WINNING WEALTH FROM SLAUGHTER-HOUSE OFFAL, CONDEMNED MEAT BONES, AND
BLOOD
Undoubtedly one of the wonders of civilization is the ability to
preserve and transport such a readily perishable foodstuff as meat in a
chilled and frozen condition for an indefinite period of time. By this
means cattle roaming the extensive ranches of North and South America,
Australia and New Zealand, are rendered available in a fresh form for
presentation upon the tables of Britain to supplement the severely
limited domestic supplies. During recent years the growth of this
traffic has been remarkable, and it will not be long before we touch
the million-tons-a-year mark for imported beef, mutton, pork, exclusive
of ham and bacon.
Yet the development of this trade has reacted directly against our
own interests. The dispatch of the carcases to these islands in the
dressed condition has deprived, and still is depriving us, of much
valuable raw material to which we should have access were we to raise
sufficient meat to satisfy our own needs. This is the exploitation of
the offal or inedible portions of the beast, the products obtained
from which are not only of marked intrinsic value, but enter into so
many other and varied industries. From this statement it must not be
imagined that we are entirely prevented from establishing a meat-waste
industry, since our domestic killing trade is of distinct significance
and is supplemented to a certain degree by the “home-killed” business.
The latter, as is well known, represents the shipment of cattle to this
country in the live condition to be slaughtered upon landing.
In these circumstances it would be perfectly feasible for us to
establish the meat residue exploitation industry upon a comprehensive
scale but for the fact that existing conditions are decisively
adverse, although we could scarcely aspire to attain the magnitude and
operations of the huge meat-packing plants of Chicago. It is extremely
doubtful if we really appreciate the possibilities of this business,
and, because of our ignorance, we, as a nation, are the losers. We have
permitted the local or territorial slaughter of cattle to be carried to
an extreme length. The municipal abattoir constitutes the feature of
the slaughtering trade of these islands, and although this practice was
introduced to overcome the shortcomings of the private slaughter-house,
which were many, and to ensure killing and dressing animals under
the most hygienic and scientific conditions, yet it is a matter for
serious consideration as to whether the municipal practice should not
be superseded by a centralized system, acting under State or private
control, the latter for preference, so as to give full rein to the
display of initiative.
There is no logical reason why the slaughter of domestic cattle
should not be conducted at a central point. Such a plant conducted
along the lines practised at Chicago would be of far-reaching benefit
to the community. Supervision would be more effective, simpler and
less expensive, inasmuch as it would be possible to dispense with
the multiplicity of officials now obtaining--another form of waste.
It would also enable the residues from the trade to be turned to
utilitarian advantage along the most economic and profitable lines,
owing to their very bulk. A visit to the Chicago stockyards brings
home very forcibly the magnitude of this trade and the wealth to be
won from the residues which accrue. It has been declared, and with
considerable truth, that at the American stockyards the development
of the by-products is every whit as extensive and as important as the
preparation of the ostensible staple product. It is actually more
profitable, and brings in as great if not greater revenue.
The arguments which would be levelled against the establishment of a
central meat-packing plant in this country are many and obvious. In
the first place full voice would be given to the apparent futility of
sending a live animal from 20 to 600 or 700 miles merely to be killed,
and to return the dressed carcase to be sold. Superficially it does
appear to be a senseless employment of transport and to incur needless
expense. Yet such a practice is followed upon the North American
continent. Animals are shipped alive over hundreds of miles to be
killed and returned to the point where they were bought, in the form
of dressed meat ready for consumption. But the argument is fatuous.
Centralized slaughtering facilities secure equitable distribution,
as well as prompt movement, since the trade is sufficiently heavy
to demand the inauguration of a special handling and transportation
system. Then again such a practice allows bulk shipment combined with
long haulage, two essential conditions to economic transportation.
If the method were practised in these islands, not only would it be
possible to take full advantage of the latest manifestations of science
in so far as it affected the industry, but it would enable the residues
forthcoming in enormous quantities to be treated upon the spot in the
reclamation plant forming an integral part of the stockyard equipment.
The revenue derived from the disposal of the by-products rendered
available in a commercial form would not only more than offset the
charges incurred concerning transportation, but would tend towards the
primary product--the meat--being sold at a lower figure to the public.
Under the present system of local killing much of the offal escapes
reclamatory treatment for the simple reason that the quantity
forthcoming is so limited as not to be deemed worthy of exploitation,
or else is subjected to obsolete or inefficient by-product recovery
methods. In many instances it is sold to a contractor who endeavours
to conduct bulk treatment upon a reduced scale, paying a relatively
low price for the refuse and one quite disproportionate to its true
value. In some instances the contractor does not attempt to carry out
by-product recovery, but merely acts as a middleman, dispatching the
various residues to the quarters where he knows they will be taken in
hand to be worked up.
During the past few years the science of winning wealth from
slaughter-house offal of every description has made enormous strides,
effort having been concentrated upon the recovery of the very utmost
yield of by-products for the simple reason that the demand therefor
is exceedingly keen, while prices are necessarily attractive.
This applies particularly to the fats, the value of which ranges
up to as much as £50 per ton, according to grade, although other
commodities simultaneously secured, such as meal for cattle-feeding
and fertilizers, are able to command equally impressive prices. A
graphic idea of the degree to which this science has been advanced
is obvious from the dimensions, comprehensiveness and modernity of
the by-product installations which have been laid down as adjuncts to
the mammoth cattle-killing plants in various parts of the world, the
majority of which, as I have pointed out in a previous chapter, are of
British origin, design and construction, and many of which have been,
and still are being, supplied from this country. Surely it is somewhat
anomalous that other countries should come to us for the latest
expressions of ingenuity and invention in this province when we are
unable to point to a single pretentious plant in this country! At the
same time it is distinctly gratifying to learn that if Britain cannot
display sufficient imagination or commercial acumen to use plants of
this character, she certainly can build them, and is not only able to
keep well astride of the times, but is fertile in thought concerning a
highly specialized ramification of industry.
As a matter of fact it may come somewhat of a surprise to learn that
British thought is far in advance of American practise, as manifested
by the stockyards at Chicago in regard to the utilization of appliances
and process for the treatment of meat residues. The interests at the
mammoth plant were approached with the latest British development in
this line--the solvent extraction process described in a previous
chapter--it being recognized that its introduction to the American
stockyards would apply the seal of highest approval to the invention
and represent a great achievement for the British interests which had
evolved and perfected it. It possessed every virtue likely to make
appeal, more particularly the means of enabling the American packers
to add to their already huge profits. The process was investigated,
and its superiority over the methods in vogue was frankly conceded.
But the Chicago industry firmly declined to embrace the invention, not
from feelings of hostility, but because the interests concerned had
developed their own plant along lines, and to a degree which would not
readily permit a revolution. To have introduced the new idea would
have been to disorganize the whole business of by-product reclamation
and would have demanded the revision of methods, knowledge, practice,
and routine. Questions of cost did not enter into the issue at all. The
packers merely declined to disturb the system they had standardized and
had carried to such a level of perfection.
But the packers were not wholly opposed to progress. Although not
willing to introduce the system into their plants, they were quite
ready to turn over their wastes, after they had extracted as much as
they could of material value therefrom under their system, to the
British interests. The inventors accepted the proposal, and to-day one
may witness the strange and anomalous spectacle of British interests
taking over the residues from residues from the packing plants for
further treatment, and conducting the unusual method of trading to
their financial profit. It was confidence in the superiority of the new
idea which brought such signal success. Yet this exploitation of wastes
from wastes is not peculiar to Chicago. It is even being practised to a
limited degree in these islands, which suffices to prove that certain
quarters are fully cognizant of the wealth awaiting to be won from
waste, and that it pays to conduct the process to the recovery of the
uttermost retrievable ounce even from such material.
Certain of our municipalities, fully alive to the value of the waste
incidental to the operations of their abattoirs, are sparing no effort
to utilize such material to the full. However, in many instances,
their enterprise is thwarted by the circumstance that the butchers
making avail of the Corporation facilities extended, possess certain
vested interests which must be honoured. Accordingly it is not possible
to conduct reclamation to such limits as would be attainable were
methods comparable with those prevailing at the Chicago stockyards
in operation. To be able to extract the utmost from the refuse it is
imperative that the authorities should be given unrestricted control
of the animal, preferably absolute ownership. This is the reason
why the big private packing plants are able to achieve such eminent
success. They purchase the live animals, and consequently are free to
exploit them in accordance with the principles they have elaborated.
Nevertheless, despite the difficulties obtaining, much good work
is being accomplished in British circles concerning abattoir waste
exploitation.
The case of Edinburgh may be cited as an illustration. I purposely
select the Scottish city for the reason that--so far as municipalities
are concerned--it is possessed of one of the most up-to-date
installations in the country, is enterprising, and serves to bring
home how vested interests can mar a record of possible achievement by
restrictive action. The blood is sold to a contractor, who, however,
is compelled to sell back to the meat trade such quantities of this
article as may be required. A proportion of the offal is also sold by
the meat trade.
Diseased meat, condemned as unfit for human consumption, is treated by
the authorities in the Scott plant which they have acquired. The waste
is thoroughly sterilized by steam, the residuals, comprising non-edible
tallow, meat fibre and bones being sold. The plant cost £600--$3,000.
The working costs may be set down at approximately £200--$1,000--per
annum, while the income from the sale of the uncertain quantities of
meat of which disposal is made averages about £430--$2,150--per year.
The hoofs and spurs of the feet of cattle, the parings of ox-feet, a
small proportion of waste offal, and the manure originating in the
slaughter-house, are sold by the Corporation. The sum derived from
these sources during the 1917-18 financial year amounted to £533
5s.--$2,666.25--while the revenue from the sale of blood was £437
11s.--$2,187.75. All things considered it must be conceded that the
by-products resulting from the operation of the slaughter-house by
the Corporation of the Scottish city are fully utilized, although the
defects arising from divided responsibility for the development and
disposal of the wastes are obvious.
Divided interests exert another reactive influence. The public
authorities are debarred from making full avail of the latest
improvement in the art and craft of waste recovery. For instance,
although the leading abattoirs of these islands have acquired
reasonably up-to-date plants, they are all operated upon the open steam
principle, with and without vacuum. The method, while satisfactory so
far as it goes, does not offer the means of securing the utmost from
the available material. But the authorities do not feel justified
in going to the expense of acquiring the latest appliances for the
prosecution of the work of reclamation, an attitude which is perfectly
explicable in the circumstances.
Of course, the community suffers, though imperceptibly. The plants in
question allow a certain proportion of waste to be lost which in the
course of the year represents an imposing figure. Furthermore, the
whole, or the greater part, of the “stick liquor” or gelatinous liquid
thrown off during the fat reclamation process is lost, being allowed
to escape down the drains. The abandonment of the stick liquor is
regrettable because it constitutes a waste capable of being treated
with profit, as I explain later. But it is doubtful whether the average
municipal plant, even if it had absolutely unfettered control of all
the waste products arising from the slaughter of cattle for food, would
be in the position to treat the stick liquor to commercial advantage.
An evaporative plant would have to be incorporated to concentrate
the gelatinous substance to the desired density, and only in a few
instances would the quantity of material treated be adequate to render
the utilization of the stick liquor profitable. But this constitutes an
additional argument for centralized meat packing and offal exploitation
in these islands.
Accordingly effort is exclusively confined to the recovery of the
grease. I have described the outstanding features of the vacuum system
in a previous chapter, to which I would refer the reader desiring
enlightenment in connection therewith. The grease is drawn off by
a special skimming device into a fat tank to be clarified. Then it
is run into barrels or other suitable receptacles for transport. It
is scarcely necessary to point out that the grease and tallow thus
obtained from condemned meat and other offal, although thoroughly
sterilized in the rendering process, are graded only as fit for the
manufacture of soap and other articles of utility, as distinct from
products of edible importance.
The term “offal” in its application to meat residues is somewhat
ambiguous. It not only comprises material coinciding with the general
interpretation of the term, but certain portions of the animal which
are really suited to the preparation of foodstuffs for the table.
Consequently all grease recovered from the digester is not necessarily
adapted to manufacturing purposes only. In these circumstances it is
necessary to grade the fat before treatment, the fresh fat, which is
quite suitable for yielding material adapted to the preparation of
margarine, for instance, being kept distinct from the lower grades
which cannot possibly be classed as edible. Selection and separation
treatment of the two grades--edible and inedible--are profitable
because, while both are in keen demand, it is the former which is able
to command the higher market figure. But when edible fats are sought
it is preferable to employ the steam-jacketed digester because the fat
thus obtained, from the fact that the steam is not brought into contact
with the material during the cooking process, is of enhanced quality,
being sweeter, while all the natural properties of the fat are retained
for reasons already set forth.
Although, therefore, the most popular system in vogue for reclaiming
fat from slaughter-house residues is exposed to criticism, owing to
what may be described as lack of efficiency in operation due to the
recovery of the fat not being as high as it might be, it appears to
meet the conditions of the average municipal abattoir. City and borough
corporations, unlike private organizations, are not in the position
to scrap an existing plant for one which is of later date and greater
efficiency, because there is not the same incentive to reap the utmost
benefits attainable as prevails under private conditions where the
full brunt of competition is encountered. Of course, the initiative
of corporations is just as pronounced as that of private firms and
individuals, but it is the exception rather than the rule. Furthermore,
the municipality is not in the position to run a plant under full load,
or even at a uniform pressure the whole time. It is only able to handle
the waste as it accumulates during its own abattoir operations. On the
other hand, the private exploiter can acquire a plant of such capacity
as to cope with the steady flow of material from the slaughter-houses,
thereby keeping the by-product recovery installation working steadily
at a point approaching its productive limits.
Nevertheless, the results achieved with the prevailing type of plant
afford interesting reading, although it is somewhat misleading
to cite them. The material varies so widely both in quantity and
quality, while the ultimate fat-yield likewise fluctuates markedly.
A fat bullock which has been condemned would naturally be expected
to furnish a good contribution of fat. On the other hand, only a low
percentage could reasonably be anticipated from a lean cow. In these
circumstances a comparison without full details concerning the material
handled is difficult. The figures available may be set down as being
representative, though they should be accepted as being typical rather
than empirical.
A consignment of condemned meat, weighing 2,240 lb., was placed in the
digester. The quantities of the respective materials recovered were:--
Lb. Per cent.
Tallow 336 or 15
Fibrine or meat-meal 392-428 or 17¹⁄₂-20
Bone-meal 280-336 or 12¹⁄₂-15
In another instance a somewhat heavier consignment of condemned meat
was committed to the recovery plant. Its composition was:--
Lb.
Beef 84,000
Pork 1,607
Mutton 818
Veal 354
Offal 20,370
--------
Total 107,149
The tallow yield was 21,638 lb., or 20 per cent. of the total volume
passed through the digester. Pronounced quantities of the fibrine and
bone-meal were also secured. But the tallow yield alone should serve
to convince even the most sceptical that it pays to submit condemned
meat and slaughter-house refuse to a process of by-product recovery.
It was not so many years ago that such valuable waste met with an
untimely end--incineration in the destructor as the most effective and
economical means for its disposal. Had this practice been followed
in the instance under review the authorities would have allowed
material worth, according to current market quotations, at least
£500--$2,500--to vanish up the chimney in preference to the display
of a little exertion and knowledge to secure what is in such wide and
urgent request--the fat.
While the average organization, either municipal or private, conducts
operations upon too limited a scale to deal with the gelatinous or
“stick liquor,” the large establishments, on the other hand, are
confronted with such immense quantities thereof as to render its
further treatment justifiable and profitable. But the liquid is
extremely thin or weak, that is low in the gelatinous constituent in
its crude form, and so requires to be concentrated. To effect this at
the lowest cost it should be passed through the Scott multiple effect
vacuum evaporators. These are heated by the exhaust steam. In this
form of evaporator the heating effect of the steam is multiplied in
several stages, thus doing so many times more work for one supply of
fuel as compared with a simple evaporator. The evaporation proceeds
progressively and continuously, the liquor leaving the evaporator at a
high degree of concentration owing to the water having been driven off.
The gelatinous residue accruing from this treatment may be blended with
the fibrine or meat-meal, thereby enhancing the value of the latter,
which thus becomes enriched with ammonia and protein to an appreciable
degree.
For some reason or other the treatment of the “stick liquor” has
not aroused the measure of serious attention in these islands which
it deserves. While, of course, greater results are attainable from
treatment of the liquid upon a huge scale, yet relatively small
quantities can be exploited very profitably, because the jelly finds
an attractive market as crude tub size, the demand for which to-day
is somewhat keen and firm. Doubtless hesitation to turn the stick
liquor to economic account is due to lack of knowledge concerning the
improvements in the rendering process, and the difficulty encountered
in this direction in the past. Under the old system, where the
practice was to evaporate these liquors in open vessels, the nuisance
created constituted the insurmountable obstacle. The work could not be
carried out without polluting the whole neighbourhood. With the Scott
evaporator, however, no more nuisance is created in concentrating the
offensive liquor than attends the exploitation of noisome fats by
the patent digesting process, for the simple reasons that the work
is conducted in closed vessels, and all obnoxious vapours thrown off
during the treatment are led to the furnace to be consumed, escape of
the free gases into the air being rendered totally impossible.
British waste exploiters are beginning to appreciate the advantages of
the closed evaporative system, and in their determination to secure
every retrievable ounce of commercially valuable products from waste
are now devoting greater attention to the stick liquor. The policy
is one which cannot fail to pay so long as it is conducted along the
correct lines such as I have indicated.
Before leaving the question of the stick liquor it is curious to remark
how some firms, while complimenting themselves upon the assiduity
and diligence with which they treat their wastes, are yet likely
to allow a certain material, and one which is of distinct value to
their own businesses, to slip through their fingers merely from lack
of knowledge. The abandonment of the stick liquor arising from the
digestive treatment of meat-waste represents an interesting example of
such inadvertence.
Many manufacturers dealing with meat products have installed a
fat-recovery system for the treatment of their waste upon the spot,
the primary idea being to secure the good edible fat for re-use
in connection with their own processes. Furthermore, from their
association with the cooked-meat trade they find it necessary to absorb
material quantities of gelatine to carry out the glazing work in the
preparation of brawn, pies and other dainties. They purchase the crude
gelatine for the purpose, submitting it to careful treatments to adapt
it to their varying requirements. Yet, if they but knew it, they have
no need to spend a single penny--or cent--upon gelatine wherewith to
conduct the final appetizing touches to their wares. They have as much
of this raw material as they can possibly require immediately to hand
in the stick liquor, and which, in the majority of instances, they
allow to escape.
As a matter of fact this liquid residue is far preferable to the
commercial gelatine which they buy for glazing purposes. They need
only to attach an evaporator to their recovery plant to bring about
its concentration. But this is not the only advantage. The gelatine
has to be of varying densities or strengths according to its precise
application. When they have their own evaporator this desideratum
is readily fulfilled. It is only necessary to draw off the material
from the evaporators when it has reached the requisite degree of
concentration for immediate use. Not only is appreciable time saved,
but the up-to-date firms are better off in pocket because they are
utilizing a waste for which otherwise they would have to employ a
purchased commodity. Even if they conduct concentration to the
absolute it does not matter; the article is then recovered in the form
of an edible jelly. This can be clarified, if desired, to be sold as
such, or it can be sold to fellow-manufacturers who do not happen to
have such a plant. Failing such disposal there is no difficulty in
selling the jellied mass as tub size.
In a previous chapter I have described the reclamation process
practised by the military authorities in connection with bones
arising from the cutting-up of meat for the army, as well as those
recovered from the swill-tubs. As indicated, however, exploitation is
conducted only to a certain point, when the bones are handed over to
the degreasers. It is then that the true recovery of the commercial
constituents of the bone commences. The bone is an invaluable friend
to the human race as an article of commerce, though it is to be feared
that what may be described as the “bone tree” is only imperfectly
understood. Its far-reaching value as a fertilizer is certainly
appreciated, but this really represents the final application of the
article, and may be said to be the only remaining field of utility for
the ultimate residue of a residue. Bones enter into a wide range of
industrial and manufacturing operations. For this reason they should be
carefully gathered and retained for surrender to recognized collecting
mediums rather than suffer abandonment or destruction.
The housewife is prone to regard them as mere waste when she has
extracted the utmost recoverable value therefrom in the kitchen.
She may possibly retain them until the itinerant specialist in this
commodity, to wit, the rag-and-bone man, comes round, in which event it
is sure to be sped once more on a journey of industrial exploitation.
But at least one-third of the bones which enter the households of
Britain escape reclamation. They are wantonly wasted, and it is to be
feared that the kitchen stove is mainly responsible for this loss. The
volume of bones which should be forthcoming from domestic circles in
Great Britain, were the dictates of thrift religiously followed, is
scarcely appreciated, but it is estimated that the supply should be at
least 100 tons per week from every million members of the population.
In these islands the bones are divided into two broad classes. The one
division, comprising what is known as “green” (raw) bones, represents
those collected from butchers’ shops, bacon-cutting works, and other
similar sources. The second class, defined as “streeters,” include
those forthcoming from the recognized collectors of such waste, hotels,
restaurants, clubs, and private houses, and are those which have been
passed through one or more cooking processes.
In the case of green bones it is customary to digest them, when really
fresh, with open steam to recover the edible fat. Shank and marrow
bones, as distinct from rough bones, are also able to yield a certain
proportion of edible fat, and after having been digested or boiled
still retain a considerable percentage of grease which it pays to
extract. Consequently these, together with a certain quantity of less
fresh green bones, and the streeters, are then passed through the
benzine extractor to be degreased down to 1 per cent.
The shank and marrow bones are sawn up, the centre sections being
selected for the production of such useful articles as knife and fork
handles, buttons, and other utilitarian commodities for which their
composition renders them eminently suitable. The ends or knuckles are
degreased by submission to the solvent extraction process, and then,
in some works, are subjected to further chemical treatment, which is
somewhat elaborate, to be converted into baking-powder.
Otherwise the bones, after being degreased, are passed through other
processes for the extraction of their gelatinous constituent. This
is secured in the form of a liquor which is evaporated in vacuo to a
jelly. The last-named is cooled into cakes and then dried on nets,
or, if preferred, the liquor may be dried direct into glue-powder. By
following a more complicated process gelatine can also be prepared from
the degreased bones. But the gelatine thus obtained does not compare in
quality with that extracted from skins. The degelatinizing process is
not always followed, for the reason that some makers prefer to produce
the higher quality bone-meal which is procurable from non-degelatinized
bone. Obviously, however, the more profitable and economic procedure is
to pass the bones through an associated glue plant.
The ultimate residue, whether degelatinised or not, is a bone-meal
which constitutes the well-known fertilizer. The bone-meal, to be of
the utmost feeding value to the soil, should carry little or no fat.
At the same time, however, it should be rich in ammonia and phosphoric
acid or superphosphate, which is determined in terms of tribasic
phosphate of lime. To show how these requirements can be adequately
fulfilled by submitting the raw waste to a complete recovery process,
such as I have described, an analysis of a typical bone-meal produced
from degreased bones--degreased by the benzine extraction process--but
which have not been degelatinized, is given thus:--
Per cent.
Tribasic phosphate of lime 46·60
Nitrogen, 6·07 per cent. = ammonia 7·37
Moisture 8·04
Fat 1
The high percentage of ammonia, namely 7·37 per cent., deserves
especial notice inasmuch as it compares with a yield of 4·5 per cent.,
which is the average figure recorded with fertilizing meal obtained
from steamed bones. It may possibly come as a surprise to many to learn
that it is the proportion of the nitrogenous content, as represented
by the ammonia, rather than the phosphoric acid content, which really
determines the commercial value of this manure. The higher the figure
to which the ammonia figure can be forced the more attractive the price
which the fertilizer will command upon the market. Thus, under normal
conditions, every 1 per cent. rise in the ammonia constituent will
increase the price of the bone-meal by 14s.--$3.50. On the other hand,
a 1 per cent. increase in the proportion of superphosphate only serves
to increase the price of the meal by 11d. to 1s. 2d.--22 to 28 cents.
The grease obtainable from green bones varies somewhat. It is affected
to a marked degree by the skill and care with which the butcher wields
his knife. If the bone should be scraped very clean and carefully,
naturally the bulk of the attached fat is removed. But an average
collection of green bones will yield about 15 per cent., or 360 lb.,
of fat per ton of bones treated, while the dry bone-meal will range
from 1,286 to 1,344 lb. Bones which have been collected from marine
store dealers and rag-and-bone merchants are not so liberal in fat
yield. The repeated cooking to which they have been subjected in
connection with the preparation of dishes for the table relieves them
of approximately 5 per cent. of the fat which they originally carried,
i.e. in the raw condition. Consequently, degreasing only enables about
10 per cent., or 250 lb., of fat to be recovered from every ton of
bones treated. In this instance the bone-meal yield may be set down at
1,568 to 1,680 lb. per ton of bones. The grease remaining in the meal
varies from 0·5 to 1 per cent.
As may logically be supposed, cattle-slaughtering for food produces
large quantities of blood. This is an extremely valuable residue, and
so is carefully collected in suitable vessels. It is then transferred
to shallow receptacles and permitted to stand for a time. Blood is
composed of two fundamental constituents--the serum and the clot
respectively. The former, which is the albumen, is the glutinous-like,
yellowish liquid which comes to the surface, the clot settling to
form as it were a sediment. The serum is recovered by skimming with a
suitable device, to be distributed in extremely thin layers, applied
with a brush, to dry. Such a careful procedure is imperative owing to
the difficulty of drying out albumen. When dry the blood-albumen is
peeled in the form of thin flakes. Its applications are numerous, one
of the most important being its employment for the clarification of
sugar. The clot is likewise secured to be sent to the special plant,
where it is also dried.
It is common knowledge that blood constitutes a magnificent fertilizer,
and this is the purpose to which the dried clot is applied. In a
well-designed vacuum drying plant, such as the Scott, which has been
designed especially to treat such residue, the efficiency is high. The
yield from the clot may be said to range from 25 to 30 per cent.--560
to 672 lb.--per ton of raw clot treated, and is recovered in the form
of a rich red dry powder.
One great objection levelled against the recovery of the blood for
fertilizing purposes has been the very offensive odour which is thrown
off during the drying operation. But when the task is conducted under
the vacuum system no such nuisance is created, because the obnoxious
gases are led to the fire to suffer combustion. In dryers of the
conventional type, in which the noxious gases are removed by the
aid of an exhausting fan, or suffer discharge into the chimney, the
process does represent an intolerable nuisance to the neighbourhood,
because there is nothing to prevent the pollution of the atmosphere.
Furthermore, and this is the most important point to remember, by
drying the blood under the vacuum system the ammonia content of the
waste, which normally is high, can be preserved to the full, owing to
the drying operation being carried out at a much lower temperature than
is incidental to the usual practice.
Dried blood appeals to the farmer for the nourishment of his land
essentially because of its pronounced proportion of nitrogen or
ammonia. Consequently it is incumbent to keep this figure as high as
possible and thus secure the advantages of market quotation. Naturally
the percentage thereof in the resultant meal will vary strikingly
according to the drying process practised. Ammonia is an exceedingly
volatile ingredient, its tendency to escape being accentuated as the
temperature employed is increased. It is only by keeping the heat
factor at a low level consistent with the complete fulfilment of the
desired operation, that the ammonia can be retained. Under the vacuum
system this end is assured, owing to the low boiling-point due to the
reduced pressure or vacuum. A typical analysis of vacuum-dried clot
blood may be cited:--
Per cent.
Moisture 9
Mineral matter 1·61
Nitrogen 14·02
⤷
= ammonia 17·02
In cases where the albumen is not required separately the whole blood
is dried without being separated or “clotted.”
It is obvious from what I have related, that the recovery of
by-products from what has always been regarded as waste of a most
repulsive character, that is from the popular point of view, can be
turned to striking commercial and industrial account. Similarly it
is only too apparent that such by-product reclamation as is possible
demands a plant of the most complete description, to ensure all and
every substance of utilitarian value being secured along the most
efficient lines and to the uttermost ounce.
The day has gone when the crude methods which sufficed to satisfy
individual or specific requirements should be continued. To endeavour
to render it profitable to recover but one article out of many which
are reclaimable simultaneously, and for the expenditure of only a
little more effort, time and money, may be compared with mining for one
hundred carat diamonds and allowing all those of lesser weight to fall
back into the earth.