Tea cosy
A padded cover that goes over a teapot. It looks like the most sentimental object in tea and it is one of the few with a measured effect: a quilted cosy halves the rate at which a porcelain pot cools, and a felt-lined steel one cuts it by a factor of three.
- Capacity
- sized to the pot
- Material
- quilted fabric, felt, or felt-lined steel
- Origin
- Britain, nineteenth century
- Best for
- a leaf-free pot you will drink over half an hour
What it is
Quilted fabric, felt, or a rigid felt-lined steel shell that sits over the pot like a lid for the whole thing. Some ceramic pots have the same idea built in, with a felt-lined lid.
What it does to your tea
It traps air, and air is a poor conductor. Tea loses heat mainly by conduction into the pot and then into the room, plus convection off the surface, and a cosy slows both: the trapped air conducts badly and the cover stops the steam carrying heat away. Measured, the felt-lined steel version kept tea above drinking temperature half an hour after brewing. The trade-off is that it works just as well on the leaf: a cosy on a pot with the leaf still in it does not keep the tea warm, it keeps the tea extracting.
What it suits
A pot of Western-style black tea you will drink over half an hour, where the leaf has already been removed. It is wasted on gongfu, where the pot is emptied within seconds.
How to use one
Take the infuser out first. Then cover the pot completely, including the spout if the cosy has a flap for it, since an uncovered spout is an open chimney.
How to choose one
Felt-lined and rigid beats quilted and soft, by a measured factor of about one and a half. Beyond that, it needs to actually fit your pot: a cosy with a large gap at the base loses most of the benefit.
Care and cleaning
Wash fabric ones occasionally; they pick up tea splashes. Keep them dry, since a damp cosy left over a warm pot is a good way to grow mould.
What people get wrong
Leaving the leaf in under it. That is the most common use and it is the one that ruins the tea: you have built an insulated over-extraction chamber. Decant into a second pot or remove the basket, then cover.
What it is made of
Sources
- a quilted cosy slows a porcelain pot's cooling by a factor of two and a felt-lined steel cosy by a factor of three Francl, M. (2024). Steeped: The Chemistry of Tea, chapter 7. Royal Society of Chemistry