Vacuum flask
A double-walled vessel with the air evacuated between the walls, which nearly removes conduction as a route for heat to leave. For tea it is used two ways that should not be confused: carrying already-brewed tea, and carrying hot water to brew with later.
Identity
- Category
- Serving vessel
- Also called
- thermos flask, insulated flask, vacuum bottle
- Material
- Stainless steel or glass-lined steel with an evacuated cavity
- Typical capacity
- 350–2000 ml
- Skill level
- Beginner
Porosity
Not porous. It contributes nothing of its own to the liquor, so it can be moved between teas freely and washed with detergent without consequence.
Where it comes from
Modern and international, and central to everyday tea drinking in much of China, Central Asia and South Asia.
Named here rather than presented as generic equipment. The object belongs to a practice, and TeaHQ describes it from the outside.
If you do not own one
For water, any insulated container. For brewed tea, none is needed if the tea will be drunk within the hour — and brewed tea held hot for hours goes flat and stewed however good the flask is.
This one is not marked essential. The tea can be made without it.
Brewing methods it is used for
- Grandpa style — Leaf loose in a tall glass or flask, topped up with hot water through the day and drunk around the leaf. It is how an enormous proportion of tea is actually consumed in China, and it needs no equipment whatsoever.
- Samovar service — A strong concentrate held in a small pot, and near-boiling water held separately below it, combined in the glass at the moment of drinking. The drinker chooses the strength, not the brewer. It is the daily method across a wide band of Eastern Europe, the Caucasus, Iran and Central Asia, and the practices within that band are not one practice.
Care and maintenance
Tea leaves a film inside that ordinary rinsing does not remove; bicarbonate of soda and hot water clears it. Store it open and dry, because a sealed damp flask develops a smell that transfers to everything after.
Other serving vessels
Sources
This page is TeaHQ synthesis. No external source stands behind the description, the material or the account of how the object is cared for. Where the record names a tradition, that attribution is TeaHQ’s own reading of common practice rather than a citation.
TeaHQ names no maker, brand or shop and has nothing to sell. Nothing on this page should be read as advice to buy the object — the substitute note above exists because owning it is usually optional.
Written comparisons
Where TeaHQ has set this piece of teaware against something it is routinely confused with, and argued the differences out in full.
- Vacuum flask vs tea cosy — Two ways of keeping tea hot, and both do it well enough to cause the same problem. Whether that is a benefit or a fault depends entirely on one question: has the leaf been taken out?