Microwave vs Kettle for Tea

Many people like to start their day with a hot cup of tea. If you're a fan of tea, then you probably make it a certain way. Some people heat water in a microwave. Others use a tea kettle on a stovetop to heat water.  

Is it better to use a microwave oven or kettle when heating water for tea? Using a tea kettle is better since the water is heated evenly.

Heating Water in a Microwave

A microwave oven heats foods and liquids with microwaves, one type of wave on the electromagnetic spectrum. These waves produce constantly changing magnetic and electric fields. For this discussion, our focus is on the changing electric fields.

Main parts of a microwave oven

• Magnetron – a vacuum tube that generates energy that heats food
• Waveguide – inside the wall; directs energy into the food
• Chamber – holds food and safely contains microwave radiation

How a microwave oven works

• When the start button is pressed on the microwave, the magnetron converts the electricity from the electrical outlet into microwaves.
• These waves go through a hollow metal tube called a waveguide into the cooking chamber.
• The microwaves bounce off the metal walls of the oven’s food chamber.
• When the waves reach the food, they are absorbed by their water content (in this case, the water is heated). This absorption makes the molecules move back and forth, creating the heat that cooks the food.
• When these microwaves come into the chamber, they go all over the inside compartment. This results in the liquid at the top of the mug being hotter than the water at the bottom. Also, the water at the top does not drop to the bottom.

Zhao et al. found that the electric fields were unevenly distributed when using a microwave to heat a liquid. This means there can be hot spots anywhere in the liquid.

Zhao referred to this as “unusual convection.” This occurrence keeps the liquid always heated at the top, and the water at the top does not drop to the bottom. This resulted in uneven water temperature.

While you can stir the water, it may not be at the optimal temperature. As you’ll see in the next section, water temperature is essential when brewing tea.

How Water is Heated in a Kettle

Water heated in a kettle is heated by convection. Convection occurs when there is a difference in temperature between two parts of a liquid or gas.

Heat energy is always transferred from an area with a higher temperature to a lower temperature.  

The liquid is evenly heated when a kettle is used to boil water.

How convection works

• The heat comes from the bottom when a kettle of water is heated on a stove.
• The molecules in the warmer liquid move fast and spread far apart. They occupy a large volume which results in a decreased density. The warmer liquid rises from the bottom and transfers heat energy to the other molecules.
• As the liquid cools off, the molecules slow down and come closer together. They occupy less volume resulting in an increased density. The cooler molecules sink back down through the fluid.
• When they reach the bottom of the liquid, the cycle starts over again. This results in a uniform water temperature throughout the container.

Ideal Water Temperature for Brewing Tea

When the correct water temperature is used for brewing tea, the best tea flavors are brought out. For example, the tannins will be under-extracted if the water is too cold for green and black tea. The tea won’t have the full flavor it was designed to create.

If the water is too hot, the tea will be astringent (dry, bitter flavor), and the aromatic compounds will be decreased because the tannins were over-extracted. This is especially problematic in brewing white and green teas. The bitter taste can easily overwhelm the other flavors in the tea.

There are different temperature ranges for brewing each type of tea. The water temperatures for many teas fall below the boiling point of water (212°F).

Suggestions for starting points for water temperature for various teas are given in the table below. The optimal brewing temperature depends upon personal taste. A kitchen thermometer is helpful to gauge the tea’s temperature.

Sources: * https://redblossomtea.com/pages/brewing-guide

** https://www.silkroadteas.com/how-to-brew-loose-leaf-tea/

If a tea kettle is used, you’ll know when the water has reached the boiling point. After the water has just begun to boil, let it cool to the desired temperature.

If you prefer, add bottled or filtered water to cool it down. Another alternative is to cool the water down by pouring it from one bowl or mug to another.

Best Water to Brew Tea

What is EGCG?

Green and black tea contain Epigallocatechin Gallate (EGCG) (green tea has much more).  EGCG is an antioxidant that prevents free radical damage to cells. (Free radicals are known to contribute to chronic health problems.) EGCG is also known to inhibit cellular oxidation, which can lead to tissue and cell damage. 

Does water type affect the amount of EGCG in the tea?

Frank et al., researchers at Cornell University, tested different types of water used to brew tea to determine if they affected the flavor and the amount of Epigallocatechin Gallate (EGCG) in the tea.

Three types of water were used: bottled, tap, and deionized. The same temperatures, vessel, time, and water-to-leaf ratios were used.

The results showed the type of water used to make black tea did not affect EGCG levels. However, green tea made with either bottled or deionized water contained twice the amount of EGCG than tea made with tap water.

Water Type for the Highest Concentration of EGCG

Does water type affect the flavor of black and green teas?

In addition to EGCG testing, a panel of testers was asked to evaluate black and green tea made with bottled, deionized, and tap water. After tasting black tea, they were asked to assess various flavor attributes.

They thought black tea tasted the same, regardless of the type of water used, except for one attribute. They shared that when tap water was used for brewing, it was an earthier tasting tea.

However, this did not affect whether they liked the tea or not. The researchers concluded water might not be an important factor in whether or not someone likes black tea.

The panelists preferred green tea brewed with tap water over bottled and deionized water. One reason was that the tea brewed with tap water was much less bitter than the other two types of water. 

If you use hard water to make your tea, clean your tea kettle frequently to avoid limescale build-up.

Panelist Results – Water Type for Best Flavor

Making Water for Tea in a Microwave

One advantage that makes the microwave appealing is that it heats the water faster than in a kettle.

Not everyone has a tea kettle or, if they do, want to use it every time they make tea. If this is the case, perhaps experimenting with various times will enhance the flavors when using a microwave oven.

As we discussed, the water temperature is an important issue for brewing tea. To heat water in a microwave to a specific temperature, you'll have to determine the time needed to reach that temperature. Here are a few tips.

• Use the same mug, brand of teabags or loose tea, and type and amount of water.
• Microwave the water for different lengths of time – 90 seconds, 110 seconds, etc.
• When the water is ready, stir the water and take the temperature with a kitchen thermometer.
• Start with the temperature in the table above for the kind of tea you are brewing, and then adjust if necessary.

Once you get the temperature sorted out, you can prepare tea using bottled, deionized, and tap water and decide which one you prefer for brewing your tea.

Final Thoughts

There is a surprising amount of debate about whether it is better to use a microwave or kettle to heat water for tea.

Microwave ovens produce water that is heated unevenly. However, with some experimentation, you can determine the amount of time to microwave water to attain a specific temperature.

The other advantage of a microwave is that it takes less time to heat water. If every minute in the morning counts, you might gravitate towards using a microwave to prepare your hot tea.

A kettle heats the water evenly, and you will be alerted when the water starts to boil. Using a kettle will take slightly more time to prepare the water.

If you don’t have a kettle and don’t want to use the microwave, you can boil water in a pot or saucepan on the stove. If you are in the market for a saucepan for your induction cooktop, check out this article for reviews.