Why Not Recommend To Use A Vacuum Flask To Steep Tea?

Last Updated on 12/09/2020 by Desmond

To make a perfect pot of tea needs to take some effort. For some tea lovers, they like to use a vacuum flask to steep tea. Put the leaves in the flask directly, fill in hot water, and it can offer hot tea all day in the office or outdoor. It seems to be an intelligent and convenient way to enjoy tea.

But is it really a good way?

The senior tea loves are opposing this way at all, also am I. Even a rumor that said to use a vacuum flask to make tea may cause heavy metal poisoning. What makes them saying like this?

Not recommend using a vacuum flask to steep tea for a long time
Not recommend using a vacuum flask to steep tea for a long time

Why Not Recommend To Use A Vacuum Flask To Steep Tea

Affecting Flavor

We know that each tea has a suitable brewing time to get the best flavor. Like green tea typically needs just a few seconds, and dark tea costs more, even ok for cooking.

Using a vacuum flask to make tea will let the leaves be stewed for a long time. The components like tea polyphenol, tannin, and caffeine in tea will be extracted persistently and make a high concentration in the infusion. These components are bitter and astringent, and a high concentration will make the tea taste worst. The ones which bring sweetness and umami like tea polysaccharide and amino acid also lose activity after a long time heating.

Besides, steeping too long also makes the tea polyphenol oxidation, leading to an ugly infusion color. Like green tea will become dark yellow, sending out a cooked smell, miles apart from the original flavor. And to the high-fermented tea like Pu-erh, the infusion will become muddy after a long time steeping, lost the mellow and smooth taste.

You may question that when Tibetan makes butter tea, they keep cooking dark tea for a long time. How is the different from cooking tea in a vacuum flask?

First, due to the local high altitude, the water boiling point is lower than usual. Even under a long time of heating, the temperature can not reach 100℃.

Secondly, when cooking tea, the water stays in a boiling state, and the temperature is constancy. Even a high-performance vacuum flask can not keep the water at the same temperature all time.

Third, when most tea lovers in other regions cooking tea, they only cook for about 5-10 mins. And people who use a vacuum flask to make tea are planning to steep for a long time.

One more factor that affecting tea flavor is the material of the vacuum flask. We’ve talked in the post about teapots. Teawares in different materials will take a certain effect on the tea taste. Most vacuum flasks are made from food-grade 304 stainless steel, which will not let the tea got a metal smell. Still, stainless steel teawares are regarded as the lowest grade by tea lovers. And some vacuum flasks made from inferior steel or borosilicate glass may make the tea flavor becomes much worse.

Lost Benefits

Making tea lose its benefits is the biggest reason not recommend using a vacuum flask steeping tea.

Tea polyphenols are the main component that true tea brings benefits to the human body. They are composed of various flavonoids. The oxidation rate of these components will get faster once extracted, especially under a high temperature. And they will lose activity slowly and become some precipitates human hard to absorb.

A long time of steeping also increases the caffeine content in tea. Moderate caffeine can give a refresh and boost effect, but the overdose will stimulate nerves a lot, lead to insomnia and headache, etc., side effects.

Worthing to know, there was a rumor saying that due to tea tannin is easy to combine with metal ions, a vacuum flask with a metal inner wall will cause heavy metal poisoning if used to brew tea. Although it got some sense, the dosage still too few to get the poisoning standard, so it’s safe. Of course, for better getting the benefits from tea, don’t use the vacuum flask to steep tea often.

Hard To Clean

After enjoying tea, some tea stains may appear on the teawares if you don’t clean them thoroughly in time. The physical structure of a vacuum flask makes the clean job becomes more challenging. After a period of use, the inner wall may get tea stains, especially the place near the rim.

The tea stains are ugly(typically, you can not see them because they are inside) and affect the tea flavor. Even you only use the vacuum flask to store water, and the water also gets a strange taste. Besides, the tea stains are metallic compounds, and it’s easy to lead to some side effects to the human body if a long-term intake.

How To Use A Vacuum Flask To Steep Tea Well?

Even use a vacuum flask to steep tea is not an intelligent method; many of the time, it is the most suitable for a lazy guy. When you are going to make tea in this way, follow the points below, and reduce the effects on the tea flavor and benefits.

Only for storing hot water. You can do like Robert McCall in The Equalizer, package a teabag with a piece of tissue when going outside. You can make tea anytime and anywhere with the hot water in your vacuum flask. Some Japanese Sado performers also get used to doing it in this way.

Using a double-deck vacuum flask. Some vacuum flasks got an infuser and made the internal in a double-deck design. It can store the leaves and water separately. Although it can avoid making the tea at a high concentration by a long time steeping, the wet leaves are still getting oxidation inevitably.

Only store the tea infusion. After making tea, only fill the infusion into the vacuum flask to keep warm, without the leaves. It can let the leaves avoid a long time steeped and heating. But the infusion also will be oxidated slowly and lost flavor.

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