A Tea Addict's Journal

Adventures with a thermos

January 29, 2015 · 14 Comments

So I’m currently in Shanghai doing some research, which means being in a library all day. This being China, you can bring a thermos into the library, and each reading room has a table for you to put your thermos along with everyone else’s. I figured that since I can’t drink tea otherwise, and I don’t want to wait till I get home before brewing some, I would try bringing tea in a thermos.

I had in mind not just the regular giant plastic water bottles that people use here (mostly seen in cabs) where they stick an obscene amount of tea in there and brew all day. I thought I would try something a little different, using a thermos with very good heat retention and see how the tea brews in there. It seems like an interesting thing to do – high heat, continuous brewing. Turns out it’s not such a great idea. The tea is very strong, obviously, because it is brewed for hours in very hot water. It brews super strong, but because of it, it’s hard to discern flavours. I think the effect was similar to what you might see in a samovar – long brewed strong tea that probably could use some dilution.

What’s most interesting is that when I poured out the contents and then diluted it with some water, the taste is, well, inferior. It just doesn’t taste quite right, since it’s a tea I know well. It’s also interesting that the wet leaves are very, very mushy – when I poured water in the cup it stirred up a lot of bits of tea leaves. Again, the effect is similar to boiling the tea for a long period of time. You extract everything out of it, and it loses all ability to be re-brewed.

So, long story short, if you are going to grandpa your tea on the go, use a vessel that loses heat normally over time, instead of something that retains heat exceptionally well. It doesn’t really work.

Categories: Teas
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14 responses so far ↓

  • ira // January 29, 2015 at 10:42 am | Reply

    i brew my tea with a gaiwan like you normally would several times and store the tea in the stainless steel thermos. I then would add hot water often if I can throughout the day, never wait till tea soup is completely gone. It will last a good portion of the day.

  • Jakub // January 29, 2015 at 11:15 am | Reply

    Agreed. I found a surprising difference even between a thick-clay glazed gaiwan (which loses heat very slowly) and a thin porcelain one, especially lighter teas were far better from the thin porcelain (I suspect this might be also why I think porcelain better for lighter teas than clay pots)… I guess it just has something to do with teas emitting tastes at certain temperature and given rate – and if the exposure to a temperature is too long, it can go wrong.

  • Adrian // January 29, 2015 at 2:10 pm | Reply

    Some teas are better than others about this, though. I’ve had pretty good luck with Taiwanese wulong that’s of at least a baseline quality, as long as I don’t use too much leaf. Some is better than others, but at least it usually stays palatable. Some cheap aged wulong or a small amount of a decent shu can also work well.

  • Will // January 29, 2015 at 2:54 pm | Reply

    I’ve had the same problem, and have found that brewing with the lid off til the water cools a bit helps a little bit, but brewing ahead of time and then putting into the thermos also works.

    I have a Zoji thermos that retains heat *really* well, so the tea will just stew in there, even if it’s not at a full boil when it goes in.

  • Su // January 29, 2015 at 7:56 pm | Reply

    Try it with less leaves if you’re using fresh. I usually thermos grandpa with the spent leaves of a particularly good brew so as not to waste it.

  • Jennifer Wren // January 29, 2015 at 11:17 pm | Reply

    I have found that just putting several leaves (usually an oolong) in a thermos with hot water and taking it with me on a hike yields a decent cup, still hot, later in the day. Not as nice as everyday brewing, but two hours into a hike on a winter’s day it’s excellent.

  • Von Monstro // January 30, 2015 at 12:24 am | Reply

    This reminds me about how I used to brew tea initially, and how I still enjoy doing it sometimes with teas that come out ok with the method. I used to get a teapot around 700ml, throw in maybe two teaspoons or so per “cup” (6oz/~180ml), use appropriately heated water (often as hot as possible for most teas I drank), and just leave it in there for a few minutes, and then begin drinking at a regular pace, never manipulating the infusion further other than pouring more cups of tea. This can either make a tea that is what you’d expect; something very tannic, sour, etc.; but sometimes it makes for something very invigorating and different from what the expected. In an experiment in which I wanted to return to this style of brewing, one roasted oolong, that usually came across more fruity to my senses, was very bitter in later infusions this way, but also pleasantly more roasty and earthy. I felt immediate stimulation from the brew as well. I used to like my tea something like Russian Chifir’, but not quite so extreme.

    Perhaps water not quite as hot could work okay this way with some teas.

  • David // January 30, 2015 at 3:33 am | Reply

    I often carry a thermos of tea while ski touring. I use a 16oz zojirushi one and the tea stays hot for hours, which is great when you’re at the top of a mountain and it’s freezing cold and windy and you need something to warm you up. I’m usually rushing in the morning and pre-brewing 16oz takes a whie, so instead I just put leaves in a bag and pour in hot water.

    The problem, of course, is what leaves to use. I’ve had a couple bad experiences where wuyi oolong or hongcha came out basically undrinkable. The safest bet is shu puer. Decent sheng can work too if you use much less leaf than usual. I’ve also used jasmine pearls (again with less leaf than usual). Perhaps the most satisfying overall was a strong shu with milk and a little sugar. Not something I’d usually admit to drinking, but in those circumstances, getting some easily-digested calories along with your hydration is a useful bonus.

  • su // January 30, 2015 at 9:33 am | Reply

    Older teas do better in a thermos too I find. The green stuff n new shengs get bitter pretty quickly. So mainly , less leaves , older tea or if using younger tea , then oolongs/yancha with at least medium roast. But of course u’ll never get a brew that tastes as good as a good gong fu brew in a thermos. The thermos is for when it’s not convenient to have a proper brew. It is however , I feel , not impossible to get a reasonably drinkable brew in a thermos. U just have to experiment a bit.

  • Wulf Nesthead // February 14, 2015 at 12:00 pm | Reply

    Some wonderful ideas here, this is such a grand and informative place!
    If excessive heat-retention is a concern, perhaps a tea which is customarily boiled can be used if one is going grandpa-style with a thermos?
    Some types of hei cha come to mind.

  • Michael Eversberg II // March 12, 2015 at 11:30 am | Reply


    Leo Kwan over at Tea Guardian did a thing on tea in the thermos a couple years back:

    His folks used a thermos as a teapot when he was a kid. These days, he brews tea up fairly weakly and carries it sans leaf. This is also the method I use. He has also established a bit of a “pecking order” in terms of tea he feels does particularly well vs those that do not.



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