Vacuum flask cooking

The picture shows a vacuum flask cooker with the pot inside.

The picture shows a vacuum flask cooker with the pot taken out.

Vacuum flask cooking was introduced to the Asian market in the mid-1990s. The vacuum cooker (燜燒鍋), often called a thermal cooker in English, 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.

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.

The historical equivalent of the vacuum cooker is the haybox, nowadays perhaps using more modern insulating material than the original hay or straw. This works on the same principle but has much poorer heat retention.

Method

The pot is filled with food and heated to cooking temperature, 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.

Some flasks also come with 2 or 3 smaller pots so you can cook 2+ dishes at once.

Advantages

• long cooking means more tender meat^[1]
• minimizes fuel, energy use, CO2 emissions^[2]
• Saves water - less evaporation
• Saves food - no burning, no cleanup
• keeps flavour, nutrients in
• convenient - cooks while you are at work or sleeping
• can take while travelling or to picnics
• reduces smoke, odor, humidity, grease buildup in kitchen
• easy cleanup
• Safer - no power cord, outside not hot, spill-proof, reduces injuries
• Reduces toxic fumes which means less respiratory problems and other diseases, particularly in children

Thermal Cooker guide^[3]

Precaution

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 bacterial infection, or 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.^[4] The best practice is to bring briefly to a rolling boil then put the pot in the flask. This keeps it hottest longest.

Variants

Variants of thermal cooking, though a better name would be "heat retention" cooking:

• Wonderbag is an insulated bag to put around pots you already own.
• Haybox cooking uses hay or sawdust to provide the insulation around the pot.

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 and a temperature-controlled water bath in order to have tender, succulent flesh.

See also

• Low temperature cooking
• Sous-vide

References

External links

• Thermal Insulated Cookware Thermos Stainless Steel Cook & Carry System
• Green Cooking Creative ways to cook greener.