27th
A Problem of Keeping Tea in a Thermos Flask
I thought tea in a Thermos flask should be the easiest thing in the world to make, but as it turns out, the operation is fraught with difficulties. Or, perhaps more accurately, fraught with only one difficulty: but a gravely serious one.
I speak only of Stinky Tea.
This has now happened to me on a couple of occasions. I would be setting off on a long train journey from Edinburgh to my parents’ house near Portsmouth. First thing in the morning, I would brew tea in the teapot, put milk in the flask, and pour the tea on top. Screw the lid on tight, and away we go. But no: halfway through the journey, in need of refreshment, I break out the Thermos, and something is not right. The tea is rancid. I have a flask full of undrinkable Stinky Tea.
On the first occasion, I thought that perhaps there had been something nasty growing in the flask before I put the tea in, or otherwise that the milk had been bad and I’d not noticed. But on a little reflection, it seems this is not the case.
Tannins act as a defense mechanism in plants against pathogens, herbivores and hostile environmental conditions. Generally, tannins induce a negative response when consumed. These effects can be instantaneous like astrigency or a bitter or unpleasant taste or can have a delayed response related to antinutritional/toxic effects.
My theory is that the tannins in the brewed tea are adversely reacting with proteins in the milk, causing it to go rancid. I guess that when milk tea is made and drunk immediately, there is insufficient time for this reaction to occur. However when the milk tea is made and kept hot in the Thermos for a few hours, Stinky Tea is the inevitable and unfortunate result.
