An oven is a chamber for heating, baking, drying, or hardening a substance. In addition to the familiar ovens for baking bread or cake or for roasting, ovens for industrial purposes are in universal use. Many products of modern industry contain at least one part that has passed through an oven during manufacture.
Ovens for Cooking
Primitive peoples generally bake or roast by covering food with hot ashes, earth or heated rocks. Archaeologists have discovered in the caves of the Swiss lake region the calcined remains of bread made from coarse grain, and have surmised that the Stone Age bakers placed their loaves on hot rocks and covered them with ashes. Even today the Polynesians prepare a tasty and elaborate dish in hot earth. Such crude roasting represents an advance over the most primitive cooking of any kind, which consists of direct broiling on a stick or grid of sticks.
In Egypt the simplest and earliest form of oven consisted of two or three vertical stones supporting flat stones. By about 2500 B.C. the Egyptians used brick furnaces in the kitchens of the larger estates, and by about 2000 B.C. they had devised a clay oven with a grate. In Mesopotamia, the temple kitchens of Ur had large clay beehive bread ovens and clay cooking ranges with flat tops and circular flues. Terra-cotta models surviving from early Greece seem to indicate that women baked bread by building a clay oven like a huge bowl, burning grass and sticks inside and around it, and after the fire died down placing flat loaves inside it. Remains from Roman civilization and the late Middle Ages indicate the use of ovens like those still in use on the Gaspe Peninsula and in other parts of the world that have retained a semipeasant economy. These ovens consist of a simple masonry chamber above a firebox.
Baking in colonial America was done in alcoves built into the masonry backs of the wide kitchen fireplaces, or in completely enclosed Dutch ovens. In the cities, the bakers often put their ovens underground, probably to maintain heat more effectively. In the early 1700's the New York City Common Council granted a number of permits for building such ovens under the road before the bakery.
In the latter part of the 18th century, metal ovens and kitchen ranges appeared both in England and the United States. The first metal ovens were tin boxes for use in fireplaces. The first kitchen ranges containing ovens were undoubtedly influenced by the "Salisbury Kitchen" and other galley stoves for ships, which were preferred because they could be used for baking, roasting, and boiling at the same time.
No basic changes in ovens were made until the 1890's, when gas became popular for cooking. In the 1930's electric ovens with thermostats and automatic timers were introduced. These could be turned on and off automatically at a predetermined time selected by the user. Another advance was the self-cleaning oven, available in both gas and electric models. In these ovens, temperatures of 870° to 960°F (460°-510°C) reduce the soil to a fine ash. A radical departure in oven design came with the microwave oven, developed in the 1950's, which came into wide home use in the 1970's. Heating foods internally by radiation, these ovens cook material in much less time than is required by conventional ovens. A potato, for example, may be cooked in four minutes.
However, the U.S. government warned of possible radiation hazards to users unless the door was tightly closed and in good working order.
Ovens in Industry
The evolution of industrial ovens parallels that of cooking ovens in that the substance to be heated was at first simply covered with earth or ashes for maintaining heat while quenching flames. When a permanent vault was constructed for making charcoal or coke instead of shoveling earth on burning wood or coal, the beehive oven appeared. Johann Rudolf Glauber, the German chemist, described the making of wood tar in a beehive oven in his book Miraculum Mundi Continuati in 1657. But it did not come into general use until the 19th century. This type of oven was an important instrument of the Industrial Revolution, since for many years it supplied the steel and iron industry with coke, cities with illuminating gas, and many industries and trades with other byproducts.
Kilns for ceramics and refractories for glass-making, along with all sorts of ovens for baking paints and varnishes and making plastics- all descend historically from the simple chamber of masonry over a fire. Baking, drying, tempering, annealing, impregnating, aging, melting, preheating merely suggest the variety of ways in which industry uses ovens.
Like the oven for cooking, industrial ovens have become more efficient because the use of gas and electricity has led to more automation. Many industrial ovens are now equipped not only with controls of temperature and time, but also with automatic devices for putting the product into the oven and taking it out again.
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