Vacuum flask cooking

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Vacuum flask cooking was introduced to the Asian market in the mid-1990s. The vacuum cooker (燜燒鍋) is a stainless steel vacuum flask. The flasks come in various sizes ranging from 20-40 cm (8-16 in) in diameter and 25 cm (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.

Vacuum flasks 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.

1 Usage
2 Advantages
3 Disadvantages
4 Notes
5 See also
6 External links

[edit] Usage

The pot is filled with food and heated to cooking temperature; it is then sealed inside the vacuum flask for several hours; the flask minimises heat loss, keeping the food hot enough to continue cooking.

[edit] Advantages

A vacuum flask cooker cooks food expending only enough energy to heat the pot and contents to cooking temperature; the food is cooked by the stored heat, as the flask drastically reduces heat lost to the environment. 10 to 20 times less energy is required to cook this way than using conventional methods without thermal insulation^{[citation needed]}.

Cooking this way is convenient for people with little free time, and activities away from home. For example, a domestic user may prepare a meal, then spend many hours away from home—working at a job, for instance—returning to food ready to eat.

[edit] Disadvantages

A large part of the cooking time is spent at a temperature which allows bacteria to grow in the food, with a danger of food poisoning due to bacterial infection, or toxins produced by bacteria. It is essential to heat food to a safe temperature before vacuum cooking—60°C for at least 10 minutes will kill most temperature-sensitive bacteria. If the bacteria are all killed before the food cools below this temperature, they will not be available to multiply.

[edit] Notes

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.
A different kind of vacuum cooker is used in the candy manufacturing industry to cook candies at low air pressures.

[edit] See also

Haybox cooking an earlier form of cooking with retained thermal energy.
slow cooker a non-insulated cooker which is thermostatically heated to about 80°C for unattended cooking for many hours.
Vacuum flask what a vacuum flask is and how it works.