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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?

trejder
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  • And is there any discernible difference between the tea made at 96C versus 100C? – David Richerby Oct 21 '14 at 08:49
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    Ask those guys, who are responsible for writing "Use 96C water" not "Use 100C water". – trejder Oct 21 '14 at 14:03
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    When they say 96°C, I think it is safe to assume that you can boil the water and pour it straight on the tea leaves. Don't overthink, but if you do, get a cheap instant digital thermometer, I use one for green teas. – Max Oct 23 '14 at 19:24
  • I normally see tea vendors round with 5ºC so 100, 95, 90, 85 etc. It really doesn't have to be this exact. With 96, the vendors most likely means to just let the water cool down slightly. To reach 96, I would pour the water after boiling into a pitcher and then pour it into the teapot. – Lisa at Teasenz.com Jul 12 '19 at 06:59

5 Answers5

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Seconds, not minutes. Just the act of pouring the water will cool it slightly. At sea-level pure water will be 100C at a full boil, the temperature will drop immediately when it's no longer being heated.

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. I poured the water into the mug and held the thermometer in the center of the mass of water. 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. This time after the 30 seconds it took my thermometer to stabilize, I got 96C.

I'd say that just by doing this (with a warmed ceramic teapot), you'd have your 96C if you moved quickly.

96

Photo from Instructables

Community
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Jolenealaska
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    I can confirm this (for coffee in a french press you need a similar temperature). Waiting for the water in the pan to drop down to the right temperature took several minutes, but I found that if I poured the water in a thin stream from relatively high up, it would be down to about 95 in the french press. This also means that if you want _exactly_ 96 degrees, you should pour with a thick flow from low height so it's in the pot above 96 and wait for it to drop before you add the tea leaves. – Peter Oct 20 '14 at 16:20
  • I also did this experiment today. I poured some water boiled by an electric kettle to an unwarmed heat-insulated mug. The water temperature inside the mug was 92°C. – cartoonist Jan 18 '19 at 13:27
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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. 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. This ensures it is boiling, as the steam pressure required to move the steam to heat the element doesn't exist until the water is at a full boil.

As such, you can't assume any specific temperature from the kettle without knowing your altitude, and most accurately taking the temperature yourself. 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.

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. 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.

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]

(I can't source that actual statement, as [3] doesn't go to a page that uses this language, but it's within reason compared to other similar pages.)

Joe M
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  • I just looked on Amazon. Every single electric kettle in the top 5 sellers claims to *boil water*. The one I had in college, many moons ago, certainly did. I used it for ramen, and I remember clearly. – Jolenealaska Oct 20 '14 at 22:54
  • Typical-"The Ovente KG83B Black is a high class glass designed electric kettle that looks great on any kitchen or countertops. With 1.5 liter water capacity and 1100-watt of power -- this electric kettle can quickly bring water to a rolling boil. It is proven to be 85 percent more efficient than stovetop kettle that can reduce your daily electricity use." That one is glass, you can *see* the water boiling. – Jolenealaska Oct 20 '14 at 23:02
  • Where did I say it wasn't boiling the water? The element turns off at 85 degrees, but that's because it's nowhere near the water. It's being heated by steam, and turns off when it hits 85. The water has to be boiling to produce that amount of steam. – Joe M Oct 21 '14 at 00:53
  • @Jolenealaska Updated the answer to make that more clear hopefully. – Joe M Oct 21 '14 at 00:58
  • Gotcha, it's clear now. The fact is that 100C water only needs to be poured to reach 96C. A thermometer and knowing your altitude is really irrelevant (unless you're one of the few people who live below sea level), since you're never going to pour water over 100C anyway. – Jolenealaska Oct 21 '14 at 02:30
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    @Jolenealaska Actually, altitude *is* relevant. If you live at about 1,200m (4,000ft), water boils at 96C so will have cooled below that however you pour. Almost the whole state of Colorado is above 5,000ft, where water boils at 95C and it's impossible to make tea with 96C water. – David Richerby Oct 21 '14 at 08:54
  • @DavidRicherby, Of course, but you're not going to be able to change that. That's why it is moot. You're not going to be able to get 96C water tomorrow either. What good does a thermometer do? It's not going to change anything. I'm kind of working under the assumption here that people in Denver know they're not in New Orleans. The hottest you can get is the hottest you can get. Knowing exactly what that temperature (or whether you're 4500 or 5000 feet above sea level) changes nothing. – Jolenealaska Oct 21 '14 at 11:10
  • Well, the question was "How do I get 96C water to brew my tea?", in which case a thermometer is needed to know if it gets to 96C. From a practical perspective of course you're right, but I was just answering the question as asked. – Joe M Oct 21 '14 at 14:26
  • I have to say I was still confused while reading this answer. When you say a kettle doesn't normally "heat to a specific temperature and stop," it's a little misleading, since most people don't carry their kettles around on long trips. They use them at a *specific location* at a specific altitude, and thus their kettle will always stop heating *at the boiling temperature for their altitude*. If you observe the water at a full boil, it will be at whatever that temperature is, **to an accuracy that is probably more reliable than many kitchen thermometers**. – Athanasius Nov 13 '14 at 20:06
  • @Athanasius The kettle doesn't heat to a specific temperature and stop, as in it doesn't heat to 98.2°C. It heats until enough steam is produced to heat up the bimetallic switch (which means the water is boiling, so whatever temperature boiling is at that location). This is important because of the original question, which was how to tell when the water was precisely 96°C (a specific temperature not dependent on the location). – Joe M Nov 13 '14 at 20:32
  • I understand what you meant; I'm saying the wording of the answer still is confusing. For people who may not know the details, they may not understand that having a full boil in a kettle is actually a *very* accurate way to get to a very precise temperature, and once you achieve that boil you'll hold to that very precise temperature. As for the rest, the title of the question is "what is temperature after electric kettle switches off?", which I also take to be an element of the question. The answer to *that* question is pretty reliable, assuming a functioning kettle and knowing the altitude. – Athanasius Nov 13 '14 at 20:48
  • By the way, I'm not trying to be argumentative here **at all**. I just was confused a bit while reading your answer, and then I read the comments, and then I understood what you were trying to say, but then I still thought the answer might be confusing to some. – Athanasius Nov 13 '14 at 20:51
  • @Athanasius Understood, totally happy to clarify things. Thanks for the suggestions! I've made some edits to hopefully clarify. – Joe M Nov 13 '14 at 21:15
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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) 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).

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.

MikeyB
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    The level of dissolved material in tap water will make no discernible difference to the boiling point: fractions of a degree at most. Altitude is probably more significant: every extra 300m above sea level cuts the boiling point by about 1C. – David Richerby Oct 20 '14 at 20:59
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Pure water boils when its vapour pressure equals atmospheric pressure. Pure water will only boil at 100 degrees at sea level if the atmosperic pressure happens to be 1 atmosphere (760mm of Hg)

The boiling point of water therefore depends on two things. 1. How pure it is. 2. What the atmospheric pressure is where the water is being boiled.

In general terms the higher you are above sea level the lower the atmospheric pressure. Atmospheric pressure also changes daily with the weather systems passing through.

It is extremely unlikely therefore that you will ever get water to boil at 100 degrees Celcius.

If you live 4000 feet up the side of a mountain and it's a low pressure day your water will boil below 96C

Ian
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  • The question isn't just about the boiling point, but about how fast it cools off once it's no longer actually boiling since the heat source has been removed. – Cascabel Oct 21 '14 at 05:55
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Electric kettles regulate their set temperature with either a thermocouple or a resettable thermal fuse. 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. That means that the only way to be sure is with a thermometer; used not just once, but every week or two.

Wayfaring Stranger
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    But...but...if the water is boiling, it's boiling. – Jolenealaska Oct 20 '14 at 14:15
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    @Jolenealaska -Some of these heaters are designed to just get very hot, without actually boiling the water. Those are the type I'm talking about. Yeah, boiling is boiling hot, unless you're at 4000 meters. – Wayfaring Stranger Oct 20 '14 at 14:25
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    I'm sorry but this is nonsense. Every electric kettle I have ever used has heated the water until it is boiling vigorously and then stopped. As @Jolenealaska says, when it's boiling, it's boiling and the temperature that water boils at is 100C at sea level, minus about 1C for every 300m of altitude. – David Richerby Oct 20 '14 at 21:03
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    I'm fairly sure most electric kettles identify steam pressure in order to turn off. Mine specifically says not to use it with the top open, as it won't generate the right pressure to know to turn off. This is much easier to correctly measure than temperature: you just need a mechanical switch that has a low-but-nonzero amount of force required to change it, pushing against a spring or somesuch. – Joe M Oct 20 '14 at 22:06
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    Ah, no, it's a bimetallic switch, but in the *handle* (on top) of the pot, that steam has to heat up - hence it not working if the top is open, because not enough steam hits the handle. http://www.mosi.org.uk/media/33871691/electrickettles.pdf for example. So it's not really measuring the temperature of the water - it's really going at something like 85C to ensure it works sufficiently quickly - but the temperature of the steam, which has to exist if the water's boiling. – Joe M Oct 20 '14 at 22:17
  • So you're saying the water *is* boiling. Ergo, assuming sea-level and reasonably pure water, the temp of the water *as it boils* is 100C. What is the disagreement? – Jolenealaska Oct 20 '14 at 23:06
  • @Jolenealaska Some heaters, for example the one under your drip coffee pot, never let the water actually get up to boiling temperature. – Wayfaring Stranger Oct 20 '14 at 23:11
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    @WayfaringStranger That's not an electric kettle, that's a drip coffee maker. – Jolenealaska Oct 21 '14 at 02:25
  • @Jolenealaska It's an object which you're familiar with that behaves in the same way as the type of electric kettle I'm talking about. – Wayfaring Stranger Oct 21 '14 at 06:26
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    WayfaringStranger I have never, in my life, in all the places I've lived, in all the people's houses I've visited, in all the hotels I've stayed at, in multiple countries on two continents, seen an electric kettle that works in the way you're describing, rather than in the way that @JoeM describes. – David Richerby Oct 21 '14 at 08:47
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    @DavidRicherby I had one, used it for making tea 70's through 85 or so, when it crapped out. Now I use a kettle on the stove. Perhaps it was a rare device. – Wayfaring Stranger Oct 21 '14 at 13:14