is an example of preserving food by sealing. Its history is inseparable from that of bottling; so the two are treated together here. Each involves heating food to sterilize it and sealing it in an airtight container. However, the use of metal containers (cans) soon became dominant in the canning industry, while bottling in glass containers was the usual practice in domestic kitchens (although it has continued to be used in the food industry for specialized or expensive or visually attractive items (e.g. fruit in syrup)).
The theoretical basis of canning was not established until 1861, when the French scientist Louis Pasteur showed that micro-organisms were the principal causes of food spoilage. But empirical knowledge had pointed the way from early times. As explained under sealing, the medieval raised pie was a confection which could serve as a preserving container; and the old practice of potting certain foods must have produced at least a vague realization that cooking plus excluding air made food keep. In 1680 such notions were given concrete form by the anonymous author of A Book of Receipts According to the Newest Method, who wrote:
To keep Gooseberries, Damsons, or Bullies [bullaces]. Gather Gooseberries at their full Growth, but not ripe, Top and Tail them, and put them into Glass Bottles, put Corks on them but not too close, then set them on a gentle Fire, in a Kettle of cold Water up to the Neck, but wet not the Cork, let them stand till they turn White, or begin to Crack, and set them till cold, then beat in the Corks hard, and Pitch them over. You may also do them in an Oven if you please, or cork them down hard, and pitch them over, and they will keep without scalding.
This recipe seems to have had no influence, perhaps because of the misguided advice at the end, which may have tempted people to try the invalid alternative technique ‘without scalding’. Otherwise, subject to some minor problems, the recipe should have worked.
The decisive step forward into the era of successful bottling and canning of foods was not taken until the beginning of the 19th century, when the Frenchman Nicolas Appert perfected a method of bottling which won the approval of the French government and was described in his book L'Art de conserver (1810). An English translation appeared in 1811, and an American edition in 1812.
Appert's technique was as follows. Food of any type—meats, soups, fruits, and vegetables—was placed in a stout wide-mouthed jar, and this was closed with a stopper composed of several layers of cork with the grain running crossways to reduce porosity. The stopper was sealed with an odd but effective mixture of cheese and lime, and wired down as for champagne. The jars, enclosed in sacking in anticipation of some bursts, were then heated in a water bath. Appert worked out cooking times for each type of food. All his mixtures were either liquid themselves or packed in liquid. Tests carried out from 1806, including the shipment of jars across the equator, vindicated the technique.
Parallel work was taking place in England. In 1808 Bryan Donkin was awarded five guineas for a method of bottling fruit, which he had borrowed without acknowledgement from Appert. His corks were kept moist, and thus airtight, by storing the jars on their sides in the manner of wine. Not long afterwards he introduced the use of tinned iron containers in place of glass jars—hardly surprising, as he was a partner in an ironworks. This idea had already been patented twice in Britain, in 1810; it is not clear whether Donkin was aware of this. In any event there was no legal challenge when he began to manufacture canned foods in 1812. He offered samples to the Royal Navy and to several explorers, and the firm of Donkin, Hall & Gamble became an established naval supplier from 1818.
Two cans made for an Arctic expedition of 1824, one of veal and one of carrots, survived unopened and were investigated 114 years later. The contents were in sound condition, only slightly spoiled by the slow chemical attack of the tin coating; they could have been eaten safely, but the investigators did not dare try.
These early cans were bulk containers, holding 1 or 2 kg (2–4 lb). The metal was thick and the seams were hand soldered; the cans had to be opened with a hammer and chisel. They were not completely closed before heating, as Appert's jars had been; a small hole was left for the escape of steam. This was quickly soldered when the contents boiled, and heating was continued for the full processing time. To verify that all cans had been properly sealed, and that no air had been drawn in when the can cooled and pressure inside fell, the cans were left in a warm place for a month. Any faulty can would bulge, as a result of gas being formed inside from the spoilage of the food.
In the late 1840s, when still larger cans were being made—net weight over 6 kg (14 lb)—a scandal was caused by the discovery that many such cans of meat went bad. It can now be seen that this was because the distance from the outside of the can to the middle was so great that heat did not have time to diffuse right through the solid block of meat, and the centre did not reach boiling point. Cans with liquid or partly liquid contents did not suffer from the problem, however large they were, because convection currents could carry heat around inside them. Admiralty investigators, although not understanding this, wisely recommended that no cans should have a capacity of more than 2.7 kg (6 lb), and that the navy should have its own cannery, which was established in 1856 at Deptford.
This was still several years before Pasteur's discovery, and long before the great resistance to heat of certain spore-forming bacteria had been discovered. Nevertheless, there was a feeling that greater heat was desirable, and experiments were made to raise the boiling point of the water bath (with salt, which unfortunately corroded the outside of the cans) and by pressure cooking. Autoclaves (large pressure cookers) were, however, feared because they sometimes exploded, and it was not until the end of the century that they came into general use.
The earliest canned foods had been expensive items, whose use was only warranted for special situations—ships at sea for long periods, Arctic explorations. But meat was scarce and dearer than usual in Britain in the 1860s, and it became economically feasible to import canned mutton and beef from Australia. In the 1870s the USA entered the British market, followed later by S. American countries. The canned meat thus imported was cheap food for the poor. It was widely disliked for its coarse, fatty nature, as shown by some of the nicknames it acquired. The Royal Navy called theirs ‘Sweet Fanny Adams’, after the victim of a notorious murder in 1867, whose victim was hacked into small pieces. This tradition proved to be durable. During the Second World War the cans of meat supplied to Axis troops were labelled ‘AM’. The Germans called it ‘Alter Mann’ (old man), and the Italians ‘Asino morte’ (dead donkey).
Canned fruits and vegetables were at first only prepared for the luxury trade or special purposes, but evolved into an inexpensive item for the mass market. Canning of tomatoes on a large scale began in Pennsylvania in 1847–9, at a time when this fruit had not yet won acceptance in the English-speaking world. A lively marketing campaign by the canner, who sent samples to President Polk and Queen Victoria, overcame doubts, and it was largely due to this campaign for the canned product that tomatoes came to be a common and popular food. By the 1880s large quantities of canned tomatoes were being sent to Britain from the USA. Peas, first canned on a large scale in Baltimore in the 1850s, had also progressed down market from luxury to staple. Californian peaches were widely sold in cans from the 1860s, but canned pineapple, from Hawaii, did not appear until 1892.
Cans of pork and beans were made for the fishing fleet, in Portland, Maine, in 1875; and these may be regarded as the parents of the cans of ‘baked beans’.
The first canned fish were sardines, which were commercially canned at Nantes as early as the 1820s. Sardines spoil quickly and, unless they are to be eaten on the spot, always need preserving in some way. Traditionally they had been salted and sometimes smoked. Canning in oil gave a product more like the fresh fish, and which was esteemed as a delicacy.
Another familiar canned product is condensed milk. Appert himself had bottled condensed milk for the French government trials, and others continued to make it thereafter, sometimes sweetening it. The object was not only to preserve milk (‘fresh’ milk sold in towns in the early 19th century was often sour and contaminated) but also to reduce its inconvenient bulk. The breakthrough that made condensed milk popular was achieved by Gail Borden of Brooklyn, New York, who in 1856 patented a vacuum evaporation process which worked at temperatures below boiling point and resulted in a less obviously ‘cooked’ taste. Borden's condensed milk was sweetened, but unsweetened evaporated milk followed. (The sugar has a preservative function, and unsweetened milk has to be treated at a higher temperature.)
By the 1880s canned foods had an important place in popular diet. Cans looked much like those of the 20th century, and the metal was thin enough to permit opening with a can opener. Sealing, however, was still done by a cumbersome soldering process.
Modern methods require, for most foods, an initial blanching at a temperature slightly below boiling point. This destroys enzymes that might discolour the food or give it an off flavour, and also removes air, which helps when filling the can.
Filling is done on a continuous production line. The can is packed with food and topped up with brine, sauce, or syrup as appropriate, leaving a head space of 6 mm (0.25 ″) to allow for expansion. Then the lid is clamped on by a machine which produces a double seam. It is important that the contents are hot when this is done, so that when the can is heated later it will not burst. If necessary the can may be warmed with hot water or steam.
The can is then heated in an autoclave, which allows the contents to be heated well above boiling point. The high pressure outside the can also keeps it from bursting. The cooking temperature varies with the acidity of the food. The bacteria which cause botulism cannot grow in acid conditions, so acid foods such as canned fruit and tomatoes need be heated only just enough to bring the centre of the can to boiling point. Other foods have to be heated to 121 °C (250 °F) or more for at least three minutes to destroy the spores of this dangerous organism—which is why canned vegetables often seem ‘overcooked’.
Ralph Hancock is an encyclopedist with a special interest in food history and food science.
