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Reboiling water


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#1 Fat Guy

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Posted 21 October 2011 - 08:57 PM

I have one of those Russell Hobbs electric kettles. I fill it part way with water, run it until it boils, and pour some of the water into a mug for tea. When I go to boil more water, I pour out the remaining water, refill the kettle, and go again.

Several other people I know, by contrast, leave the water in the kettle and boil it again.

I somehow feel that reboiled water is going to be somehow inferior. Is this completely in my imagination or is it for real?

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#2 Hassouni

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Posted 21 October 2011 - 09:07 PM

I think it's your imagination. I do this all the time. The water here isn't good enough for me to be fastidious about it

Edited by Hassouni, 21 October 2011 - 09:08 PM.


#3 ScoopKW

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Posted 21 October 2011 - 09:16 PM

I would give my left [censored] to have water as good as yours, Steve. Reboil away!
Who cares how time advances? I am drinking ale today. -- Edgar Allan Poe

#4 KD1191

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Posted 21 October 2011 - 09:49 PM

The level of oxygen in the water is a key element in making tea, the higher the better. Thus, freshly drawn water will produce a better cup.
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#5 Hassouni

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Posted 21 October 2011 - 09:56 PM

Isn't the level of oxygen in water constant, H2O and all that? I'm not a chemist, I'm actually rather curious about this

#6 Ashen

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Posted 21 October 2011 - 10:08 PM

I don't think they are talking about the molecular oxygen but the dissolved gass oxygen in the water. Water is fairly soluable to gasses, and usually holds oxygen , nitrogen , carbon dioxide and other gasses in Solution. When boiled this gasses end up escaping .

Bottled water often uses this ability of water to contain gasses in solution by adding ozone for taste.
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#7 ScoopKW

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Posted 21 October 2011 - 10:26 PM

Just shake the hell out of the kettle before reboiling. Or add more water. Or zap it with a stone and O2 tank borrowed from your beer-making equipment. Any of those will return dissolved oxygen into the mix.

No need to pour perfectly good water down the drain. If anything, I'd pour that water into the ice-cube trays for making drinks. Lack of dissolved O2 is a bonus in those situations.
Who cares how time advances? I am drinking ale today. -- Edgar Allan Poe

#8 Wholemeal Crank

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Posted 21 October 2011 - 10:53 PM

I keep my kettle at the right heat until I'm done with the tea session, and for most of my infusions that means it reboils a bit every few minutes, as the kettle keeps the temperature up around 205 or so. I've never considered dumping the water during a session.

#9 slkinsey

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Posted 22 October 2011 - 06:11 AM

Guess how much dissolved oxygen there is in water at 100C? If you guessed "none" give yourself a prize! Solubility of oxygen in 100C water is 0 mg/l.

The only reason to not re-boil water is if you have high levels of non-volatile substances in your water, e;g;, if you have hard water or if you're concerned that you might have mercury or lead in the water. Reboiling this kind of water would have the effect of increasing the concentration of these non-volatile substances. Although I should point out that the effect would be negligible if we're talking about a kettle where there is very little evaporation.

Luckily you live in a city that is known for having some of the best, if not the best quality municipal water in the country. So don't sweat it.
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#10 dcarch

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Posted 22 October 2011 - 07:04 AM

I agree with slkinsey. That's the whole science there.

It really boils down :biggrin: to convenience.

For me, I microwave as much as water as I need each time. I don't reboil water in a kettle.

Why? Sometime ago I discovered a cock roach in the water, after I drank the tea I made with the reboiled water.

Actually, the tea was not bad at all, as I recall.

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Edited by dcarch, 22 October 2011 - 07:05 AM.


#11 gfweb

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Posted 22 October 2011 - 07:07 AM

Dissolved minerals will be a little higher in reboiled tap water

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#12 Dianabanana

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Posted 22 October 2011 - 08:55 AM

Guess how much dissolved oxygen there is in water at 100C? If you guessed "none" give yourself a prize! Solubility of oxygen in 100C water is 0 mg/l.


Oh, this is wonderful! Reboiling water is a subject of hot debate in our house. I can't wait to whip out this fact. VICTORY IS MINE!

#13 Hassouni

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Posted 22 October 2011 - 09:12 AM

Guess how much dissolved oxygen there is in water at 100C? If you guessed "none" give yourself a prize! Solubility of oxygen in 100C water is 0 mg/l.


Does it slowly lose dissolved oxygen as it heats up and by the time it hits boiling there's none left, or does it start shedding oxygen at the boiling point?

#14 Will

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Posted 22 October 2011 - 10:46 AM

I know folks on both sides of this camp. I think it's also different if the kettle shuts off just at the moment it hits a boil vs. if you're leaving it at a boil for minutes at a time. A lot of people do feel that letting the water boil too long takes out too much oxygen; I'm not enough of a scientist to prove or disprove that claim. I try to split the difference - I'll reboil (just the the boil) 1-2 times with the same water, and then I'll usually top it off with fresh water.

#15 slkinsey

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Posted 22 October 2011 - 10:58 AM


Guess how much dissolved oxygen there is in water at 100C? If you guessed "none" give yourself a prize! Solubility of oxygen in 100C water is 0 mg/l.

Does it slowly lose dissolved oxygen as it heats up and by the time it hits boiling there's none left, or does it start shedding oxygen at the boiling point?

The solubility of oxygen in water doesn't quite decline linearly as temperature rises, but it might as well. It's right around 14.5 mg/l at 0C, right around 9 mg/l at 20C (room temperature), right around 6.5 mg/l at 40 C, right around 5 mg/l at 60C, right around 3 mg/l at 80C and 0 mg/l at 100C. I should hasten to point out that once water undergoes the phase shift from liquid to solid at 0C, the solubility of dissolved gas plummets to zero.

Effectively what this tells you is that there is very little dissolved oxygen in any water that might be perceived as "hot."
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#16 slkinsey

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Posted 22 October 2011 - 12:11 PM

I know folks on both sides of this camp. I think it's also different if the kettle shuts off just at the moment it hits a boil vs. if you're leaving it at a boil for minutes at a time. A lot of people do feel that letting the water boil too long takes out too much oxygen; I'm not enough of a scientist to prove or disprove that claim.

These people are wrong. The water is continually losing dissolved oxygen as it approaches the boil (this is all the bubbles that come out of the water before it actually reaches the boil) and once it does reach the boil the amount of dissolved oxygen in the water is effectively zero. Even below the boil at 95C, you're talking about around 1 mg/l of dissolved oxygen. Consider that a glass of cold water has around ten times more dissolved oxygen than that. What this tells us is that the boiling the water for only a few seconds or starting with fresh water or even heating the water only to under the boil will have no effect that is attributable the concentration of dissolved gas in the water.
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#17 Chris Hennes

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Posted 22 October 2011 - 12:16 PM

How much dissolved oxygen does it take to affect the taste of coffee or tea?

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#18 dcarch

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Posted 22 October 2011 - 12:17 PM

There is also nitrogen, chloriine, etc in water.

You can make heavy water.

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#19 andiesenji

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Posted 22 October 2011 - 01:01 PM

How much dissolved oxygen does it take to affect the taste of coffee or tea?



For most people this is not much of a factor in brewing tea or coffee. I'm considered a "supertaster" as I had (as part of a test group at a university) my tongue treated with a dye and several impressions were taken of it.

I have brewed the exact same tea, carefully weighing it exactly, in water from a water boiler (Zojirushi) from my In-Sink-Eeator hot water dispenser, and from a teakettle with freshly drawn well water brought to a rolling boil and dispensed immediately.

each batch of tea was brewed exactly the same amount of time and immediately decanted into a separate pot to avoid any chance of overbrewing.

My friends who helped with this totally unscientific "test" could not discern any difference in the taste of the tea (an Assam single estate Hazelbank FTGFOPT) with or without milk and/or sugar, and neither could I.

In my opinion it is possible that people who have heavily treated water may notice a difference but in some cases it might be advantageous to prolong or repeat the boil because some particulate matter that could possibly affect the tea would precipitate out.

Some friends who only "discovered" tea a few years ago have done extensive traveling and tasting in many tea-growing areas (currently in Africa) and have stories about drinking tea at almost ever altitude available to the casual traveler, including an underwater restaurant in Dubai.
They said that even though some people complained about the tea made with water boiled at a lower temperature when they were in the highlands in Sri Lanka, they did not note any difference in the taste of the tea and thought it just as good as that brewed at the place they stayed in Amanwella.

They have come in contact with more than a few people that they consider tea snobs and who offered them advice that they thought was ridiculous. They don't advertise that they are both doctors and know a great deal more than most strangers credit them with.

Edited by andiesenji, 22 October 2011 - 01:02 PM.

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#20 Chris Hennes

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Posted 22 October 2011 - 01:09 PM

So the upshot is that if Steven's water is inferior the second time around, it can't possibly have anything to do with dissolved oxygen, right? The only real possibility is if it has accumulated something from the pot itself, and using fresh water minimizes the effect?

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#21 nickrey

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Posted 22 October 2011 - 02:04 PM

I'd suggest that any taste difference is probably the effect of multiple incursions of kettle scale into the water. Let's try the obvious answer before blaming questionable suspects such as dissolved oxygen.

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#22 dcarch

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Posted 22 October 2011 - 02:08 PM

Has anyone tasted distilled water?

100% pure distilled water tastes very funny.

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#23 Will

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Posted 22 October 2011 - 02:18 PM

Has anyone tasted distilled water?

100% pure distilled water tastes very funny.

Yeah - distilled and RO water have an unpleasant taste (or lack of taste, really), and I find them a little rough on the throat. For most tea brewing, a spring water with low TDS is ideal, or water filtered with a good multistage carbon filter. You need some mineral content, but not too much.

However, I think minerals will be more concentrated, rather than less, when boiling water for a long time.

I don't know what causes water that's been boiled for a long time to be a bit more "flat", but it's a very subtle difference at any rate. I wouldn't think additional scale would make the water or tea more flat - in fact, in some cases, it's desirable.

Edited by Will, 22 October 2011 - 02:18 PM.


#24 andiesenji

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Posted 22 October 2011 - 03:23 PM

So the upshot is that if Steven's water is inferior the second time around, it can't possibly have anything to do with dissolved oxygen, right? The only real possibility is if it has accumulated something from the pot itself, and using fresh water minimizes the effect?


I don't think Steven's water is at all inferior and that's not what I intended to say. I have a deep well that produces excellent water with a lot of mineral content but there is an inline filter right off the wellhead that removes a lot of it.
I have friends who recover rain water which is held in closed cisterns (and filtered before it goes into the house.
I have other friends who are on municipal water lines and we all brew tea from water kept at brewing temp in a water boiler. I happen to have a Zojirushi as does the friend with the cistern and the other friend has a different brand but it works the same way. Almost everyone I know who drinks tea daily has one of these or an instant water heater. A few have kettles, either electric or stovetop. Only the ones with very small kettles fill with fresh water each time.

My point is that somewhere in the more recent history of tea, someone who impressed other people with his expertise made much of the "necessity" of using fresh water, newly boiled, to brew tea. For people with running water in the house this was not a hardship, but consider folks that had to haul water from a well or other sources.
It was not feasible to throw out perfectly good water and start over with a fresh batch, so usually it was just add more water to the kettle if needed or reboil what was in it. And I am quite sure than anyone insisting on absolutely fresh water would not have been looked on with kindness.

At one time I did believe that fresh water, freshly boils was best but that was many years ago. I met someone who had had a lifetime of experience with tea and he told me that laying down strict rules for brewing tea was "loblolly thinking!" - I tried to look it up but was unsuccessful then eventually learned it meant "porridge for brains." (long before the internet).

Each individual can choose how they like to brew their tea. There are no hard and fast rules. If one enjoys tea brewed a certain way they should stick to it or try other methods to see if that suits them better.

In my posts I am referring to the most commonly available teas, black, oolong, green, flavored etc., but I would hazard a guess that the more delicate white teas and rare greens would benefit from filtered, freshly heated but not boiled water.

Edited by andiesenji, 22 October 2011 - 03:27 PM.

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#25 slkinsey

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Posted 22 October 2011 - 08:51 PM

So the upshot is that if Steven's water is inferior the second time around, it can't possibly have anything to do with dissolved oxygen, right? The only real possibility is if it has accumulated something from the pot itself, and using fresh water minimizes the effect?

I don't think that's the upshot at all. I think the upshot is not that Steven's water actually is inferior the second time around. I think what he's saying is that he doesn't actually reboil water because he has the idea that it would be inferior the second time around.

New York City tap water is better quality than most bottled water, especially if you have removed the small amount of chlorine used (either by filtration or by degassing through boiling). More to the point, it is naturally very soft water. So it's pretty much impossible that his kettle would concentrate enough dissolved solids to produce a negative taste effect unless he never ever emptied the kettle and rinsed it out. Even if he always only used half of the water and always replenished the kettle without ever pouring out all the water, it would take many, many kettles of half-reboiled water before the nonvolatile substances approached the concentrations that many parts of the country consider normal.
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#26 andiesenji

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Posted 23 October 2011 - 09:57 AM


So the upshot is that if Steven's water is inferior the second time around, it can't possibly have anything to do with dissolved oxygen, right? The only real possibility is if it has accumulated something from the pot itself, and using fresh water minimizes the effect?

I don't think that's the upshot at all. I think the upshot is not that Steven's water actually is inferior the second time around. I think what he's saying is that he doesn't actually reboil water because he has the idea that it would be inferior the second time around.

New York City tap water is better quality than most bottled water, especially if you have removed the small amount of chlorine used (either by filtration or by degassing through boiling). More to the point, it is naturally very soft water. So it's pretty much impossible that his kettle would concentrate enough dissolved solids to produce a negative taste effect unless he never ever emptied the kettle and rinsed it out. Even if he always only used half of the water and always replenished the kettle without ever pouring out all the water, it would take many, many kettles of half-reboiled water before the nonvolatile substances approached the concentrations that many parts of the country consider normal.


Well said! - or written!
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#27 nickrey

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Posted 23 October 2011 - 01:08 PM

Seems the water is great at the source and in the intermediate delivery system. There must be some old plumbing though: even the water board acknowledges this is a source of contamination. This stuff gets into kettles and creates scale. See my comment above.

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#28 slkinsey

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Posted 23 October 2011 - 07:21 PM

Scale comes from "hardness" in the water -- i.e., calcium carbonate, calcium sulfate, and magnesium hydroxide. This is not something that is going to be picked up out of old plumbing. Yes, I suppose if Steven always replenished a half-full kettle and never ever emptied it, it would eventually concentrate enough minerals to scale. But this is unlikely to happen. Most of the time with ordinary use of a kettle it is emptied every so often. The point is that there's not much use of emptying it every time, because replenishing the kettle rather than filling it with fresh water isn't going to make much difference with NYC tap water at least for 5-10 replenishments.
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#29 Fat Guy

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Posted 23 October 2011 - 07:24 PM

If slkinsey is right, and it sounds like he is, then I have wasted about 50 million gallons of water in the past couple of decades.

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#30 gfweb

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Posted 23 October 2011 - 07:43 PM

You and my wife. She insists that once-boiled water is no good. This despite tons of science education and my own rational discussions invoking past chemistry courses and common sense.