ZeroZen said

Reheat Water - your opinion!

I was wondering – I focused a lot within my tea studies on water. I tried so many bottled waters and other water sources to find the best stuff for my teas. But beside the right water I often heard that many are arguing about not to reheat the water!

I definitely noticed with a huge difference that the wrong type of water can ruin a tea massively but by reheating it after it already boiled ones I haven’t noticed much to be honest! Do you?

Sometimes I miscalculate the amount of water using for a steeping and some is left but after that I still use it again after boiling it a second or sometimes if it is more water even a third time and I never felt any difference I have to admit!

29 Replies
Brian said

i talked with a chemist about this. boiling reduces the dissolved oxygen content of the water (which in turn makes it taste flat). i only re-boil my water once. then pour out and start with fresh stuff….

Nope, I don’t think so. Once you bring water close to a boil the dissolved oxygen is practically zero. Further boiling does not reduce it further. There may be other reasons not to reboil water but DO is not one of them. Feel free to refute the below but if so you’re going to have to provide better sources than “a chemist”:

“The dissolved oxygen hypothesis rests on two premises: (1) that once-boiled water contains more dissolved oxygen than twice-boiled water; (2) that dissolved oxygen improves the flavor of tea. Both premises are demonstrably false.

Boiling itself does not remove dissolved gases. It is the change in temperature or pressure that affects the amount of gas that a liquid can hold (i.e., the solubility of a gas in a liquid). Solubility decreases as temperature increases. Assuming normal atmospheric pressure and composition, water at 0˚C can hold a maximum of ~15ppm DO, while water at 50˚C can only hold ~5ppm. Once the water reaches 100˚C, solubility is zero. Therefore, if you’ve brought water even close to a boil, you’ve removed virtually all the DO. What this means is that neither once-boiled nor twice-boiled water contain significant levels of DO, refuting premise (1)."


And here is Stanford Magazine (they do not mention DO, but that’s the point, they do not mention DO):
“The warning against reboiling water probably goes back to days when water sources were more suspect. Boiling water kills potentially dangerous microbes and parasites, but it can also concentrate inorganic poisons. If you’re using clean water, you can reboil it as many times as you want—it won’t affect the taste or your health. However, if your water comes from a well, all bets are off. Some ground water contains nitrates, found in fertilizer, and arsenic, which may occur naturally or as runoff from farms and industry. Boiling water increases the concentration of those contaminants. The more times you reboil the water, the higher the concentration and the higher the risk.”


I mentioned this below but the chemists of /r/chemistry disagrees with your chemist:

AllanK said

I have always heard that you shouldn’t reheat water because the tea will be flat because of lack of oxygen content in the reboiled water. But I think it is a matter of preference. Some may notice a difference while others may not. I also think it makes less of a difference if you take the remains of your kettle and simply add fresh water to it.

I’ve heard the same, problem is that I have also heard that the dissolved oxygen reaches almost zero pretty much instantly at a boil. In which case this hypothesis is incorrect. I’m trying to look into this but I am skeptical to the dissolved oxygen hypothesis. I also have never seen anyone posting any evidence whatsoever that dissolved oxygen levels would actually affect taste, so this is all anecdotal.

That said there might be other things that happens with a reboil, like a concentration of salts and minerals. This would be harder to predict since it would depend on the water source and kettle/boiling method.

AllanK said

If you notice I said it was pretty much a matter of preference.

I did notice, but the question whether the tea will be “flat” or whatever is not really a matter of preference, is it? That’s an empirical claim, if one choose to make it.

AllanK said

I think it may be a matter of just how sensitive your taste buds are. Some people may notice a difference, some may not.

Yes, that is entirely possible.
However, I think it would be interesting to know, as a start, if there is a chemical mechanism in place to facilitate such differences. What I am reacting to is that so many people (I am not pointing a finger at you here) make a lot of assumptions without any evidence. One such assumption is that “low oxygen content makes tea flat”. Okay, maybe so. But how does anyone know that? I would love to see some evidence.

AllanK said

I have been told it is bad to reheat the water by people who know more about tea than me, such as my local tea shop owner.

Oh wow, interesting…

TeaLife.HK said

This study states boiling at regular atmospheric pressure is not effective at removing dissolved oxygen.

In my experience, boiling hard water can leave a rather significant precipitate behind that makes the water ‘itchy’ on the swallow. That is definitely not desirable. IMO that is a bigger concern than the dissolved oxygen issue. You can aerate water simply by pouring from a height.

ZeroZen said

I mean you shouldn’t use hard water for good tea anyway. But you are right – IF you use hard water then the water itself after boiling it once gets quite foggy and you notice that the structure isn’t clear anymore.

But if you take the best source of water (soft, right ph level, not massive in amount of minerals etc.) then the reheating has no impact I would guess – and like you mentioned correctly if you pour water from a certain height into the pot it already collects oxygen again.

So I am really wondering what exactly might be the reason for this believe that reheated water (even if it is perfect water) is bad for your tea! Because if you read about the reason mentioned in certain tea books they might sound more esoteric than scientific like “The water loses its liveliness!”

And like “Tea for Steve” already mentioned: If it is boiled once where is the liveliness after being boiled? And what would make a difference being boiled twice?

TeaLife.HK said

The mystical purity of freshly boiled water?

Oddly my mom feels the same way about water for tea. She’s been a lifelong black tea (hongcha) drinker.

“This study states boiling at regular atmospheric pressure is not effective at removing dissolved oxygen.”

So what? What is the definition of “not effective” and how does it relate to tea? I don’t see that the study you linked say anything about the difference in dissolved oxygen content between boil 1 and boil 2 when reheating. There are so many assumptions being made that I have not seen any evidence for, including the basic assumption that dissolved oxygen levels (if the level really IS different after a re-boil, which I also have seen no evidence of) would actually affect the taste.

Dr Jim said

Our public water is pretty good, except for chlorine/fluoride. I’ve tried sping water, but couldn’t tell the difference. I use an electric kettle and always leave a cup or so behind so I don’t inadvertently run the kettle dry, which is bad for the heating element.

My feeling is that heating the water then letting it sit is likely to drive out the chlorine (natural form is a gas) so reboiling might help.

TeaLife.HK said

Boiling will remove some chlorine, but chloramine is trickier

Dr Jim said

Thanks for the tip. Turns out my water supply uses chloramine, so my letting it sit isn’t doing any good. :( On the up-side, I can’t tell the difference between my tap water and spring water, though I think I’m going to have to have another round of tests.

TeaLife.HK said

I’ve found my tap water in HK to perform better than Volvic. Nobody believes me! Lol. So yes I do believe you may not be able to tell the difference

Rasseru said

I recently did a small test and didn’t like the water with high mineral content. It had high sodium though which threw my dancong way off. I will try more too soon.

When I was younger I would always use fresh water every boil. I was very particular about my tea method and could taste a difference even without knowing any science.

I can’t taste a difference now but I’m also drinking varied teas compared to younger me drinking the same brand

Dr Jim said

I think that’s part of it. I do gong-fu most of the time, and every steep is different.

Rasseru said

i have been thinking about it, I used to like my tea very clear and hard, like glass. I didnt like it flat or milky.

The taste improved upon these preferences for harder tea with a fresh boil. 100% sure of that

ZeroZen said

Water itself has a huge impact on the taste for me but like I mentioned the type of water not really how much I boiled it. Here in Vienna we got one of the best drinking quality tab water in the World but it isn’t far from being great using it for tea.

I invested a lot of time, comparing and testing bottled and filtered water within the last couple of years. For me the absolute best turned out to be Lauretana from Italy. It is one of the softest and lightest water out there with a great ph level! For me personally there is not really some better than that until now – Icelandic Glacial is also amazing but to expansive and only available in small bottles here in my City!

Lauretana good…but if you wanna go all in and fancy, choose Fiuggi!

But hey… so do you think that our tap water here in Vienna is not acceptable?

ZeroZen said

Not really! It is good drinking quality but definitely not good for high quality tea. I mean if you’re having a cold and want to drink herbal tea then it is totally fine but not like I said for high quality tea. The problem with our water in Vienna at first is chalk. If you’re using porous clay pots it will totally ruin them after a certain time because a layer of chalk will build up and clog the natural flow. Beside that in many older buildings there is still an amount of lead into the water because of the old pipes. Then our water isn’t soft enough it may also not be hard as hell but far from good. But the best way is to test it yourself: Do a side by side tasting with the same tea, same amount of water and tea ratio and one with Vienna water and the other one with Lauretana. I sure you will be amazed by the outcome. With Lauretana a lot of the subtle notes can develop while they are suppressed by our tab water :)

TeaLife.HK said

I had a lot of trouble shaving in Wien…The water was surprisingly hard.

I actually asked about the dissolved oxygen factor on reddit in /r/chemistry and got some interesting replies that pretty much does away with the hypothesis that the oxygen content would be significantly reduced by successive re-boiling. Summarized like this: “there is no reason why the number of times boiled should have any effect on the solubility of oxygen.”

Also: “Boiled water is devoid of virtually all oxygen. By the time it’s boiled sufficiently to make tea, the amount of oxygen is essentially zero. The escaping steam carries the oxygen with it, and the solubility of oxygen in water at boiling temp is essentially zero. Boiling more than once will make no difference.”

Even more interesting, one individual argued that if anything a low dissolved oxygen content should be preferable for tea. Food for thought.

Here’s the thread:

I am terribly guilty of this crime. Not a kosher thing to do, I know, but sometimes I am too lazy to empty the old water out of my tea kettle. Not sure if I’d notice the difference though. I like to drink extra strong peasant quality Assam Tea. Garden fresh. High caffeine. It keeps me alert and fuels my day!

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