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A. For most of human history, keeping food fresh was a constant problem. Meat, fish and milk spoiled within days, and fruit and vegetables could only be eaten in season. People therefore relied on traditional methods of preservation. For example, they dried fish in the sun, salted pork, smoked meat over fires and pickled vegetables in vinegar. Salt, in particular, was so valuable that it was traded over long distances. These techniques worked, but they also changed the taste and texture of food. In addition, they could not keep products truly fresh. As a result, most people ate food that was grown or raised close to where they lived.

B. Cold has long been known to slow down decay. In many parts of the world, wealthy families built ice houses, which were deep pits or thick-walled buildings used to store winter ice. In the nineteenth century, this idea became a large business. Workers cut blocks of ice from frozen lakes and rivers in cold regions and packed them in sawdust. Ships then carried the ice to warmer places, including the Caribbean and even India. However, natural ice was expensive to transport, and a large part of each cargo melted on the way. Moreover, a mild winter could mean a poor harvest of ice and high prices the following summer.

C. The solution was to produce cold artificially. Scientists had observed that when a liquid evaporates, it absorbs heat from its surroundings. Engineers used this principle to design machines that compressed a gas, allowed it to turn into a liquid, and then let it expand again. Each cycle removed heat from an enclosed space. By the second half of the nineteenth century, several inventors had built working machines, and some were used to make ice in factories. At first, the equipment was large, noisy and costly. It was mainly found in breweries, which needed steady cool temperatures to produce beer all year round. Later, smaller and more reliable designs made the technology suitable for many other industries.

D. One of the most important early uses of refrigeration was at sea. In the late 1870s and early 1880s, ships fitted with freezing equipment began to carry meat across the oceans. Countries such as Argentina, Australia and New Zealand had huge numbers of cattle and sheep but relatively small populations. Britain, on the other hand, had a growing urban population that needed cheap meat. Frozen cargoes could now survive voyages of several weeks and arrive in good condition. This trade quickly expanded, and it changed farming in the exporting countries, where large areas of land were turned over to livestock for overseas markets.

E. On land, refrigerated railway wagons had a similar effect. These wagons were first cooled with ice, and later with mechanical systems. In the United States, they allowed meat to be processed in a few large central cities and then sent to distant markets. Before this, animals were often transported alive and slaughtered near the customers who would eat them. This change created a much larger and more competitive meat industry. Refrigerated transport also helped farmers in warm regions. For instance, growers of oranges and other fruit could now send their harvests to cities thousands of kilometres away. Consequently, regions began to specialise in particular crops rather than producing a little of everything.

F. Refrigeration then entered the home. Early household refrigerators appeared in the 1910s and 1920s, but they were too expensive for most families. Some of them also used dangerous gases, such as ammonia and sulphur dioxide, which could cause injury if the machine leaked. In the 1930s, new chemicals called chlorofluorocarbons, or CFCs, were introduced because they were not toxic or flammable. Prices fell, and after the Second World War the refrigerator became a standard kitchen appliance in many wealthy countries. Families could now shop once a week instead of every day, and frozen foods became popular. In addition, people could keep leftovers safely for longer.

G. The development of the modern cold chain completed this transformation. A cold chain is a connected series of refrigerated stages, from farm or factory to warehouse, transport, shop and, finally, the home. Today, refrigerated shipping containers carry fruit, fish, flowers and medicines around the world. Because of this system, shoppers in northern countries can buy fresh grapes in winter, and seafood caught in one ocean can be sold on another continent. In addition, refrigerated storage allows producers to hold goods until prices are better. Supermarkets depend heavily on the cold chain, and it has made the diets of many people far more varied than those of their grandparents.

H. Nevertheless, refrigeration has also created problems. In the 1970s, scientists found that CFCs were damaging the ozone layer, which protects the Earth from harmful radiation. An international agreement signed in 1987 led to these chemicals being phased out. Furthermore, refrigeration uses a large amount of electricity, and some replacement gases contribute to global warming. Access is also unequal. In many lower-income regions, the cold chain is incomplete, so a significant share of harvested food spoils before it reaches consumers. Improving cold storage in these areas could therefore reduce waste and increase food supply, provided that cleaner and more efficient technologies are used.

The development of refrigeration and its impact on global food distribution

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