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I've heard the advice that water should be boiled for tea only one--that when boiled it loses dissolved oxygen, and if there is insufficient oxygen in the water, the flavor of the tea is (somehow) affected.

This doesn't seem to make sense to me. If the water loses oxygen when it is boiled, it would have lost it before tea ever touched it anyway.

Does this really make a difference, or is it just a commonly perpetuated kitchen myth? If there is one, what affect does the oxygen (or lack) have on the finished product?

Ray
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    English people I know (including my mother) will also insist you not make tea using water from the hot tap, again saying that oxygen (dissolved air actually) comes out of it when it's hot. Some will refuse to use even water that has sat around - say, was put into a kettle but never heated up - starting with fresh cold water from the tap every time. You could do an experiment so you would know whether you needed to always do it the hard way, but I don't recommend trying to use the results of their experiments to show them they are wrong, nor doing it the "wrong way" when they can see you. – Kate Gregory Oct 10 '11 at 22:47
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    Interesting.. in the US, we avoid hot water from the tap because it tends to carry more sediment – Ray Oct 10 '11 at 23:18
  • @Kate, I'm surprised that they're not complaining that the water coming out of the hot tap is too cold. Tea should be made with boiling water. – Peter Taylor Oct 11 '11 at 12:34
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    @Peter good one. To be clear, they object to filling the kettle from the hot tap. I see it as a time saver but apparently the air loss is all that matters. – Kate Gregory Oct 11 '11 at 12:44
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    @Kate, oops, that was a genuine misunderstanding. I clearly failed to extract as much caffeine as usual from my coffee. – Peter Taylor Oct 11 '11 at 19:19
  • Surely any water still left in the kettle hasn't reached 100 degrees? Once water reaches 100 degrees it evaporates? –  Aug 18 '15 at 08:29
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    @Myles Water doesn't instantly boil when it reaches the boiling point - it can exist as both liquid and gas at 100C. Once it reaches 100C, it takes additional energy (and time) to turn it all to water vapor. – Cascabel Aug 18 '15 at 16:21
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    @KateGregory English people insist you don't use the hot tap for food use because our hot water supply often comes via grotty tanks that render the water unfit for human consumption. Any other explanation means, in reality, "I heard you shouldn't use the hot tap but I'm not really sure why. I guess maybe it's X." Boiling water removes essentially all dissolved gas from that water so, it really doesn't matter how much gas was dissolved in the water before it went in the kettle. – David Richerby Apr 06 '18 at 08:31
  • I don't have an scientific explanation, but the taste of water is for sure affected. This won't be easily noticeble when you use it to steep a black tea from tea bag. But if you steep a light, yet delicate green tea, the taste will be noticeably different. The texture of the tea can also become somewhat thinner when using reboiled water. – Lisa at Teasenz.com Apr 09 '19 at 19:55

6 Answers6

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All moving water has dissolved oxygen in it. That is what fish breath

Dissolved oxygen is reactive, and will most likely extract more substances from the tea leaf, than without it. If these are the good flavour parts of tea, I do not know?

When you heat water it starts to release the dissolved oxygen. The more you heat water the more oxygen escapes

You can buy tea making kettles that bring water up to 95°C (203°F), but not boiling, so as to decrease the amount of dissolved oxygen lost, but still making the water hot enough to brew tea. They also save energy :-) I use one of these, and am happy with it

Example Kettle

Some people "watch" their kettle, and switch it off just before the water boils!

It is a personal taste preference if tea tastes better when brewed in water with more dissolved oxygen or not

TFD
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    Now I need to buy one of those pots, to add to the snobbery factor of my kitchen! – Flimzy Oct 12 '11 at 22:46
  • It's not oxygen content, but impurities react to boiling https://www.newscientist.com/article/mg15420808-100-the-last-word/ – Binary Worrier Apr 04 '18 at 11:22
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    "Dissolved oxygen is reactive, and will most likely extract more substances from the tea leaf." That seems dubious, to me. The way that oxygen "extracts" things is called "burning". – David Richerby Apr 04 '18 at 14:44
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    "The more you heat water the more oxygen escapes" - The more means the time, the temperature, or both? – arieljannai Apr 27 '18 at 20:10
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    @DavidRicherby DO could react and oxidize compounds in the tea water, but this would likely destroy or denature them. – MarsJarsGuitars-n-Chars Jun 17 '18 at 23:11
  • -1 because the real thing here is heat and dissolved oxygen(DO). Your claim about 'reactive, and will most likely..' is dubious at best with no foundation. – MarsJarsGuitars-n-Chars Jun 17 '18 at 23:12
  • @MarsJarsGuitars-n-Chars Yes but that reaction is the same reaction that occurs when you burn whatever substance. And burning usually isn’t good. – David Richerby Jun 17 '18 at 23:37
  • @DavidRicherby Agreed. It is called oxidation in food science. Apples, bananas, red meat. – MarsJarsGuitars-n-Chars Jun 18 '18 at 13:07
  • I think one could more easily add more oxygen than prevent it's loss. Pouring through the air a few times should do it (it seems to be just agitation and exposure) – Megha May 20 '19 at 04:28
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This blog article (citing numerous sources) claims that re-boiling water doesn't have any significant effect on tea taste. Here are some key points from it:

  • Heating water above 50˚C already removes most of the oxygen from it, so neither once-boiled nor twice-boiled water contain significant amounts of oxygen.

  • Triangle tests such as this one prove that dissolved oxygen by itself doesn't affect water taste.

  • While oxygen could theoretically reduce tannin's concentration in tea, this effect is dwarfed by other factors, notably steeping time, water temperature, and water/tea ratio.

All this is not to say that water is unimportant. Water is important. Alkalinity is important. Salt content is important. Minimal iron content is super important. Dissolved oxygen is not important. [...] For brewing tea, coffee, or any other hot beverage, dissolved gases are irrelevant.

Tazik_S
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Dmitry Grigoryev
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I agree with your suspicion. While boiling water most likely does cause it to lose some of its oxygenation, the bubbles and steam you see while boiling water do not come from the oxygen trapped in the water.

Water boils when you heat it enough for the water to begin acting as a gas. The reason boiling water bubbles is because the heat source is generally on the bottom, so the first water molecules to become gaseous are on the bottom and then bubble up.

Saying boiling water releases its inner oxygen is akin to saying that ice is not water and in fact simply traps water inside.

If you're worried about oxygenation, try pouring your cup of tea in various methods:

  1. boil it in the mug (microwave?)
  2. boil then pour into a cup
  3. boil then pour a few times in to a cup
  4. get a straw and blow some bubbles in your cup
  5. try using seltzer water to make tea...?

Anyways, I could be wrong, but the whole concept seems a little silly.

Happy tea drinking :]

Madeline Trotter
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    If you boil it in the mug, be careful to only boil it once. Boiling it a second time can result in a dangerous and spontaneous boil over. Basically, boiling it twice can superheat the water and remove any nucleation points, so when you dump in your coffee or tea it all boils at once. – Nathan Oct 11 '11 at 01:54
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    @Nathan: That can happen on the first boil, too. I've seen it happen when my gf was trying to make instant coffee (for lack of a better alternative at the time). Fortunately, she wasn't burned by it. – Dave Sherohman Oct 11 '11 at 10:03
  • Boiling water removes essentially all of the dissolved gases. It doesn't matter how you boil the water: if it comes to a rolling boil, all the gas leaves. (Yes, the big bubbles you see when water boils are primarily steam, but they carry all the dissolved gases with them.) Meanwhile, the bubbles in selzer water are carbon dioxide and have nothing to do with oxygen. Boiling selzer water will drive off all the carbon dioxide, along with whatever other gases were in there. – David Richerby Apr 04 '18 at 14:41
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This person found that increased oxygen in the water resulted in milder, less tannic tea:

https://cookingwithnumbers.wordpress.com/2016/01/09/does-oxygenating-water-improve-tea/

Rather than boiling and reboiling water, they oxygenated water by bubbling air through it - so it doesn't exactly indicate what the effect would be from repeated boiling.

Cascabel
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aikramer2
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  • Presumably the repeated boiling would decrease the dissolved oxygen in the water, having opposite effect of aeration, thus increasing the solubility of the water, actually suggesting that you should boil water extensively before using for tea. – aikramer2 Jan 09 '16 at 03:38
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My mom, who would have been 100 years old by now, always told us that reboiling the water leaves the water a bit "stale" tasting. She talked of "Free Oxygen", which I believe was her way of saying Dissolved Oxygen. I think DO is what fish actually get through their gills, which is why fish in a bowl need to get fresh water (with DO at high enough levels) in order to live. So - my theory is that tea is best when made with fresh water that hasn't been previously boiled. That's my 2 cents!

user42839
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    My head hurts... That's as clear as a mud puddle. – NKY Homesteading Jan 25 '16 at 22:53
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    OK, but you're making tea, not keeping fish. You've explained why fish need oxygen, but not how or why it helps tea. And the first boiling already removes essentially all the dissolved gases from the water, so reboiling it will make no significant difference. – David Richerby Apr 04 '18 at 14:43
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All the correspondents seemed to have mislaid the chemistry and physics from early school lessons as I remember water is composed of two atoms of Hydrogen and one of oxygen, if one were to remove the oxygen as suggested then to be sure we are left with H2 which at NTP (normal temperature and pressure) occurs as a highly flammable gas, plus you would need a chemical reaction (catalysis) or electrolysis to separate O from H2 , boiling water is simply heating water until the vapour given off equalises atmospheric pressure which is one bar or one atmosphere in old money, as a matter of interest Marks and Spencers have a message on their tea packets that boiling water removes the Oxygen, a case I think for appropriate legislation enforcement.

Tom Gilmore

Tom Gilmore
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    Tom, you might have misunderstood the idea in the question and answers. We're not talking about losing the oxygen bound in the H2O molecule--we're talking about oxygen gas (O2) dissolved in the water. You may not be considering that gasses can dissolve in liquids; consider for example club soda, in which CO2 is dissolved in water. – Ray Aug 22 '14 at 16:08