---
title: Why Is Microwave Tea Bad?
description: "Microwaving water for tea makes it taste bad, for unknown reasons. Is it a lack of bubbles? Lingering CO<sub>2</sub>? Comments and proposed experiments."
created: 2022-03-22
modified: 2025-12-24
thumbnail: /static/img/triple-question-mark.png
thumbnail-text: "Three superimposed tilted question marks sharing the same dot as a symbol of severe confusion, beyond a single question mark."
status: finished
confidence: possible
importance: 1
css-extension: dropcaps-de-zs
...

<div class="abstract">
> Why does microwaved tea taste bad?
> I discovered this in college, and many tea-drinkers agree: heating water in a microwave somehow makes tea taste worse!
>
> There is no obvious *chemical* difference between H~2~0 heated on an electric heating coil in a tea kettle and one heated by microwaves---so how is this possible?
>
> I suggest that it is not a chemical difference so much as a *physical* difference, like texture, which can affect taste a lot.
> Specifically, normal tea has lots of boiling bubbles from uneven heating inside metal or ceramic containers, while microwave heating of glass containers produces (dangerously superheated) even heating and no bubbles or boiling.
>
> If so, then the bad taste of microwave tea may be fixable by adding rough surfaces or injecting air or active stirring.
</div>

In college, my dorm room had no access to a stove, but I was right by the break room with a microwave, so for convenience, I would make my tea by using it to boil water in a [glass travel mug](https://www.trendglas-jena.com/en/spd/220105/Mug-ZYCLO-G "trendglas: Mug ZYCLO G")[^mug-review] with tea leaves.
But the tea was never as good as back home where I had a regular stove-top kettle: it always tasted wrong, 'flat' or 'hollow' like decaffeinated tea.

[^mug-review]: I don't recommend trendglas's Mug ZYCLO G.

    The volume was too small, the cute rounded handle meant that my finger was always slipping upwards to touch the thin glass itself (uncomfortable and risking burns), and the glass was worrisomely dangerous for travel (I was always terrified of it shattering in my luggage, and eventually one day it shattered on its own).

    After it broke, for travel I moved to [Finum tea filters](https://www.amazon.com/Finum-Brewing-Basket-medium-black/dp/B000I68NCS/) combined with whatever cup or mug I could find locally.
    In 2025 I upgraded to the ["LocknLock Metro Tea Mug"](https://www.amazon.com/dp/B0C6QHMLFF) which has been working well and avoids all the problems of the trendglas mug.

I was never sure why.
I was using the same tea, and the glass travel mug didn't seem to be the problem, because regular kettle water worked fine.
Was the college water bad in a way I couldn't taste?
Or when I set the microwave, did I heat it up too much? Did it steep too long/too short?
Maybe I needed to use a low-power setting for some reason...?
I couldn't fix it and there was no convenient stove, so I eventually decided to just buy an electric kettle.

However, I never forgot it, because I kept wondering *why* the microwave approach didn't work.
Curious, I later searched and found I was far from the first person to notice this, and in fact, tea drinkers universally agree that microwaving water for tea instead of using a kettle (whether electric or not) results in worse-tasting tea, regardless.
So it didn't seem to be anything about my setup, but a law of nature about water in a microwave.
But why?
(I have not done a [blinded randomized test](/water "'Self-Blinded Mineral Water Taste Test', Gwern 2017") like I have of mineral water types, because I'm wary of trying to physically randomize cups of boiling water, so let's take this as a given for now.)

# What Chemical Difference?

It's puzzling that the method of heating the water should make any difference to the subsequent tea, since no matter how you get to 100℃, it ought to be the same boiling H~2~O.
It cannot add or subtract any chemicals, or in any way be physically different---can it?

Online speculation sometimes suggests "deoxygenation" as the chemical issue, as the lower oxygen capacity of hot water is well-known.
I'm not sure how this would work.
Cold moving water doesn't contain much dissolved oxygen to begin with (apparently on the order of only 10 parts per million), and hot still water would contain much less.
Does oxygen gas make any taste difference at all at such low levels?
And it's not obvious that the route of heating should lead to any difference in final oxygen gas content---much less make a *huge* difference much later in the steeped tea that could explain this.

# Physics of Taste

A more plausible mechanism involves the difference you can literally *see*: the bubbles during boiling.
Microwaved water, because it heats the entire volume of water evenly compared to a hot heating element at the bottom of the kettle, will have many fewer bubbles from the [boiling](!W); an example of this is the dangerous [superheating](!W) effect where a container of boiling-temperature water may be still until you disturb it slightly, at which point it ['explodes'](!W "Flash evaporation") boiling-hot water/steam at you.^[I observed this several times with my glass travel mug, and that was part of why I began putting the tea leaves in before rather than after: tea leaves provided extensive nucleation sites.]
The boil can't happen without 'nucleation' sites to form the seed bubbles.

A striking example of how important nucleation sites can be is the famous [Diet Coke and Mentos eruption](!W) effect---it has nothing to do with any chemistry of 'acidic Diet Coke reacting with basic Mentos' or anything like that. The Mentos effect is solely driven by the physical fact that a Mentos mint turns out to have thousands of seed bubbles trapped in tiny cracks, which lets the pressurized CO~2~ gas dissolved in the Diet Coke liquid instantly boil out.
Other examples come from food science, where it is well-known that the surface area and texture of food particles are far more important to how they *taste* than their total volume or mass, because we perceive by molecules docking in taste buds on the tongue & smell receptors in the nose, and the actual mass is irrelevant; so one can [engineer low-calorie sugar](https://www.newyorker.com/magazine/2020/09/28/the-race-to-redesign-sugar "The Race to Redesign Sugar: Forget artificial sweeteners. Researchers are now developing new forms of real sugar, to deliver sweetness with fewer calories. But tricking our biology is no easy feat.") by making sugar particles with a high surface area and low total mass, which will fit in the same number of sweet taste receptors as the original high-calorie formulation with large heavy sugar particles.
Bubbles are even critical to [water aeration](!W "Aerated water"), as [fine bubbles](https://en.wikipedia.org/wiki/Water_aeration#Fine_bubble_aeration) maximize surface area & time-in-water.

## Effervescent-Tasting

So, the problem with microwave water vs boiling water might be the boiling *bubbles themselves*!
A lack of bubbles, however small they are, may destroy the flavor.
It might be the equivalent of wearing nose-clips and then being surprised how hard it is to distinguish potatoes from strawberries, because the aroma is gone.
Or perhaps the effervescence is pushing more flavor into the tongue's taste buds.

# Microwave for Bubbles

This could be tested by finding a container so rough that microwaved water boils normally

Conceptually similar to a [boiling chip](!W), like perhaps a small rough object at the bottom?
But not Mentos mints or [tapioca pearls](!W) since they would dissolve & change flavor/texture, but something similar).
Perhaps by injecting lots of small bubbles into microwaved water (something like an [atomizer](!W "Spray nozzle") or [aerosolizer](!W "Aerosol spray dispenser").

# CO~2~?

Finally, one possible chemical explanation, related to the aeration thesis, is that there *is* a perceivable chemical difference from the boiling due not to oxygen---but [CO~2~](!W).
CO~2~ in water is acidic and taste-able (see: [carbonated water](!W) for soda), and the boiling process in a kettle, by generating more bubbles, [degasses](!W "Degassing") more CO~2~, and [may reduce the acidity](https://www.reddit.com/r/chemistry/comments/ywji3k/ph_of_water_boiled_in_steel_vs_microwaved/ "‘pH of water boiled in steel vs microwaved?’, Melodic_Currency_822 2022") by a substantial amount.

Hence, increasing bubbles in a microwaved tea might improve the flavor, but not because of the bubbles's mere physical presence per se, but because those bubbles removed more CO~2~ than normal.

How would we test this ambiguity?

#. One possibility would be to let microwave tea sit for a few minutes after microwaving, to allow for further offgassing.

    (We would have to overheat both kettle & microwave water to ensure that they cool down to an appropriate steeping temperature.)
#. Better yet, we could prepare two microwave mugs, and *reheat* the first mug after letting it sit for a few minutes; while they will be at the same final temperature and have similar bubble aeration, the first one should offgas more CO~2~ than the second one, and taste better.
#. We could try shaking heated water in a sealed container with as little air in it as possible; that lets out little CO~2~ but increases the physical bubbles.
#. We could also use test strips and home CO~2~ kits to:

    - check the microwave water for pH equality with the kettle water, and
    - spike the kettle water with CO~2~ (or [citric acid](!W)) until it matches the microwave; both should eliminate the blinded taste difference.

    (The test strips would help double-check that the different treatments changed the acidity in the expected directions.)