What is a teasmade?

A teasmade is an appliance which is designed for use by the bedside. It combines the functions of an alarm clock and a tea maker, and wakes you up in the morning with a hot cup of tea. The word teasmade is a genericised trademark, currently used for teasmades manufactured under the Swan Products brand.

Teasmades work by transferring water from a kettle to a teapot via a siphoning tube. The principle of siphoning has been known for many hundreds of years, since Egyptian reliefs from 1500 BC show siphons being used to extract liquid, perhaps water, wine, or oils, from earthenware storage jars. [1]

The earliest automatic tea makers consisted of a burner mounted on a wooden base, and a clock to set off the burner at a pre-set time. Above the burner was a glass or metal kettle. The kettle was typically sealed with an airtight bung, or a lid with a rubber seal, so that the only exit for the boiling water and steam was a narrow syphon tube which passed from the kettle out to the teapot. If there were leaks anywhere, or if the rubber seal had perished, pressure would not build up, and the teasmade would not operate. The burner heated the water inside the sealed container until the temperature increased above boiling point. As soon as the vapour pressure in the vessel exceeded atmospheric pressure, it pushed the water up the siphon tube into a teapot, in a sudden explosion of whooshing and gurgling. Continued heating of the remaining water in the vessel maintained the pressure and supported the siphoning process until the system ran out of water. Eventually the water boils, creating steam and huge amounts of pressure, just like a steam train. The pressure forces the water up into the tube, where it is syphons out into the pot.

This basic principle has applied throughout the history of the teasmade, but as technology has developed, additional features have appeared. The heater has been upgraded from a spirit burner, to a gas burner, and eventually to an electric element. A simple addition was a maximum fill level in the kettle. This ensures that as the water heats and expands, there is sufficient space in the kettle to take up the initial pressure as the water comes to the boil, and to prevent the water from splattering out of the spout. Inventors also realised that it was necessary to prevent the teasmade from operating if there was no teapot waiting to catch the expelled boiling hot water. This was done by placing the teapot and kettle on a rocking platform which operated a cut out switch as the weight of water transferred from the kettle to the pot.

Another essential feature was a cut-out switch which could operate after the water had boiled and the teapot had filled. It would turn the alarm on and turn the kettle off. This was achieved with a bi-metallic thermostat attached to the element. These thermostats were reputedly first developed in 1831 by the Scottish physician Andrew Ure. [2] The key to their operation is a contact strip fixed to the element which acts as a bridge in an electrical circuit. This strip is made from two different metals bonded together like a sandwich. Each metal has a different coefficient of expansion, so as the strip heats up, one of the metals expands more than the other and the strip is forced to bend away from its fixed contact point. A suitable contact is welded to the strip which makes contact when the first temperature point is reached to turn on the alarm, and breaks contact when the second temperature point is reached, to cut off the kettle. Without this switch, the element would continue to run, at risk of burning out, blowing a fuse, or even starting a fire.

In practice, the operation of a teasmade is simplicity itself. All you need to do is fill the kettle with water, place the teabags in the pot, and set the alarm. Don't forget to set out your cups or mugs, teaspoons, a bin for used teabags, and some milk, if you use it.

You can use any kind of tea for your teasmade, both loose leaf and teabags are fine. In fact (whisper it quietly) you can even use coffee!

Most teasmade users in the UK find that if they keep milk in a small jug alongside the teasmade, it never goes off overnight. Skimmed milk keeps better because of the low fat content. For warmer climates or hot weather some users favour small catering pots of UHT milk, others keep the milk in a small thermos, or for the ultimate luxury, a select few use a mini-fridge.

[1] A History of Mechanical Inventions, Abbott Payson Usher

[2] Andrew Ure, On the Thermostat or Heat Governor, Philosophical Transactions of the Royal Society of London, 1831