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Boiling water is too hot for some teas. Today I heard that it's better to boil water to 100 °C and let it cool down to 80 °C rather than heat water to 80 °C. Is this true? Does it really affect properties of the water, other than killing bacteria?

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    Related: cooking.stackexchange.com/q/73059/33128 – Catija Apr 3 '18 at 12:26
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    As a side note, to avoid boiling to 100 degrees and cooling, there are many electric kettles available now with variable temperature controls e.g.: domu.co.uk/… – WhatEvil Apr 3 '18 at 13:31
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    Just a note related to a comment in the question: heating to 80C already is going to kill almost all bacteria instantaneously. Almost any bacteria that survive at that point will have formed spore forms, and boiling for quite a few common types of dangerous bacteria that can survive such conditions may not be sufficient to kill them. In sum, there's very little safety benefit to heating a few degrees hotter once you're already at 80C. – Athanasius Apr 3 '18 at 19:31
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    If water is already safe to drink from the tap, little safety is gained by boiling it. – henning -- reinstate Monica Apr 4 '18 at 14:11
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It's actually the opposite, you shouldn't boil water for tea unless you want it boiling. Water has dissolved oxygen in it, the more you have the nicer your tea will taste. This has been covered in this question.

The hotter your water gets, the faster it loses dissolved oxygen, so you'll get better tea (for most people's palates) if you raise your water to 80°C and use it right away. If you boil it and then let it cool you will lose much more O2.

FYI, 80°C is pretty low for most black teas, I experimented with this some years ago and found that most black teas brewed at 80°C came out pretty awful, green tea seemed to be the exception to this. I found 90–95°C to be more of the sweet spot.

Other than boiling to kill pathogens the one thing I can think of would be to purge chlorine from the water, which boiling does. However, you'd need to boil it for 15 minutes to get rid of all of it, not just raise it to boiling. Also, boiling doesn't get rid of chlorinates, which are used to purify water more often these days. See this question for more details on that.

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    And note that boiling water removes essentially all dissolved gases from it. Not much will redissolve in the time it takes the water to cool back to 80°C. – David Richerby Apr 3 '18 at 12:49
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    Right, it takes days for water to re-oxygenate. – GdD Apr 3 '18 at 12:50
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    "Most teas" really depends on what's in your cupboard. For some people 80C is perfect for "most teas". Green and, especially, white teas do well with lower temps. Even some oolongs and delicate "black" teas like Darjeeling do better at lower temperatures. – J... Apr 3 '18 at 13:35
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    You're right @J..., that's subjective. I've changed teas to black teas to clarify. – GdD Apr 3 '18 at 13:37
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    The accepted answer in the link is dubious to say the least. And the alternative answer is not just more plausible but also goes with the golden rule of cuisine: Taste and try before you buy! – TaW Apr 3 '18 at 15:53
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Boiling helps getting the lime out of hard water. In that case, it's better to brew tea with water which had boiled, since lime interferes with brewing process and gives your tea a chalky after-taste.

Edit: Since I got several sceptical comments regarding the statement above, here's a wiki page on temporary hardness, which is due to dissolved lime mineral and can be removed by boiling.

As for dissolved oxygen, I've found an article which claims it has no effect on tea taste, and cites several sources to back up that claim.

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    Boiling would (if anything) concentrate the minerals in en.wikipedia.org/wiki/Hard_water and will certainly not remove them. – Scott Centoni Apr 4 '18 at 18:39
  • For this to work you'd need to boil, then cool to allow the carbonate to precipitate out of the cooler liquid, filter, then boil again. Boiling and cooling to 80C isn't likely to have an effect. You're probably better off using a water filter. – Schwern Apr 5 '18 at 1:33
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    @ScottCentoni If boiling doesn't remove lime from water, then where do these limescale deposits on the heating element come from? – Dmitry Grigoryev Apr 5 '18 at 7:25
  • @AndyT your comments are a great answer to a totally different question (then the one asked by OP). I'd upvote it! :) – I'm with Monica Apr 5 '18 at 9:49
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    @DmitryGrigoryev - Interesting reading, thanks! Previous comments deleted as they're clearly inaccurate, whatever Alexander Kosubek thinks... – AndyT Apr 5 '18 at 10:13
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There's not much difference in taste between the two options. I do recommend to get a water cooker that can boil it just to 80C for two reasons:

  1. It takes 3 minutes or so to let the water cool down from 100 to 80.
  2. When you reheat the water twice to 100C to steep tea, the tea is gonna taste dull. I don't experience when reheating to 80C.

Update: I noticed when I answered the question that I assumed use of bottled water. That's what I use, since tap water isn't great in my country. For tap water, I would recommend to always boil to 100C first.

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Boiling changes the molecular structure of water.

When water is heated, a large part of the heat energy goes into breaking the hydrogen bonds between the water molecules.

https://oli.cmu.edu/jcourse/webui/guest/look.do?context=90d3ff2780020ca601a3f1c414ba7138&confirm=true



Also the pH value goes down.

https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Acids_and_Bases/Acids_and_Bases_in_Aqueous_Solutions/The_pH_Scale/Temperature_Dependence_of_the_pH_of_pure_Water



pH value is a measurement for acidic and alkalic.

The human blood is around the middle on the scale.

The scale goes from 0 to 14.

14 is alkaline.

0 is acid.

You can check with litmus paper.

Most organisms die towards the ends of the scale.

Means, both substances in these areas are poisonous.

Here you will — not — get through boiling, but think like detergent and toilet cleaner.



So better to stop before 80°C for green tea.

And as @GdD says, black tea probably needs more.

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