You’ve seen these two products on the market. You know their function, what they are used for in the kitchen. You’ve seen many different brands out there as well. You are confused if these two kitchen-must-haves have any difference at all.
This article is to tell you, they have no difference at all in terms of functionality but they do have a difference in terms of technology. Both of the kitchen wares do keep your soup or stew warm for long periods of time but one uses electricity while the other one does not. We shall make some simple comparison (without sounding like a science lesson here) between the two of them. Let’s start with the slow cooker first.
The slow cooker uses electricity with a thermostat attached at the bottom of the pot to keep the soup/stew warm throughout the day or any long periods of time. Since it’s a thermostat, of course you can adjust the desired temperature to be kept at. The inner pot is using the “conventional Chinese method” of retaining warmness that is, using some stone material such as ceramic or porcelain. Electricity is supplied to the thermostat and it produces heat constantly to the temperature that is set and this heat is constantly “transferred” into stone inner pot from the bottom. Heat convection takes place within the inner pot. Since the inner pot is made of thick stone material, heat loss still takes place but at a slower rate.
If you notice the inner walls of the outer pot of the slow cooker, you can see it is glossy surface. This further slows down the rate of heat loss using the laws of radiation. As for the top of the inner pot, the lid is usually made of thick glass material to prevent heat loss as well.
This is how the slow cookers works and remember the fact that it uses electricity to achieve heat retention.
Now let’s move on to thermal cookers. To put it simply, it makes use of the same heat transfer theory as what you have known or learnt from vacuum flasks in physics during school or anywhere. It uses the laws of heat convection, conduction and radiation to help aid in heat retention.
Heat conduction and convection is reduced greatly (but not totally as this is not possible) by means of vacuum. Vacuum is a better insulation compared to foam. Now at the sides or walls of the thermal pot, there is an outer wall and inner wall. In between these walls is the vacuum. With the presence of vacuum (okay okay, I promise no science lessons here but just good to know that vacuum contains close to zero number of atoms), heat conduction and convection is greatly slowed down.
Infrared radiation is reduced by means of the silvering linings (like a mirror) on the sides or walls of the outer pot. In addition, the double lids (the inner pot lid and the outer pot lid) and the insulation support at the bottom of the thermal pot helps reduce the process of heat loss. With the combination of vacuum and silver linings, it greatly reduces heat transfer by convection, conduction and radiation.
If a vacuum flask can retain temperatures of both hot and cold for long periods of time under the same heat transfer theory, a thermal pot can do so too.
Now that we know how thermal cookers work, we proceed to compare how different they are to slow cookers.
Electricity: the slow cooker uses it while the thermal pot does not and therefore it saves money.
Safety: the slow cooker needs to be turned on for as long as you want you soup/stew to be warm. The thermal (inner) pot needs only 10-15 minutes on the gas stove before placing into the outer pot for it to self-cook. Both scenarios are assuming that you are out at work and not at home to look after the soup/stew.
Versatile: the slow cooker needs a power point all the time for it to operate and hence not convenient to bring out for picnics or any outdoor activities. The thermal pot, since it can self-cook the moment it leaves the gas stove, can be brought to almost anywhere for up to 8 hours.
Multi-function: the slow cooker can only deal with warm-hot purposes. The thermal pot can deal with both hot and cold (such as using it as an ice-box or keeping cold drinks) purposes.
Cooking ability: the slow cooker have a higher chance of “overcooking” when compared to the thermal pot. Since the thermal pot is a much slow cooking (and “natural”) method, foods such as vegetables and meat will be retain in terms of colour and tenderness. Soups in thermal cookers have been reported to remain clear after being left “alone” after a day of work. This is based on actual experiences from real users of the thermal pot who have switched over from slow cookers.
Convenience: the slow cooker has to be set to the right temperature in order for it to slow cook the soup/stew properly. The thermal pot does not need temperature adjustments as all you have to do is to leave the inner pot on the gas stove for 10-15 minutes and place it back into the outer pot.
This article thoroughly understands how both types of cookers work and the science behind it. With these understandings, it becomes clear that the thermal pot stands out as the most convenient and money-saving option to cook up a nice warm soup/stew with tender meat and well-coloured vegetables within, after a hard day’s work.