Food from the Farthest Corners of the Earth
Ninety-eight days it took, right round the Horn, and sparks from the funnel set fire, more than once, to the sails. A strange craft this, its funnel belching smoke, yet sails stretched tight and bulging up the three slender clipper masts. The steam-engine had come to stay, it was being used increasingly for the propulsion of river and coastal craft, but the smoke and steam from the pride of the Albion Line, soon to be the Shaw Savill Line, the clipper ship, Dunedin, served a different purpose altogether. It was initiating a revolution in shipping and at the same time, a revolution in the economy of those countries the shipping served. For this sleek vessel of thirteen hundred tons was the first on the all-important New Zealand run to be fitted with the new Bell-Coleman refrigerating machine. It was this ungainly, yet remarkably efficient apparatus, still in its teething stage, which required a funnel and steam to operate it, while the ship moved serenely on, driven only by sail.
Ninety-eight days from that morning in February 1882, when she left her New Zealand dock, the Dunedin docked at London. The news had preceded her, and as soon as the unfamiliar silhouette was sighted coming up the Thames, a crowd ran on ahead to watch this incredible cargo unloaded. For in her holds the Dunedin held five thousand frozen carcasses of lamb.
Surely, men said, it would be, if not completely rotten, at least so poorly flavored after its long confinement that only a beggar off the street would deign to try it?
They were wrong. The meat was as fresh as the day it had been slaughtered. One only of the carcasses was damaged, had to be condemned; the rest were plump, fresh, succulent, and they sold rapidly, for sixpence halfpenny a pound, of which twopence three-farthings was the cost of freighting from New Zealand (a freight charge which has hardly altered, though the price of meat has soared). The price brought a respectable profit to the New Zealand farmer, a profit which could and would be multiplied as the new refrigerating vessels were made ready.
A new industry had been born. The refrigerating ships would not only bring great prosperity to New Zealand, and first-class meat at a reasonable price to England, but they would solve a major problem, that of disposing of the sheep. For they bred rapidly and there were not enough mouths in all the southern colonies to eat them. Sheep were being slaughtered, their carcasses flung into the sea, to get them out of the way. Apart from shipping them alive to Britain, which was absurd, there was little that could be done with them, when their fleece had been shorn.
But refrigeration changed all that. Meat could be frozen immediately after slaughter, loaded onboard a suitably equipped vessel, and kept at a temperature below freezing point till it was unloaded in England. There was no decay, no loss of flavor.
The discovery completely altered New Zealand’s economy, gave a prosperity which few could have dreamed of, which has been maintained to this day, since that first trip in 1882. Today, there are twenty sheep in New Zealand for each citizen, but to-day there is no question of hurling them into the sea; they are frozen and shipped all over the world.
The Bell-Coleman refrigerator was not the first to be invented, and the Dunedin was not quite the first ship to be fitted with one, but because of the enormous length of journey, the huge part refrigerator ships were to play in the economy of New Zealand, this first voyage was a development of great significance.
The principle, of keeping food fresh in a low temperature, is old indeed. For centuries men had hacked blocks of natural ice from the frozen surface of ponds and rivers, had kept it as long as possible in shady, sheltered places, using it, piece by piece, to keep their food fresh. Parts of the world where natural ice was unknown locally could still get shipments of it from colder climates, and a regular trade built up, shipping ice from Massachusetts to the West Indies. Obviously, a great deal of the ice melted en route, and that which survived the journey was awkward and unpleasant to handle; it was far from an ideal method of cooling.
For tropical climes, out of reach of ship-borne natural ice, men could achieve some cooling of water by storing it in porous earthenware vessels. The water seeped out gradually and evaporated from the outside of the container, and this evaporation reduced the temperature of the water remaining. It was this method of cooling, thousands of years old, which pointed the way to our modern mechanical systems, which rely on exactly this principle. They have been extensively developed, and now mechanical refrigeration has opened up undreamed-of fields, is used in a hundred differenl ways which have nothing whatever to do with food, from the shrinking of rivets by extreme cold so that they can be hammered in and allowed to expand to form an absolutely permanent bond, to the preservation of old books and paintings, and the slowing down of the human mechanism for surgery.
There are several claimants for the honour of having produced the first workable refrigerator, but the fruits of their labours have, for the most part, been lost, and we must date effective refrigeration from the patenting, in 1834, of a machine by Jacob Perkins. He was an American of an inquiring turn of mind and he experimented with much during an energetic lifetime, from the printing of postage stamps to the manufacture of high-pressure boilers. Somewhere along the line he decided to invent his own cooling device; by this time, having wearied, it seems, of his small home town of Newbury-port, he had travelled as far as England, and here, in London, the first refrigerating machine was patented.
Others were experimenting with a principle which, as we have seen, dates back to man’s earliest days under a tropical sun, and many variations were tried. Instead of water oozing through a porous pot, man experimented with the behaviour of all sorts of substances, from ether (chosen by Perkins) to ammonia and compressed air. All processes depended, still do, on using a substance which would easily change from liquid to vapour. Water, of course, does this, but at a temperature too high to be of much use for real cooling. In fact, there is no natural liquid which vaporizes at a temperature suitable for refrigeration; the liquid has to be manufactured, in the refrigerator itself, by compressing a gas, then cooling it, until it liquefies. If this liquid is then permitted to expand once more and become vapour, it will extract heat from its surroundings just like the porous pot.
With Perkins’s system, still typical, the ether vapour is compressed by a pump, driven by a motor, and thus becomes liquid. (This preliminary stage gives off heat, and the heat must be disposed of, outside the area to be cooled: in domestic refrigerators it escapes into the air surrounding the machine.) The liquid now passes to an “expansion valve” which allows it to escape into a larger chamber. Its pressure drops suddenly; it vaporizes, and in the process takes a great deal of heat from its surroundings. In refrigerating systems this suddenly chilled gas passes, in pipes, through the space being cooled, or, sometimes, is used to chill a liquid like brine which is then more conveniently piped wherever its cooling effect is needed.
There are many versions of this compression refrigerator, using different “refrigerant” gases, and they all involve some mechanical method of squeezing the gas to make it into a liquid; then, having allowed this liquid, which grew warm on compression, to settle back to normal temperature, they let it escape to a larger chamber, whereupon it becomes a gas, and extremely cold. After it has circulated through pipes, done its job of cooling, it is recompressed. The process repeats itself. In a typical example, ammonia in its liquid state at a temperature of 82 degrees Fahrenheit is allowed to expand; immediately it drops in temperature to 6 degrees Fahrenheit. Anything in the vicinity of the chamber in which this takes place, or the pipes which lead the vapour back to the compressor, will, obviously, become very cold.
The same principle, but without using mechanical compression, is employed in the so-called “absorption” system of refrigeration. In this, ammonia gas, which absorbs easily into water (at 55 degrees Fahrenheit water will absorb a thousand times its volume of ammonia vapour), is released in large quantities when that water is heated by a small gas flame or electric element. Once released this way, into a closed chamber, it soon builds up almost as high a pressure as is done mechanically with a compressor. It is then, as in the compression system, released into a larger chamber through an expansion valve and becomes very cold.
The absorption system, though less efficient, has the advantage, because there are no moving parts, of being entirely silent, whereas the electric compressor in even the most modern refrigerator is audible. (And the steam-engined compressors on the Dunedin could only have been deafening. Apart from this, their somewhat erratic behaviour caused the gallant captain, in an effort to rectify some puzzling fault, to freeze almost solid in a ventilator, whence he was hauled with a rope round the ankle, but he made a swift recovery.)
The science of refrigeration has made great strides since the Second World War, in four distinct but equally important lines: industrial refrigeration, medical refrigeration, domestic refrigeration and air-conditioning. The industrial uses include not only the pre-shrinking of bolts and rivets, but the de-humidifying of air for blast furnaces, the setting of concrete, the hardening of mud in mining, so it can be easily excavated, the cooling of surfaces of high-speed aircraft and missiles, and of course the common task of making ice rinks. In medicine, an artificial hibernation of the body can be induced by lowering its temperature. This “hypothermia” reduces the body’s need for oxygen, so that a surgeon can cut off the blood’s circulation long enough to operate on the heart or the brain. Normally, three minutes without blood-borne oxygen damages the brain irreversibly, but under hypothermia it can dispense with all oxygen for up to twelve minutes, long enough for some brain operations.
We are all familiar with domestic refrigerators, called, unbeautifully, “fridges” in England and, nostalgically, “iceboxes” in America, the remarkable gadgets by which so many households, for a small expenditure on electricity or gas, keep food cool and fresh, make their own supplies of ice. At the same time, domestic air-conditioning is being developed, so that, soon, any household that wishes it will be able very cheaply to purchase an apparatus to keep the air inside the house as cool in summer and as warm in winter as desired, while at the same time filtering and cleaning it, so that the open casement, for all but window-boxes and eloping lovers, could become a thing of the past. On a larger scale, the industrial air-conditioner has made office and factory work enjoyable in climates where it was all but impossible.
We must not forget the rapidly expanding frozen-food industry, which now lets us buy, already frozen, many different varieties of food which may be out of season or otherwise unobtainable. Vegetables and fish can be quick-frozen in times of glut, to be consumed in times of scarcity. Whole meals, pre-cooked, can be frozen, to be consumed after only a little warming, as tasty and attractive as when they were prepared by a skilled chef, a week, a month, or a year ago.
Side by side with the development of refrigeration techniques has come the study of materials which insulate the cold space from its surroundings, for there is little use in trying to cool a box or a room or a body or a lamb chop, if heat floods back into it from outside. In the early days of shipping natural ice round the world, pine sawdust was well regarded as an insulator to be spread between the blocks; nowadays corkboard is extensively used for lining, say, the doors of refrigerators, but a whole new range of man-made substances like glass wool, polystyrene and the other plastics is coming into use. Their insulating capacities are so great that, in theory, at least, a house could be set at its correct temperature in early autumn and left that way throughout the winter, with the minimum of heating, assuming, of course, that no one was foolish enough to open the door.
And although he must have had some inkling of what his brainchild held in store for the world, one wonders if Jacob Perkins, back in 1834, could have guessed a tenth part of its possibilities?
- Green Cooling Initiative on alternative natural refrigerants cooling technologies
- “The Refrigeration Cycle”, from HowStuffWorks
- “The Refrigeration”, from frigokey
- American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
- International Institute of Refrigeration (IIR)
- British Institute of Refrigeration
- Scroll down to “Continuous-Cycle Absorption System”
- US Department of Energy: Technology Basics of Absorption Cycles
- Institute of Refrigeration