The kettle has been with us in one form or another for many years, many thousands of years in fact. Originally the water was ready when the water was bubbling furiously or large amount of steam was being produced. Which was fine if the kettle was in sight, which it would have been in old time kitchens.
However we can do better than that and so technology gave us the
whistle. As kettles developed a spout for pouring the fitting of a whistle
became practical. This simple device just whistles as steam is produced. The
pitch of the whistle changes as the amount of steam increases
This was a great but simple device and meant that you would know that the water had boiled and would continue boiling until we take the kettle of the source of heat.
When we entered the 20th century we were presented with
electric kettles and although a whistle could be used – there was a better way.
The bi-metallic strip.
The bi-metallic strip, as any school child will tell you, is two strips
of metal connected together but which expand at different rates. The affect is
that instead on expanding along its longest length in a linear way it bends in
an arc. And it’s this feature that’s used to switch the electric kettle off
when the water boils.
So the bi-metallic strip acts like as a heat switch ad has proved very effective and a great safety feature as the electricity to the kettle is switched off and stays off until manually reset. However with the new breed of variable temperature kettles a simple switch has had its day.
Variable Temperature Kettles
These new breed of kettles use a thermocouple thermostat. This is also
quite a simple device, a sensor is used. This sensor has electricity passing
through it and is sensitive to heat. As the temperature increases the voltage
drop over the sensor changes. Electronic circuitry is used to determine the
temperature with a fair degree of accuracy. And thus the variable temperature
kettle was born.
The engineering challenge then becomes – where to place the sensor in a vessel that holds two pints of water. The element at the bottom of the kettle heats the water at the bottom of the kettle first and then by convection the rest of the water heats up. The water in the middle would be slightly warmer than the water touching the sides. So you can see some compromise is need with the placement. These modern kettles can incorporate features that heat the water faster the cold it is and as they get close to desired temperature heat the water slower so that the water is at a fairly even temperature throughout its volume as the as the temperature is reached. And this is good enough for most domestic uses.
So we’ve come a long way from the humble kettle to the latest devices. But each time technology has come along to make the step along the road for this humble of devices.
See our best six variable temperature kettles here