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.