Is Boiling Water The Same In A Microwave Vs. A Kettle? 

A microwave sits on a countertop, next to a toaster and an electric tea kettle.

Does the method of boiling water affect the taste of tea due to a possible lack of re-aeration of oxygen in the water? I am guilty of boiling water in a microwave and boiling water in a kettle, forgetting about it, only to boil the water later for a cup of tea. Is there really a difference? Isn’t boiled water all the same? Is there a correlation to how water is boiled and the flat taste in a cup of tea?

Disclaimer: I am not a scientist by profession, nor do I have a scientific lab at my disposal to chemically analyse a cup of boiled water. I am a curious person who enjoys exploring the “whys” and “hows” of science and life!

A Study 

A woman wearing a ponytail is shown from behind. She is standing in front of a microwave, with a tea kettle sitting on the stove.

While researching the chemical makeup of boiled water for a previous blog, I came across a study that I found intriguing. The study delved into what causes the inconsistency of water temperature within a cup of microwaved water. Researchers at the University of Electronic Science & Technology of China published a study they conducted in 2020 regarding microwaved water. In summation, they concluded that the microwaved water is hotter on the top and sides of the liquid. They stated that the water was inconsistent in temperature throughout the cup of liquid due to the mechanics and physics of a microwave.

A Microwave And A Tea Kettle Explained 

The mechanics of how a microwave boils water is vastly different than how the heating elements of an electric tea kettle or stove burner boils water. The heating and boiling of water on the stove or in an electric kettle is conducted through a scientific process called convection. The heat is delivered externally to the bottom of the vessel, heating the water from the bottom of the vessel upwards. As the water boils, the less dense hot water rises to the top of the pot or kettle and the more dense cooler water remaining at the bottom of the vessel then begins to heat up.

In a microwave the heating elements are electric fields. When the microwave is in use, the electric fields heat from all directions, heating up a cup of water from all sides. The electric fields will heat up the top of a cup of water and the sides of the cup before they actually heat up the inside middle of the cup of water. In essence, when a cup of water appears to be boiling in a microwave, it may only be the top surface area that has actually reached a boiling temperature. The inside middle of the cup of water may still be below a boiling temperature.

A Boiled Cup Of Water 

Boiled water still has oxygen and hydrogen in the cup. During the boiling process, the bonds holding the hydrogen and oxygen molecules together are broken. The hydrogen and oxygen molecules turn to a gas. The longer water is boiled, the more of the liquid turns to a gas form, and eventually can be completely boiled so that there is no liquid left. In addition, during the process of boiling water, oxygen is reintroduced to the water via what is called re-aeration. Simply stated, oxygen is dissolved into the water from the surface air when the water is in a turbulent state. This aeration of water is what causes a great cup of tea. Without the aeration of boiling water, the water can be flat, thus creating a dull, and lifeless cup of tea.

A Hypothesis 

Three different white cups are filled half-way with tea. They are labeled Cups 1-3. Each cup of tea has a slightly different liquor. Behind the cups, the wet leaves are also shown.

The study made me think of boiled water and the three basic methods of obtaining hot water for tea. The basic three ways to obtain boiling water for tea include utilizing a microwave, or a kettle/pot on top of a heating element, and lastly, re-boiled water from a tea kettle/pot previously left to sit for hours. Does microwaved water have decreased re-aerated oxygen levels due to inconsistent temperatures within the cup, creating a flat cup of tea similar to previously boiled water that has been left for hours, compared to freshly boiled water in a kettle?

My hypothesis was to see if I noticed a difference in the taste of tea due to the method of boiling water affecting the possible reaeration of oxygen in water. I believe that I will not notice a taste difference in tea in which the water had been boiled in a microwave versus boiled in a tea kettle. I do, however, think that I will notice a difference in the taste of tea using water that was previously boiled, left to cool for 7 hours and then re-boiled. I think the tea made from previously boiled water will taste flat, have a thin mouthfeel and have little flavor profile.

An experiment 

Three different white cups are filled half-way with tea. They are labeled Cups 1-3. Each cup of tea has a slightly different liquor.

The experiment was conducted using filtered tap water that I obtained from a countertop filtration system. I was very careful to keep my confounding errors (Type I and Type II errors to a minimum). I used tepid water that had not been previously boiled, in the microwave and in one electric tea kettle. In another electric tea kettle, I re-boiled previously boiled water that had been left to cool for 7 hours. I used the same sized tasting cups to steep the tea. I boiled the tea at the same time and steeped the tea concurrently for 3 minutes. I measured out 1.3 grams of tea and used 2 ounces of water. I used a decreased amount of water and loose leaf tea due to a limited supply of tea. I wanted to use the same merchant's tea from www.lotatea.com, and the same batch of tea to keep everything as consistent as possible.

I steeped Margaret’s Hope Darjeeling in all three cups. Margaret's Hope is a second flush Darjeeling with a heavenly muscatel and orchid aroma, a wonderful muscatel grape taste and mild astringency. It is a complex tea with numerous flavor and aroma notes. It is called the champagne of teas, and is purportedly what Queen Elizabeth II of England enjoys during her afternoon tea time. It is one of my favorite teas. I steep this tea when I am in a contemplative, quiet frame of mind, because it is when I am quiet and still that I can truly experience and enjoy all the complexities that this tea has to offer! My reasoning in using this complex tea was that if any of the water caused a flat flavor profile, hopefully the tea would be altered enough to notice the flat taste.

A Conclusion

I did notice a difference in all three cups of Darjeeling! The Darjeeling that was steeped in the tea kettle using freshly steeped tea (cup #1) had a pronounced aroma of orchids, grapes and a sweet floral note. The color of the liqour was a light amber. The flavor was divine; the tea had a muscatel taste with just the right amount of astringency hitting the side of the mouth but not causing an extreme pucker of the mouth. To me…. This was an ideal cup of Darjeeling.

The next Darjeeling that I sampled was the tea steeped in re-boiled water. The color of the liquor in cup #2 was a bit darker and there was no aroma. I tasted the tea and it had a thicker mouthfeel than cup #1, and it had a sharp unpleasant taste without the astringency. It also did not have a muscatel taste. Actually, the only taste I detected was a sharp, nondescript taste.

Cup #3 was steeped with water that had been boiled in the microwave. The liqour was darker than the other two cups of Darjeeling. It had a faint orchid aroma. It had a thick mouthfeel, and little astringency. It tasted like a flat cup of stale black tea with no complex flavor profiles. 

Afterthoughts.

I enjoyed conducting my tea experiment and was surprised to find that my three cups of Darjeeling tea did not taste the same. There could be several reasons for this. One of the reasons could be that I over-boiled the microwave water to make sure the middle of the water reached a boiling temperature, thus causing the Darjeeling to be inadvertently over-steeped. Secondly, the microwaved and re-boiled water may not have successfully re-aerated. To me, all boiled water, being equal in water type, is not the same boiled water. I noticed a difference in my cups of tea.

The premise of this blog was two fold: to foster and encourage curious minds and to show how easy it is to experiment and play with tea.

Keep learning, keep being curious, keep drinking tea,

Leslie

References:

Arumugam, Nadia.Food Explainer: Why does Microwaving Water Result in Such Lousy Tea?Slate, June 4, 2013.

Connellan, Shannon.The science that proves making your tea in the microwave is a truly appalling act.Mashable, August 5, 2020.

University of Electronic Science & Technology of China. Multiphysics analysis for unusual heat convection in microwave heating liquid.AIP publishing, August 4, 2020.

About The Author

A photo of Leslie on the patio wearing a pink cardiganLeslie Sundberg is a World Tea Academy Certified Tea Specialist, a World Tea Academy Apprentice Tea Sommelier, a Specialty Tea Institute Level IV trained Tea Specialist, and a Tea and Business Etiquette Specialist. On any given day, Leslie can be found teaching, speaking or sharing in the joys of a cup of tea.  No matter what Leslie is doing or where she is, one thing remains constant: 4:00 in the afternoon is tea time!

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