Forum: cooking.stackexchange.com
Tags: <temperature><tea><boiling><water>
Title: What is water temperature after electric kettle switches off?
Question: My tea preparation prescriptions says to prepare it using water heated to 96 Celsius degrees.   When water heated in standard, typical electric kettle reaches this temperature?  Is it (always?) immediately after switch turns off? Or is it 100 Celsius degrees, and I need to wait approx. 3-5 minutes to get to cool to 96?

Answers:
sents: text: Seconds, not minutes.
text: Just the act of pouring the water will cool it slightly.
text: At sea-level pure water will be 100C at a full boil, the temperature will drop immediately when it's no longer being heated.
text: This is unscientific at best, but just for giggles I put an accurate digital thermometer into a room temperature mug, and brought a couple of cups of cups of filtered (not distilled) water to a boil in a saucepan.
text: I poured the water into the mug and held the thermometer in the center of the mass of water.
text: In the time it took for my thermometer to stabilize on a reading (30 seconds), the water was at 92C. I repeated the mini-experiment using a hot mug that I had heated by boiling some water in the microwave, and pouring it out just before I poured in the boiling water from the saucepan.
text: This time after the 30 seconds it took my thermometer to stabilize, I got 96C.
text: I'd say that just by doing this (with a warmed ceramic teapot), you'd have your 96C if you moved quickly.
text: Photo from Instructables
answer_details: author: cooking.stackexchange.com/users/20183/Jolenealaska
score: 13
sents: text: Basic electric tea kettles primarily work by turning off when a bimetallic switch in the handle (probably at the bottom, where it will require some steam pressure to have steam travel down to) of the kettle is sufficiently heated to deform one of the metals, turning off the kettle.
text: This switch is heated by steam, and the element itself is typically turned off well below 100°C (closer to 85°, perhaps) to ensure it doesn't go on heating indefinitely, particularly well above sea level.
text: This ensures it is boiling, as the steam pressure required to move the steam to heat the element
text: doesn't exist until the water is at a full boil.
text: As such, you can't assume any specific temperature from the kettle without knowing your altitude, and most accurately taking the temperature yourself.
text: It does not heat to a specific temperature independent of altitude/pressure and stop, if you're using one of the cheaper models; if you have a model that has digital temperature control, then of course you can simply set that.
text: Now, the temperature it stops at is quite stable, for your altitude; so if you determine that temperature (either with an accurate thermometer, or by searching the internet and/or doing the math to find out what temperature water boils at where you live) it's likely very consistent.
text: So if you are looking for 96°C, and where you live water boils at 98°C, you can work out how to drop it those two degrees pretty easily.
text: Example information: UK Museum of Science and Industry article about Kettles John Taylor , one of the early inventors of this kind of switch Russell Hobbs , another UK company that pioneered this process, and includes some information as to how it works on the page: The automatic electric kettle K1 (a world first), designed in October 1955, used a bi-metallic strip at the rear of the kettle: steam was forced through an aperture in the lid of the strip and this knocked the switch, turning the kettle off.[3]
text: (I can't source that actual statement, as [3]
text: doesn't go to a page that uses this language, but it's within reason compared to other similar pages.)
answer_details: author: cooking.stackexchange.com/users/23682/Joe M
score: 7
sents: text: Assuming your kettle causes the water to boil (rapid escape of gas/bubbling) and that the water you are using is from a tap (not distilled)
text: then it is very difficult to say exactly the temperature of your water at boiling, but it will be a small amount over 100 Celcius degrees (as impure water has a higher boiling point).
text: To know when your water has reached 96 Celcius degrees, you will need to use a thermometer to test for the exact temperature, which can be reached quicker by pouring into a cool container or pouring between containers.
answer_details: author: cooking.stackexchange.com/users/26801/MikeyB
score: 4
sents: text: Pure water boils when its vapour pressure equals atmospheric pressure.
text: Pure water will only boil at 100 degrees at sea level if the atmosperic pressure happens to be 1 atmosphere (760mm of Hg)
text: The boiling point of water therefore depends on two things.1.
text: How pure it is.2.
text: What the atmospheric pressure is where the water is being boiled.
text: In general terms the higher you are above sea level the lower the atmospheric pressure.
text: Atmospheric pressure also changes daily with the weather systems passing through.
text: It is extremely unlikely therefore that you will ever get water to boil at 100 degrees Celcius.
text: If you live 4000 feet up the side of a mountain and it's a low pressure day your water will boil below 96C
answer_details: author: cooking.stackexchange.com/users/28781/Ian
score: 3
sents: text: Electric kettles regulate their set temperature with either a thermocouple or a resettable thermal fuse.
text: Both devices are likely good to within 10% of their nominal value, and are affected by the amount of lime scale on the bottom of the pot.
text: That means that the only way to be sure is with a thermometer; used not just once, but every week or two.
answer_details: author: cooking.stackexchange.com/users/5455/Wayfaring Stranger
score: 1

Summary of the answers:
Water boils at different temperatures based on altitude, but it will quickly drop from 100 to 96°C when it's no longer being heated or when poured into another container. You can test the exact temperature with a thermometer or work out how to bring the temperature down a few degrees from boiling.
The best way to check the temperature of water is to use a thermometer. This is because the real boiling point of water depends on where you live.