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Wednesday, July 15, 2009

The thermal cooker

An energy saving, healthful way to cook.

What is a thermal cooker and how does it work?

A thermal cooker (also called a thermal cooking pot) works much like a crock pot. It is made up of two pots:

  • Insulated outer pot

  • Stainless Steel inner pot

The food is put to the boil on the stove in the inner pot before being placed in the outer pot. The heat (from the boiling process) is retained inside the pot, allowing the food to continue cooking slowly.

The cooker is excellent for soups and stews, anything you would normally use a slow cooker or crock pot for.

The thermal cooker can also retain cold temperatures, and can thus function as an ice-box or wine cooler.

Diagram from Thermos Shuttle Chef.
Diagram from Thermos Shuttle Chef.


  • Saves gas and electricity as food cooks in its own heat.
  • Fast and convenient, in most cases needing only 10-15 minutes to bring ingredients to a boil.
  • As it doesn't use gas and electricity once the dish is sealed into the outer pot, you can safely leave the house as the food is cooking.

  • As this is a slow cooking method, it is possible to cook the protein (meat) till tender and still have the vegetables retain their shape and texture.

  • Excellent for picnics and hot meals on day trips as it keeps for up to 8 hours.

Estimated cooking times

  • Generally 10-15 minutes to boil, with most foods ready to eat in 2-3 hours.
  • For food with large chunks of meat, you may want to boil/simmer for up to 30 minutes in the inner pot, and leave the food in the pot for 6-8 hours.

Basic cooking method:

  • Put the ingredients into the inner pot, cover with the lid, and place directly on the stove.
  • Bring to the boil, then simmer. This takes 10 to 30 minutes (the simmering time depends on the type of food you're cooking).
  • Then take the inner pot, and place it in the outer pot.
  • Close the lid tightly.

  • Leave the dish in the pot for a length of time (the minimum amount of time required to cook the dish depends on the type of food you're cooking).

Points to watch out for when using the cooker

  • The inner pot should be about 80% full. The more the contents inside the pot, the more it will retain heat (Any air inside will rapidly reduce the temperature).
  • Do not open the pot before the full cooking time for your dish has been reached, as doing so causes rapid loss of heat.
  • Do not leave the food in the pot longer than the amount of time specified in the manufacturer's guidelines (usually up to 6-8 hours). If you leave the food longer than that, the temperature may have dropped to a level where bacteria can start to grow.
  • If the food takes approximately 6-8 hours to cook, and you plan to eat it a few hours after that, you can reboil the inner pot and its contents before the 8 hours is up and then put it back into the outer pot.


There are many brands of thermal cookers in the market, though the most well-known products are probably Zojirushi Thermal Cooking Pot, the Thermos Shuttle Chef and the Tiger Thermal Magic Cooker.

Question: Can I buy cheaper alternatives to the well-known brands?

My family has actually used thermal cookers made by different manufacturers, and find that the cheaper products do work for most dishes.

However, the more well-known (and more expensive) products definitely do provide better heat distribution and retention.

The cheaper products may require you to cook on the stove for a longer time than what I've indicated on this page, as the stainless steel used to make the inner pot may be of lower quality. I also would be careful how long I leave the food in the pot, as heat loss may be more rapid.

Question: What are the types of thermal cookers available?


The most effective would be the larger ones (around 4 to 5 litres or more). A friend of ours who used a smaller thermal cooker found that it doesn't cook that effectively, and is more useful for keeping food warm.

Two inner pots version.

Some brands do offer versions which include two pots, allowing you to cook two dishes at the same time.Just note that you have to use both pots. If you're cooking only one dish, then you need to boil water in the other pot, and put it in as well, otherwise there won't be enough retained heat to cook the food.

I've also seen versions with a full-size inner pot, and an additional smaller inner pot that slots onto the top of big pot. Obviously, with these types, you have the option of(1) using the big inner pot with the small inner pot to cook two dishes; or (2) you use the large pot by itself.

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