A thermal cooker, or a vacuum flask 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.
The earliest known thermal cooker dates from the Medieval period in Europe. 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. [1]
Medieval instructions for cooking without fire taken from an Anglo-Norman manuscript in the British Library: [2]
Take a small earthenware pot, with an earthenware lid which must be as wide as the pot, then take another pot of the same earthenware, with a lid like that of the first; this pot is to be deeper than the first by five fingers, and wider in circumference by three; then take pork and hens and cut into fair-sized pieces, and take fine spices and add them, and salt; take the small pot with the meat in it and place it upright in the large pot, cover it with the lid and stop it with moist clayey earth, so that nothing may escape, then take unslaked lime, and fill the larger pot with water, ensuring that no water enters the smaller pot; let it stand for the time it takes to walk between five and seven leagues and then open your pots, and you will found your food indeed cooked.
A league is about three miles (five kms), so the length of cooking time is approximately five to seven hours.
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In the mid-1990s steel thermal cookers were developed in Asia, [3] 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.
A vacuum cooker (Chinese :燜燒鍋) is a stainless steel vacuum flask. The flasks come in various sizes ranging from 20 to 40 centimetres (8 to 16 in) in diameter and 25 centimetres (10 in) tall. A removable pot, with handle and lid, fits inside the vacuum flask. The pot and contents are heated to cooking temperature, and then sealed in the flask. The flask simply reduces heat loss to a minimum, so that the food remains at cooking temperature for a long time, and cooks without continued heating. Note that the food is not cooked in a vacuum. It is cooked inside a vacuum flask. The hollow evacuated wall of the cooker thermally insulates its contents from the environment, so they remain hot for several hours.
Thermal cookers appeal to Cantonese cooks because many Cantonese dishes require prolonged braising or simmering. When these cookers were first introduced in the US, they sold very quickly in the larger Asian supermarkets.[ citation needed ] The slow cooker is used for a similar purpose; but instead of minimising heat loss, sufficient heat is applied to the non-insulated slow cooker to maintain a steady temperature somewhat below the boiling point of water. A slow cooker allows any desired cooking time; the more energy-efficient vacuum flask must cook within the time taken for the food to cool below cooking temperature.
Thermal cookers with two inner pots allow two items to be cooked at the same time, such as curry and rice. All thermal cookers are capable of cooking many dishes from soups to puddings. Cakes and bread can also be cooked by partly submerging the cake/bread tin in boiling water.
The pot is filled with food and water and heated to cooking temperature outside of the flask on a stove, usually to boiling. It is then sealed inside the vacuum flask for several hours. The flask minimises heat loss, keeping the food hot enough to continue cooking and avoid bacterial growth for many hours. [4]
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If a large part of the cooking time is spent at temperatures lower than 60 °C (as when the contents of the cooker are slowly cooling over a long period), a danger of food poisoning due to toxins produced by multiplying bacteria arises. It is essential to heat food sufficiently at the outset of vacuum cooking; 60 °C throughout the dish for 10 minutes is sufficient to kill most pathogens of interest, effectively pasteurizing the dish. [6] Some foods, such as kidney beans, fava beans, and many other varieties of beans contain a toxin, phytohaemagglutinin, that requires boiling at 100 °C for at least 10 minutes to break down to safe levels. The best practice is to bring briefly to a rolling boil then put the pot in the flask. This keeps it hottest longest. With big chunks of food, boil a little longer before putting into the flask.[ citation needed ]
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Variants of thermal cooking, though a better name would be "heat retention" cooking:
A different kind of vacuum cooker is used in the candy manufacturing industry to cook candies at low air pressures.
Sous-vide cooking is cooking at temperatures under boiling, usually in a plastic bag.
Poaching is a cooking technique that involves heating food submerged in a liquid, such as water, milk, stock or wine. Poaching is differentiated from the other "moist heat" cooking methods, such as simmering and boiling, in that it uses a relatively lower temperature. This temperature range makes it particularly suitable for delicate food, such as eggs, poultry, fish and fruit, which might easily fall apart or dry out using other cooking methods. Poaching is often considered a healthy cooking method because it does not use fat for cooking or flavoring the food.
Pressure cooking is the process of cooking food under high pressure steam and water or a water-based cooking liquid, in a sealed vessel known as a pressure cooker. High pressure limits boiling and creates higher cooking temperatures which cook food far more quickly.
A vacuum flask 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. When used to hold cold liquids, this also virtually eliminates condensation on the outside of the flask.
Cookware and bakeware is food preparation equipment, such as cooking pots, pans, baking sheets etc. used in kitchens. Cookware is used on a stove or range cooktop, while bakeware is used in an oven. Some utensils are considered both cookware and bakeware.
Outdoor cooking is the preparation of food in the outdoors. A significant body of techniques and specialized equipment exists for it, traditionally associated with nomadic cultures such as the Berbers of North Africa, the Arab Bedouins, the Plains Indians, pioneers in North America, and indigenous tribes in South America. These methods have been refined in modern times for use during recreational outdoors pursuits, by campers and backpackers.
A rice cooker or rice steamer is an automated kitchen appliance designed to boil or steam rice. It consists of a heat source, a cooking bowl, and a thermostat. The thermostat measures the temperature of the cooking bowl and controls the heat. Complex, high-tech rice cookers may have more sensors and other components, and may be multipurpose.
A slow cooker, also known as a crock-pot, is a countertop electrical cooking appliance used to simmer at a lower temperature than other cooking methods, such as baking, boiling, and frying. This facilitates unattended cooking for many hours of dishes that would otherwise be boiled: pot roast, soups, stews and other dishes.
A tajine or tagine is a North African dish, named after the earthenware pot in which it is cooked. It is also called maraq or marqa.
A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize drink and other food materials. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful or as expensive as traditional stoves, and advanced, large scale solar cookers can cook for hundreds of people. Because they use no fuel and cost nothing to operate, many nonprofit organizations are promoting their use worldwide in order to help reduce fuel costs and air pollution, and to help slow down deforestation and desertification.
Sous vide, also known as low-temperature, long-time (LTLT) cooking, is a method of cooking invented by the French chef Georges Pralus in 1974, in which food is placed in a plastic pouch or a glass jar and cooked in a water bath for longer than usual cooking times at a precisely regulated temperature.
The following outline is provided as an overview of and topical guide to food preparation:
A kamado is a traditional Japanese wood- or charcoal-fueled cook stove.
A haybox, straw box, fireless cooker, insulation cooker, wonder oven, self-cooking apparatus, norwegian cooker or retained-heat cooker is a cooker that utilizes the heat of the food being cooked to complete the cooking process. Food items to be cooked are heated to boiling point, and then insulated. Over a period of time, the food items cook by the heat captured in the insulated container. Generally, it takes three times the normal cooking time to cook food in a haybox.
Cooker may refer to several types of cooking appliances and devices used for cooking foods.
Wonderbag is a stand-alone, non-electric insulated bag designed to reduce the amount of fuel required in the cooking of food in developing countries. Instead of being placed on a stove for the duration of the cooking period, food is instead heated to a hot enough temperature then transferred to the Wonderbag, which uses the principle of thermal insulation to continue cooking, and keeps food warm without needing additional fire or heat. Working on the principle of thermal cooking, the Wonderbag is estimated to save up to 30% of the total fuel costs associated with cooking with Kerosene ("paraffin") alone. In developing countries there are numerous advantages for the product, as it immediately helps ease deforestation of natural reserves, and it frees up those who would spend their time gathering the extra wood for fire fuel.
A multicooker is an electric kitchen appliance for automated cooking using a timer. A typical multicooker is able to boil, simmer, bake, fry, deep fry, grill roast, stew, steam and brown food.
Anova Culinary, officially known as Anova Applied Electronics, Inc., is a company headquartered in San Francisco that specializes in smart kitchen appliances designed for home cooking. Their product range includes devices such as sous-vide cookers, combination ovens, and vacuum sealers. In 2014, Anova introduced the Anova Precision Cooker, the first sous-vide cooking device with Bluetooth connectivity, followed by a Wi-Fi-enabled version in 2015.
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