenic | C₂₁H₄₃COOH | | Ben oil, black mustard

| | | seed oil, rape oil.

Lignoceric | C₂₃H₄₇COOH | 80·5 | Arachis oil.

Carnaubic | C₂₃H₄₇COOH | | Carnauba wax.

Pisangcerylic | C₂₃H₄₇COOH | | Pisang wax.

Hyænic | C₂₄H₄₉COOH | | Hyæna fat.

Cerotic | C₂₅H₅₁COOH | 78 | Beeswax, China wax,

| | | spermaceti.

Melissic | C₂₉H₅₉COOH | 89 | Beeswax.

Psyllastearylic | C₃₂H₆₅COOH | | Psylla wax.

Theobromic | C₆₃H₁₂₇COOH | | Cacao butter.

----------------+-------------+------------+------------------------

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_

------------+------------+------------+-----------------------------

| | Melting |

Acid. | Formula. | point, °C. | Found in—

------------+------------+------------+-----------------------------

Tiglic | C₄H₇COOH | 64·5 | Croton oil.

Moringic | C₁₄H₂₇COOH | | Ben oil.

Physetoleic | C₁₅H₂₉COOH | 30 | Sperm oil.

Hypogæic | C₁₅H₂₉COOH | 33 | Arachis and maize oils.

Oleic | C₁₇H₃₃COOH | 14 | Most oils and fats.

Rapic | C₁₇H₃₃COOH | | Rape oil.

Doeglic | C₁₈H₃₅COOH | | Bottle-nose oil.

Erucic | C₂₁H₄₁COOH | 34 | Mustard oils, marine animals

| | | rape oil.

------------+------------+------------+-----------------------------

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_

+-------------+------------+---------+-----------------------+

| | | °C. | |

+-------------+------------+---------+-----------------------+

+-------------+------------+---------+-----------------------+

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_

+-------------+------------+----------------------+

| Acid. | Formula. | Found in— |

+-------------+------------+----------------------+

|Linolenic | C₁₇H₂₉COOH | Linseed oil. |

|Isolinolenic | C₁₇H₂₉COOH | Linseed oil. |

|Jecoric | C₁₇H₂₉COOH | Cod-liver and marine |

| | | animal oils. |

+-------------+------------+----------------------+

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_

+-----------+----------------+---------+-------------+

| | | °C. | |

+-----------+----------------+---------+-------------+

+-----------+----------------+---------+-------------+

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:—

+-----------------+----------------+-----------------+--------+

+-----------------+----------------+-----------------+--------+

|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 |

| | | | |

|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:—

+--- -------+----------------+-------------+--------+------------+

| | 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:—

+---------+--------------+------+-----------+--------+----------+

|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:—

+---------+--------------+------+-----------+------+----------+

|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:—

+----------------+--------+-----------------+--------+

+----------------+--------+-----------------+--------+

| 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:—

+----------------+--------+-----------------+--------+------------+

+----------------+--------+-----------------+--------+------------+

| 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:—

+---------+--------------+-------+-----------+------+----------+

|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:—

+---------+--------------+------+-----------+------+----------+

|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:—

+----------------+-----------------+--------+------------+

| 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:—

+----------+----------------+--------+-----------------+--------+

+----------+----------------+--------+-----------------+--------+

| 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:—

+----------------+-----------------+--------+--------+

+----------------+-----------------+--------+--------+

| 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:—

+---------------+-----------------+--------+------------+

| 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:—

+---------------+-----------------+--------+------------+

| 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.

_Fuller’s Earth._—Fuller’s earth (aluminium magnesium hydrosilicate)

should be dehydrated by roasting prior to use, in order to secure the

best results. The quantity required varies from 2-5 per cent. for

cocoanut, palm-kernel, and olive oils, to upwards of 10 per cent. for

arachis and cotton-seed oils, and the oil should be thoroughly mixed

with the reagent and maintained at a temperature of say 100° F. for

about fifteen minutes, and then filtered through a filter press. The

fuller’s earth retains about 80 per cent. of the oil, which may be

extracted by means of a solvent, the latter distilled off, and the

recovered oil treated with a fresh quantity of fuller’s earth. The

spent fuller’s earth may be “regenerated” by heating it up to 400-500°.

Fuller’s earth is frequently used in America for the filtration of

“premier jus.”

According to Hirzel (_Chem. Rev. Fett- u. Harz-Ind._, 1904, 116-118;

145-146), the earthy flavour sometimes remaining after contact with

fuller’s earth may be removed by washing with 10 per cent. of a 10 per

cent. solution of brine, and by adding 1 to 1½ per cent. of powdered,

dry sodium bicarbonate.

Godard (Eng. Pat. 22,086, 1903) carries out the agitation with reagents

_in vacuo_ in order to prevent oxidation of the oil.

No very definite details as to the quantity of charcoal or fuller’s

earth to be used, the temperature to which the oil should be raised in

contact with them, and the time it should be maintained thereat, can be

given, as these vary considerably for different oils, and can only be

determined by actual experiments with the particular oil it is required

to bleach.

The use of finely divided alumina, bauxite, or magnesite previously

ignited at a low temperature, has also been patented for decolorising

oils, and a process for the recovery of spent decolorising materials

(which consists in mixing them with salt water, heating the mixture

to about 85° C. with sulphuric acid, then treating it with sodium

carbonate and mechanically agitating it for a short time) has been

patented by the Soc. Anon. Huilerie et Savonnerie de Lurian (Fr. Pat.

499,915, 1909). The carbon dioxide liberated by this treatment carries

the oil to the surface.

Methods in which chlorine or bleaching powder are employed are only

applicable for bleaching oils intended for the making of soap or other

technical purposes, owing to the reagent attacking the glycerides and

imparting a flavour. For similar reasons Watts’ bichromate process of

bleaching palm oil is also unsuitable for the treatment of fat intended

for food.

Methods of oxidation, either by means of hot air passed through

the heated oil or fat, or by means of ozone or ozonised air, under

controlled conditions, are employed both to obtain paler oils and to

remove substances of unpleasant odour.

The bleaching of beeswax by exposing it in thin strips to the action

of air and sunlight has long been practised, and Japan wax is also

rendered nearly white by similar means.

The use of artificial light in place of sunlight is claimed in several

patents for bleaching oils, such as cotton-seed oil. The oil is made

to pass across a transparent surface through which are transmitted the

rays from a powerful arc light.

Ultra-violet rays, such as those emitted by the mercury vapour lamp,

are employed as the bleaching agent in similar processes.

_Ozone._—The use of ozone as a bleaching agent has long been known, but

its application to the treatment of oils and fats has hitherto met with

little success. It has been the subject of many patents, among which

may be mentioned that of Andreoli (Eng. Pat. 14,570, 1898), who makes

use of the joint action of ozone and a hypochlorite solution, and that

of J. Harris (Eng. Pat. 22,430, 1906). Harris first ozonises the oil at

a temperature of 100° to 180° F. for fifteen to thirty minutes, until

there is an appreciable rise—say 0·5 per cent.—in the free fatty acids.

The treatment with ozone is then stopped, and the oil neutralised with

alkali, preferably an aqueous solution of caustic soda at about 15° Tw.

(10° B.). The impurities are next separated, and the oil dried by means

of a current of air while warm, after which it may be still further

refined by heating it with 5 per cent. of aluminous earth, followed by

filtration.

This latter process seems to be rather a mistaken one, as from

experiments made by one of the authors (S.), the best results are

obtained when the ozonisation is only carried to such a point that

there is no appreciable increase in the free acidity of the oil.

Recent experiments by him on the bleaching and deodorising action of

pure ozone _free from nitrogenous compounds_, as obtained with the

Ozonair apparatus, have given results which are most promising. Palm

oil, even of the crudest description, has been most effectively and

cheaply bleached by merely passing a strong current of ozonised air

through it, and the colour of certain other vegetable oils has been

distinctly improved by this treatment; while in the case of a very acid

sample of cocoanut oil, the fat was not only made whiter in colour, but

had also almost entirely lost its characteristic odour. Hence there

seems to be a likelihood of the successful employment of the ozone

process for this purpose in the future.

_Hydrosulphites_ or “hyposulphites.”—Sodium hydrosulphite, obtained

by digesting a concentrated solution of sodium bisulphite with zinc

dust or turnings, is a powerful reducing agent, and has been patented

as a means of bleaching oils and fats by Metz and Clarkson (Eng. Pat.

11,983, 1906). It is particularly applicable to maize oil, which may

be bleached by agitating 200 parts of the oil with 600 parts of water

and 15 parts of sodium hydrosulphite for ten hours in a closed vessel,

allowing the mixture to stand for thirty-two hours, and then separating

the oily layer.

Sodium hydrosulphite formaldehyde, which was shown by Baumann, Thesmar,

and Frossard in 1904 to be commercially a mixture in almost equal

proportions of sodium sulphoxylate formaldehyde and sodium bisulphite

formaldehyde, is also recommended for the purpose, the oil being heated

to 70° C. with this reagent in a closed vessel, and then allowed to

stand.

The formaldehyde-sulphoxylates are now sold under a variety of fancy

names, the sodium compound being termed _Rongalite C._ and _Hydraldite

C._, and the zinc salt _Decroline_.

_Sodium Bisulphite._—This salt, which possesses the property of

combining with aldehydes, has been utilised in some cases for

deodorising oils and fats, with good results.

_Organic Peroxides._—The Vereingte Chem. Werke have recently patented

the use of various organic peroxides (such as those of benzoyl, acetyl,

and acetone, together with the oxidation products obtained by the

action of nitrogen tetroxide on organic compounds) for the bleaching of

oils and fats. The oil is heated to 100° C. with about 0·2 per cent. of

the peroxide, and allowed to stand in a warm place for a short time,

until bleaching has taken place.

There is now a large number of per-salts available, _e.g._,

persulphates, percarbonates, perborates, which are being utilised for

various bleaching purposes, but so far they do not appear to have been

employed to any appreciable extent in the treatment of oils and fats,

though ammonium persulphate (palidol) is now being used for bleaching

soap in the pan.

=Deodorisation of Fats.=—The odours of oils and fats are due to the

presence of small quantities of volatile substances, either derived

from the vegetable substance as in the case of maize and wheat oils, or

formed by slight decomposition of the oil itself.

It is chiefly in connection with cocoanut oil, which forms the basis of

so many vegetable lards and butters, that the problem of deodorisation

of a fresh fat has to be faced.

According to the recent research of Haller and Lassieur (_Comptes

Rend._, 1910, 150, 1013), the unpleasant odour of commercial cocoanut

oil must be attributed, partly to a process of decomposition of the

glycerides, with the liberation of fatty acids (caproic, caprylic,

capric acids, etc.) with a pronounced odour; and partly to the

presence of certain substances, which include methyl-heptyl ketone

and methyl-nonyl ketone. Traces of these may also be detected in the

refined fat, and account for its odour when heated. The substances

to which the odour is due may be obtained in the form of an essence

(échappés) by distilling the cocoanut oil in a current of superheated

steam.

Speaking broadly, two methods only have so far been discovered, or,

at any rate, published, for the deodorisation of cocoanut oil—(1)

washing out of the odoriferous bodies with alcohol, and (2) their

volatilisation by treatment with steam. Other unpublished processes

are doubtless used by some manufacturers, but their secrecy is very

jealously guarded.

The washing of cocoanut oil with alcohol of course removes free fatty

acids, which are soluble therein. This method of treatment was first

introduced by Chevreul, and has been also utilised by Schlinck, who

employed a joint process of washing with alcohol and treatment with

charcoal. A special apparatus for its application was patented by

Urbain and Feige (Fr. Pat. 361,966, 1905), consisting of a series of

vessels so arranged that the oil descends from vessel to vessel, and

meets hot alcohol circulating in the opposite direction, so that the

more impure oil comes in contact with the more impure alcohol. The

temperature is maintained at 70° C. during the treatment, and means are

provided for evaporating and condensing the alcohol after extraction is

complete.

An improvement upon this patent has been since protected by the

patentees, in which sufficient alkali is added to combine with the free

fatty acids prior to the extraction with alcohol.

With so volatile a substance as alcohol, there is necessarily a

considerable loss by evaporation during working, and the cost of

alcohol in this country is too high for the process to be economical.

The treatment of cocoanut oil with steam in order to deodorise it dates

back to 1882, when a process was patented in Germany by Jeserich and

Meinert, in which the volatile fatty acids were first driven off by

passing high pressure steam at 6 to 8 atmospheres into the fluid oil,

with constant stirring for about two or three hours, after which steam

was shut off, and the non-volatile fatty acids separated by addition of

0·25 per cent. of calcined magnesia, the magnesium soap formed rising

to the surface, whence it could be skimmed off.

Several modifications of this process have since been patented.

Klimont (Eng. Pat. 3164, 1902) neutralises the oil with alkali prior

to treatment with superheated steam, and then removes non-volatile

impurities by either raising the temperature of the oil to above 100°

C., treating it with calcium or magnesium hydroxide, or extracting

it with some solvent such as acetone, which dissolves the oil and

precipitates the impurities.

The Fabrique de Prod. Chim. de Thann et de Mulhouse treat the oil with

steam in the absence of air, either _in vacuo_, or in an atmosphere of

an indifferent gas.

In another method of deodorisation cocoanut oil is freed from its

more fluid constituents (as in the preparation of chocolate fats,

_q.v._) and the fatty acids eliminated in the form of calcium salts by

treatment with lime; sodium silicate is employed in another process

as the means of removing the fatty acids. Yet however carefully the

odoriferous substances may have been removed, the readiness with which

cocoanut oil undergoes hydrolysis, and the nature of the fatty acids

contained in its glycerides, renders this fat particularly liable to

acquire an odour again, after having been exposed for a short time to

the air.

=Treatment of Rancid Fats.=—Although the practice is to be condemned,

it is not uncommon for fats that have become slightly rancid to be

subjected to treatment to eliminate the compounds to which rancidity is

due, and thus enable the fat to be blended with fresh fats.

In the development of the changes understood by the term “rancidity,”

the glycerides undergo hydrolysis with the liberation of fatty acids,

which are in turn decomposed or oxidised, with the formation of various

compounds such as fatty anhydrides, aldehydes, and hydroxy acids.

These changes are brought about under the influence of light and

atmospheric oxidation, and are probably promoted by enzymic action or

by the influence of micro-organisms when albuminous substances have

been left in the fat.

The removal of free fatty acids is frequently sufficient to make the

oil appear fresh. This may be effected by mechanically agitating

the fat with a suitable proportion of milk of lime or magnesia,

which combine with the free fatty acids to form insoluble calcium or

magnesium soap, which can readily be separated by filtration.

Neutralisation with caustic alkali (as in the refining of cotton-seed

oil) or with a solution of sodium silicate, also effects the removal

of free fatty acids, but the latter reagent is liable to produce an

obstinate emulsion when employed on a large scale.

In another process the rancid oil is treated with a suitable proportion

of precipitated chalk, and is subsequently filtered while hot through a

layer of animal charcoal.

Reference has already been made to the method of dissolving out the

free fatty acids by means of alcohol. Oils in which a process of

hydrolysis has once started are liable, after removal of the free fatty

acids, not to keep so well as freshly expressed products.

Rancidity may be present in an oil without the liberation of free fatty

acids, though, as a rule, the acid value of a fat will afford some

index of the degree of rancidity, since the development of acidity and

of rancidity are often simultaneous.

For the removal of the aldehydic compounds formed in the changes that

occur, a treatment with a strong solution of sodium bisulphite is used

in a process described by Nagel, while volatile products are expelled

by heating the oil in a current of steam at gradually increasing

temperatures.

Other reagents used for sweetening rancid oils are a solution of

ordinary salt, dilute (1 per cent.) sulphuric acid, a solution of myrrh

in methyl alcohol, etc.

As a rule, the different processes are employed successively, and

followed by filtration and drying of the oil.

The tendency of an oil to become rancid depends largely upon the

proportion of volatile fatty acids and unsaturated fatty acids it

contains. Thus butter and cocoanut oil readily turn rancid, whereas

beef stearin and cacao butter will keep for a long time unaltered.

Any oil or fat is best protected from rancidity by keeping it in the

dark in a vessel from which all air is excluded. Rancidity will take

place in the dark, but much less rapidly than when the fat is exposed

to light. This is due to the accelerating effect of light upon the

action of oxygen. Heat has also a pronounced influence in promoting

chemical changes in oils, and cold has a retarding influence, although

it does not stop the oxidation.

The odour of rancid fats that do not (like cocoanut oil) contain

volatile fatty acids is due to the formation of aldehydes or of esters,

the latter being probably produced, in some cases at all events, by the

action of certain micro-organisms upon the liberated glycerin.

Rancidity is accompanied by a decrease in the iodine value of the fat,

which is due to the absorption of oxygen by the unsaturated bonds of

the liquid fatty acids. A determination of this value may therefore, in

some cases, give indications of the freshness of a fat.

A more promising method, however, is to distil the fat in a current of

steam, and to estimate the amount of aldehydes in the distillate.

CHAPTER IV

BUTTER

=Butter Fat.=—The fat contained in suspension in the milk of mammals

differs considerably in chemical composition from the body fat of the

same animals. The latter consists mainly of glycerides of the higher

fatty acids, notably stearic, palmitic, and oleic acids in varying

proportions, whereas in the case of milk fats there is in addition to

compounds of these fatty acids a large proportion of glycerides of

volatile fatty acids.

It is upon this characteristic feature of butter fat that many of the

methods of detecting foreign fats in butter are based.

A specimen of butter fat examined by Brown yielded 86·40 per cent. of

insoluble fatty acids and 8·35 per cent. of soluble volatile fatty

acids. The former included 32·85 per cent. of oleic acid, 1·83 per

cent. of stearic acid, 38·61 per cent. of palmitic acid, 9·89 per

cent. of myristic acid, and 2·57 per cent. of lauric acid. The soluble

volatile acids were made up of 5·45 per cent. of butyric acid, 2·09 per

cent. of caproic acid, 0·49 per cent. of caprylic acid, and 0·32 per

cent. of capric acid.

The low proportion of stearic acid found was in accordance with the

direct estimations made by Hehner and Mitchell, who obtained only small

amounts in their examination of the fatty acids from a large number of

samples of butter fat of different origin. It was interesting to note,

however, that after the fatty acids had been exposed to the air for

some weeks, there was apparently a gradual formation of stearic acid.

The general composition of butter fat, as shown by the examination of

Brown (_supra_), is as follows:—

+----------------------+-----------+

| Glycerides of— | Per Cent. |

+----------------------+-----------+

|Dihydroxystearic acid | 1·04 |

|Oleic acid | 3·95 |

|Stearic ” | 1·91 |

|Palmitic ” | 40·51 |

|Myristic ” | 10·44 |

|Lauric ” | 2·73 |

|Capric ” | 0·34 |

|Caprylic ” | 0·53 |

|Caproic ” | 2·32 |

|Butyric ” | 6·23 |

+----------------------+-----------+

Naturally, different specimens of butter may show wide variations in

the proportions of their different constituents, but the above may be

taken as typical and as an illustration of the more complex character

of milk fat than that of a body fat.

The glycerides in butter fat are probably present in the form of mixed

glycerides, though, as yet, certain proof of this is wanting.

=Butter.=—Commercial butter consists of butter fat, water, casein, and

salt, the proportion of fat usually ranging from about 84 to 87 per

cent.

The following results obtained by Vieth (_Analyst_, 1891, xvi. 1) show

the average composition to be expected:—

+---------------------------+---------+---------+---------+---------+

+---------------------------+---------+---------+---------+---------+

|Danish (17 samples) | 83·41 | 1·30 | 1·87 | 13·42 |

|English (72 samples) | 86·85 | 0·59 | 1·02 | 11·54 |

|French (fresh, 108 samples)| 84·77 | 1·38 | 0·09 | 13·76 |

| ” (salted, 5 samples) | 84·34 | 1·60 | 2·01 | 12·05 |

|Kiel (4 samples) | 85·24 | 1·17 | 1·35 | 12·24 |

|Swedish (25 samples) | 83·89 | 1·33 | 2·03 | 13·75 |

+---------------------------+---------+---------+---------+---------+

_Water._—Statutory regulations are in force in many countries to limit

the permissible amount of water in butter. In Great Britain and Ireland

pure butter must not contain more than 16 per cent. of moisture, while

the so-called “milk-blended butter” is not allowed to exceed the limit

of 24 per cent.

The following limits are in force in other countries: _Belgium_, 18 per

cent. unless declared; _Germany_, 18 per cent. for unsalted butter and

16 per cent. for salted butter; _United States_, 16 percent.; _Canada_,

16 percent.; _Queensland_, 16 per cent.; _Victoria_, 15 per cent.

These regulations have been found necessary, owing to the readiness

with which a large excess of water (over 25 per cent.) may be churned

into a butter without making it appear abnormally moist or interfering

with its sale.

The effect of “salting” butter is to reduce the amount of moisture, as

is shown in the results of Vieth, quoted in the table given above.

Richmond considers that the best proportion for a butter that is meant

to keep well is 13·5 per cent.

_Salt._—There is no regulation as to the amount of salt that may be

added to butter, and the proportion will depend upon the popular taste;

sometimes as much as 10 per cent. may be found.

_Curd._—This term represents not only the solid nitrogenous substances

derived from the casein of the milk, but also the milk sugar, etc., and

its amount is roughly estimated by subtracting from 100 the percentages

of butter fat, moisture, and ash which have been separately determined.

The proportion thus found varies from a fraction of 1 per cent. to

about 1·75 per cent., the average being a little over 1 per cent.

More accurate estimations of the true casein are obtained by

determining the amount of nitrogen, and calculating the quantity of

casein from the result.

=Keeping Properties of Butter.=—Rogers and Gray have studied the effect

of the acidity of the cream upon the flavour of butter (U.S. Dept.

Agricult., 1909, Bull. No. 119). They show that butter is liable to

develop unpleasant flavours even when stored at temperatures as low as

-10° F., and that the amount of alteration increases with the acidity

of the cream from which the butter was prepared.

No micro-organisms to which the more rapid deterioration of butter from

very acid cream could be attributed were detected, nor did the changes

appear to be due to the action of enzymes.

When the butter had been made from sterilised cream acidified with

various acids there was a gradual development of unpleasant flavours,

and this result indicated that the acid normally produced in milk

by the lactic acid bacteria had an influence in bringing about slow

decomposition of unstable compounds in the butter.

Butter made from sweet sterilised cream was found to show much less

tendency to change on storage than that made in the ordinary way, but

the flavour would as a rule be regarded as too mild.

Flavours derived from the wood of the churn, or other external sources,

would also be much more noticeable in the case of such butter than in

that made from soured cream.

This lack of flavour has been shown by Storch to be due to absence

of the products of certain bacteria which develop in the souring of

the cream, and various species have been isolated, each imparting

characteristic properties to the butter.

Thus Conn has demonstrated the practical advantages of inoculating the

cream with cultures of specific bacteria, and has shown that in this

way it is possible to give to the butter the particular flavours which

previously had only been naturally produced at certain periods of the

year. At the same time butter thus artificially ripened was found to

keep better and to retain its flavour longer than that prepared by

the older method. This method of artificial inoculation with specific

organisms has been successfully employed on a large scale in America.

Burr and Wolff (_Milchwirtschaftl. Zentralbl._, 1910, vi. 241) have

recently studied the effect of the parchment wrappings of butter upon

the keeping qualities, and have found that under certain conditions

parchment paper affords a suitable medium for the growth of moulds.

The main factors influencing this growth are a high percentage of

moisture in the butter and the access of air. The presence of 1 to 1·5

per cent. of salt checks the growth, whereas unsalted butter is readily

attacked.

A method of improving the keeping qualities of butter has been based

upon the sterilising action of ultra-violet rays upon the water used

for washing the butter in the dairy.

It has been pertinently pointed out by Dornic and Daire (_Comptes

Rend._, 1909, 149, 355) that it avails little to prepare butter

from sterilised cream if the water used for washing it contains

micro-organisms that tend to produce rancidity.

The apparatus employed by Dornic and Daire consists of a tank lined

with glass, and provided with glass partitions over which the water

passes, and receives the rays from two quartz electric lamps, which are

inserted through holes in the cover of the tank.

About 3000 litres of water can thus be rendered practically sterile

in a day, the number of bacteria being reduced by the treatment to an

insignificant quantity.

The cream, or the butter itself, might be rendered sterile by this

process, but an unpleasant flavour produced by the action of the ozone

formed by the lamps prevents the method being successfully employed in

practice.

A French patent has, however, been taken out (No. 400,921 of 1909) for

sterilising butter or other fats in this way. The substance is spread

in a thin layer upon an endless band or revolving drum, the movement of

which carries it past a series of lamps emitting ultra-violet rays.

=Rancidity of Butter.=—There appears to be little doubt that

micro-organisms may play a part in the production of rancidity in

butter, although the presence of light and air are probably the chief

factors in the changes that take place.

Laxa, who studied the question with especial reference to butter

(_Arch. Hyg._, 1902, xli. 119), found that several mould fungi, and

at least one bacillus (_B. fluorescens liquefaciens_), were capable

of growing upon media containing butter fat and of breaking up the

glycerides, with the liberation of free fatty acids, which were then in

turn decomposed.

The acidity of the fat increases with the progress of the rancidity,

but not necessarily proportionately, and a specimen of butter fat in

which the oxidation product to which the rancid taste and odour are

due may have a lower acid value than butter, which shows no trace of

rancidity.

Many of the compounds produced in the development of rancidity are

soluble, and may be separated from the fat by washing it with water.

Advantage is taken of this fact in the preparation of “process” butter

from stale or unsaleable genuine butter.

There is no definite test that can be applied to detect rancidity in

butter, and reliance must therefore be mainly placed upon the taste.

=Renovated Butter.=—A product sold in large quantities under the name

of renovated or “process” butter is prepared by melting down the fat

of old butter, separating it from the curd and water, chilling it

upon ice, and re-churning it with fresh milk and whey. By this means

the casein is restored to the butter, and a mixture is obtained which

answers to the chemical tests for fresh butter, but lacks its fresh

flavour.

Several methods are employed for distinguishing process butter from

the genuine product, the most satisfactory of which are based upon the

physical alteration of the butter fat in the processes of melting and

congealing. Thus in the case of ordinary butter the separated fat does

not show the crystalline structure of the fat from renovated butter

when examined under the microscope, and the difference is still more

pronounced when the fats are compared in polarised light.

Other tests upon which a judgment may be based are the greater

solubility of the “process” fat in glacial acetic acid (Cochrane); and

the appearance and behaviour of the separated curd, which is gelatinous

when derived from fresh butter, and granular and flocculent when

obtained from renovated butter.

Hess and Doolittle (_J. Amer. Chem. Soc._, 1900, xxii. 150) also

observed a difference in the behaviour of the two products when heated,

genuine butter foaming, while process butter splutters in the same way

as margarine, from which, however, it may be distinguished by other

tests.

The trade in process butter is much more extensive in the United States

than in this country, and numerous patents have been taken out to

obtain a product that shall imitate ordinary butter still more closely.

Among the most recent of these is the process claimed by Roos (U.S.

Pat. 854,383, 1907). The fat separated from the old butter is melted

and heated to a temperature of 108° to 110° F., and is then termed

“butter oil.”

About five parts of it are added to 3 parts of a previously churned

mixture of acidified skimmed milk and fresh whole milk, and the

whole stirred up until an emulsion is obtained. This is treated with

cold water to cause crystallisation, and the resulting crystals are

mixed with salt and exposed to the air for some time at the ordinary

temperature, after which the mass is thoroughly kneaded to expel the

salt and the excess of milk.

=Preservatives in Butter.=—Butter that at one time was heavily salted

is now frequently preserved by the addition of a small amount of borax

or other compound of boric acid.

The prevalence of the practice was shown by the evidence given

by leading representatives of the butter industry before the

Departmental Committee on Preservatives in Food (1901). One of these

witnesses informed the Committee that his firm had ceased to use heat

sterilisation of the cream, as it was found to impair the flavour of

the butter.

It was further shown that the butter imported from Australia, Normandy,

etc., contained 0·5 per cent. of boric acid; and that this amount was

regarded by the trade as sufficient for the purpose.

In their report the Committee recommended that no preservative other

than boric acid or borax, or mixtures of the two, should be permitted

to be used in butter or margarine, and that the proportion should not

exceed ½ per cent.

An attempt was made in France to prohibit absolutely the use of

preservatives in butter, but the needs of the trade were too strong,

and, as was mentioned above, the butter imported into this country from

France is almost invariably preserved.

The presence of boron compounds is proved by melting the butter,

separating the aqueous portion, rendering it faintly acid with

hydrochloric acid, and immersing a strip of turmeric paper therein.

On drying the paper at a gentle heat a purple-red coloration, changing

to bluish black on the addition of ammonia solution, indicates the

presence of boric acid.

Tests are sometimes applied for other preservatives, such as salicylic

acid, sodium benzoate, sodium fluoride, and formalin, but these

compounds are not of common occurrence in butter.

Some years ago butter intended for export to tropical countries was

preserved by the addition of a fairly large proportion of glucose. This

practice was most common in France.

=Physical Characteristics.=—Butter fat has a specific gravity ranging

from about 0·907 to about 0·913 at 35° C., whereas the specific gravity

of the animal fats used as adulterants is considerably higher.

It has been shown by Skalweit (_J. Soc. Chem. Ind._, 1894, xiii. 54)

that these differences are most pronounced at a temperature of 35° C.,

as is illustrated by the following table:—

+-------------+---------+------------+-------------+

+-------------+---------+------------+-------------+

| 35 | 0·9019 | 0·9017 | 0·9121 |

| 50 | 0·8923 | 0·8921 | 0·9017 |

| 60 | 0·8859 | 0·8857 | 0·8948 |

| 70 | 0·8795 | 0·8793 | 0·8879 |

| 80 | 0·8731 | 0·8729 | 0·8810 |

| 90 | 0·8668 | 0·8665 | 0·8741 |

| 100 | 0·8605 | 0·8601 | 0·8672 |

+-------------+---------+------------+-------------+

The specific gravity of cocoanut oil is also greater than that of

animal fats.

_Solubility._—Butter fat is considerably more soluble than animal body

fats in various solvents, such as glacial acetic acid, alcohol, etc.,

and on this property have been based several rapid “sorting” tests for

distinguishing between pure and adulterated butter.

One of these tests, known as the _Valenta test_, gives the temperature

at which a solution of a definite quantity of the fat in a definite

quantity of hot glacial acetic acid becomes turbid on cooling the

liquid.

The following figures obtained by Chattaway, Pearmain, and Moor, show

the difference between butter and margarine:—

+-----------+----------+----------+-------+

+-----------+----------+----------+-------+

|Butter fat | 39·0 | 29·0 | 36·0 |

|Margarine | 97·0 | 94·0 | 95·5 |

+-----------+----------+----------+-------+

The natural variation in this respect between different samples of

genuine butter is thus too great to permit of the detection of small

quantities of margarine in butter.

_Refractometric Examination._—The difference in the refractive power of

butter fat and margarine is a valuable means of obtaining a preliminary

idea as to the purity of a sample of butter, and several instruments

have been specially constructed for the purpose. The most widely used

of these is termed a _butyro-refractometer_, and it is readily possible

by its means to distinguish in a few minutes between pure and grossly

adulterated butter. Here again, however, the variations in the readings

of samples of genuine butter of different origin are sometimes greater

than between a sample of pure butter and one adulterated with a small

percentage of margarine. Thus Crismer found that two pure samples of

butter fat gave readings of 45·8 and 46, while two adulterated samples

gave readings of 45·2 and 45·6 at 40° C.

=Chemical Characteristics.=—Owing to the large proportion of fatty

acids of low molecular equivalent present in butter fat, the

saponification value is naturally very high, ranging from about 219

to 240, though values both above and below these figures have been

recorded for genuine butter.

Since cocoanut oil also has a high saponification value (254 to 260),

mixtures of animal fat with that fat may readily be prepared which will

give figures within the normal limits for butter fat.

The proportion of free fatty acids in freshly churned butter fat is

very small (about 0·01 grm. per kilo. according to Duclaux), but it

gradually increases as the butter is kept. A determination of the acid

value may therefore afford some indication of the age of a sample of

butter.

The iodine value of pure butter fat is usually between 25 and 40, but

is liable to fluctuate considerably with the nature of the food given

to the cows.

Of all the different so-called constants, the Hehner and Reichert

values described below are the most important as tests of purity, and

an official method of determining the latter value has been established

in this country, so as to eliminate errors due to variations in the

size of the apparatus, duration of distillation, etc.

_Hehner and Reichert Values._—The chief substances used in the

adulteration of butter are beef fat and pig’s fat (in the form of

margarine), vegetable oils (also mainly in margarine), and (especially

of late) cocoanut oil.

The methods of distinguishing between butter fat and other animal fats

are based upon the high proportion of soluble volatile fatty acids in

the former, and their practical absence from the latter.

Originally the test was devised by Hehner, who measured the amounts of

insoluble fatty acids yielded by butter fat, and showed that they were

very much less than those given by other fats.

It is now more usual, however, to employ the more rapid process devised

by Reichert (with modifications by other chemists), in which the fatty

acids are distilled under definite conditions which must be rigidly

followed, and the proportion of them thus obtained is estimated by

neutralisation with a standard solution of alkali. The details of the

method are described at length in Chapter VIII. The result is then

expressed in the number of cubic centimetres of this standard alkali,

and is termed the Reichert (or Reichert-Meissl) value of the fat.

The Reichert-Meissl value of pure butter fat has been found to vary

under ordinary conditions from about 20 to 33, though figures far

beyond either of these limits have been recorded in exceptional cases.

In calculating the amount of foreign fat in a butter from this value

it is assumed as an arbitrary figure that an average butter fat has a

Reichert-Meissl value of 28·78, and the percentage of added fat may

thus be found approximately.

The difficulty, however, is that the values normally range so widely

above and below this average, that it is quite possible to add 10 (or

more) per cent. of foreign fat to a butter with a high Reichert-Meissl

value, and still have a product giving a normal value.

On the other hand, cows frequently produce butter which gives a value

far below the standard figure, and without special knowledge of the

conditions to which this abnormality is due the butter may be condemned

as adulterated with foreign fat.

This was shown in a striking manner a few years ago, when large

quantities of butter imported into this country from Holland were

condemned as adulterated on account of their low Reichert-Meissl values.

The causes of this abnormality were investigated by van Rijn, who

found that the mixed butter of a herd of cows might vary in its

Reichert-Meissl value from 17·0 to 32·1.

The low figures were found to coincide with the end of the pasturage

season, for after the cows had been stalled for a short time the butter

became normal again. For example, the butter from a herd of seven cows

had a Reichert-Meissl value of 24·4 on September 11, which had fallen

to 19·0 on October 23. The animals were then taken from the fields, and

their butter gave the following values: November 6, 21·5; November 20,

23·1; and December 11, 25·4.

This conclusion as to the effect of leaving the cows too late in the

fields was borne out by the results of a Commission appointed to

investigate the causes of abnormality of the butter produced in Belgium.

It was found that the butter giving such results was generally the

product of small herds of cows; that its occurrence was most pronounced

in the last four months of the year; and that with the return of spring

the values became normal again.

It may be mentioned that in Belgium the sale of butter showing a lower

Reichert-Meissl figure than 28 is prohibited by law, while in the

United States the minimum value is fixed at 24.

Poor feeding has also an influence in lowering the Reichert-Meissl

value, and to this cause must be attributed the low values frequently

found in the case of Siberian butter.

Another factor influencing the degree of the Reichert-Meissl value

is the time that has elapsed since calving. Thus it was shown by

Kreit (_Analyst_, 1893, xviii. 134) that the values obtained at an

early period of lactation were invariably higher, and that they then

gradually fell. In some cases the butter from the milk of cows that had

recently calved reached the high Reichert-Meissl value of 34·4.

This also affords the explanation of the occasionally low

Reichert-Meissl values of Irish butter, which, as has been proved by

Ball (_Analyst_, 1907, xxxii. 202), coincides with a period when the

milk has been derived from cows at the very end of lactation. This

period lasts for about six weeks, during which time the milk is richest

in fat, while the fat shows the lowest Reichert-Meissl values. Thus the

following results were obtained with butters churned on December 19,

1906:—

+---------------+---------+-------+-------+--------+----------+

+---------------+---------+-------+-------+--------+----------+

| values | 22·7 | 21·5 | 23·3 | 23·5 | 22·1 |

+---------------+---------+-------+-------+--------+----------+

The same abnormality does not occur in England, where the calving of

the cows is distributed over the whole year, instead of, as in Ireland,

taking place within six weeks of one another.

It is also possible that sufficient attention may not be given to the

cows in Ireland, since the effect of feeding and good housing is to

raise the Reichert-Meissl value of the butter, even in the case of cows

at the end of their lactation period.

=Influence of the Food of the Cows.=—The results of numerous feeding

experiments, in which quantities of different oils and fats were mixed

with the daily fodder of the cows, have shown that the nature of the

butter fat may be appreciably affected in this way. Thus Werenskiold

(_Chem. Zentralbl._, 1900, ii. 215) proved that cotton-seed oil could

be detected in the fat from the milk of cows which had taken a small

amount of cotton-seed oil cake with their food, and this result was in

agreement with the results of experiments carried out for the Board of

Agriculture in this country (_Analyst_, 1898, xxiii. 255).

As a rule, however, the colour reaction indicating the presence of

cotton-seed oil is very slight, and does not correspond to a proportion

of more than 1 per cent.

In the corresponding experiments of the Agricultural Board with sesame

oil cake the butter from the cows did not give the characteristic

colour reaction for that oil, even after they had been fed upon it for

several weeks.

There is also evidence to show that the characteristic fatty acid of

arachis oil does not pass into the milk of cows fed upon arachis-seed

cake; but it has been shown by Paal and Amberger (_Zeit. Unters. Nahr.

Genussm._, 1909, xvii. 1) that feeding the animals upon copra may have

some influence upon the composition of their milk fat, and increase the

proportion of insoluble volatile fatty acids.