Thermal cooking

A thermal cooker is a cooking device that uses thermal insulation to retain heat and cook food without the continuous use of fuel or other heat source. It is a modern implementation of a haybox, which uses hay or straw to insulate a cooking pot.

History

The earliest dates from Medieval times. After heating over a fire, a hot, earthenware pot containing food was placed in another, larger pot, box or hole in the ground, insulated by hay, moss, dry leaves or other material, and covered. The heat conserved within would slowly cook the food inside, saving fuel and work. An example of this type of cooker was found in Wales by a Monmouth Archaeological Society excavation.

Medieval instructions for cooking without fire taken from an Anglo-Norman manuscript in the British Library:

Modern thermal cookers

In the mid 1990s steel thermal cookers were developed in Asia, consisting of two stainless steel pots, one within the other. The inner pot is used to bring the food to the boil and the insulated outer pot is used as the container to retain heat and continue the cooking process. Some use insulation material between the outer pot walls, while others use a vacuum.

Vacuum flask

A vacuum flask (also known as a Dewar flask, Dewar bottle or Thermos) is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck. The gap between the two flasks is partially evacuated of air, creating a near-vacuum which significantly reduces heat transfer by conduction or convection.

Vacuum flasks are used domestically to keep beverages hot or cold for extended periods of time and for many purposes in industry.

History

The vacuum flask was designed and invented by Scottish scientist Sir James Dewar in 1892 as a result of his research in the field of cryogenics and is sometimes called a Dewar flask in his honour. While performing experiments in determining the specific heat of the element of palladium, Dewar formed a brass chamber that he enclosed in another chamber to keep the palladium at its desired temperature. He evacuated the air between the two chambers creating a partial vacuum to keep the temperature of the contents stable. Through the need for this insulated container, James Dewar created the vacuum flask which became a significant tool for chemical experiments but also became a common household item. The flask was later developed using new materials such as glass and aluminum; however, Dewar refused to patent his invention.