Infuser
A reusable perforated container for loose leaf: a basket that hangs in the cup, or a ball that sinks into it. Most of them are too small, and that is not an opinion. The interior volumes have been measured, and the popular spring-loaded ball holds enough leaf for about 213 ml of tea while the mug people drop it into holds around 350.
- Capacity
- 3 to 44 ml of dry leaf, depending entirely on which one
- Material
- stainless steel, glass, nylon or silicone
- Origin
- early twentieth century
- Best for
- loose leaf without a dedicated pot, if you buy a large basket
millilitres of dry leaf, at the one-quarter fill rule
- Oxo basket44
enough for 1577 ml of tea
- Nylon basket32
1143 ml
- Flower infuser10
371 ml
- Spring-loaded ball6
213 ml, against a mug of about 350
- Owl infuser6
208 ml
- Teabag5
189 ml
- Tea stick3
105 ml, under one teaspoon
Francl (2024), table 7.1. Interior volumes measured by glass-bead displacement, then divided by 4.5 because wet leaf expands more than fourfold. One millilitre of dry leaf makes about 35.5 ml of tea. The standard measure is 5 ml of leaf per 175 ml of water.
What it is
Two families. Baskets are open-topped and sit in the mouth of a cup or pot, so you can stir the leaf and lift the whole thing out. Balls are closed and fully submersible, usually on a chain. Materials run from stainless steel through glass and nylon to silicone novelties shaped like submarines and owls. Stainless steel takes the finest perforations; glass tends to have large holes that let fines through; silicone stays cool to the touch and, unlike the carbon-based plastics, sheds no microplastic particles.
What it does to your tea
It limits how much water can reach the leaf. Dry tea expands more than fourfold when wet, so leaf packed into a small container becomes a solid plug that water flows around rather than through, and the compounds that suffer most are the slow aromatic ones rather than the caffeine. Francl measured the interior volume of eight infusers by displacing glass beads, a method borrowed from meteorite measurement, and divided by 4.5 to get how much dry leaf each can hold with room to swell. The spread is nearly fifteenfold from a tea stick to a large basket. The disposable equivalent has been measured on the same axis and it corroborates all of this. A teabag is a membrane, so the rate-limiting step becomes diffusion across it and the caffeine rate constant comes out about 29 per cent lower than for the same leaf loose, while the eventual total is similar. What the bag costs is rate, not quantity, and nobody brews for the half hour it would take to make that up. The same mechanism explains why a pyramid bag brews faster than a flat one while shape at constant surface area changes nothing: a pyramid is not a shape change, it is more free volume, and leaf that can move extracts faster. That is what the UK Advertising Standards Authority accepted in 2014 when it declined to uphold a complaint against exactly that claim. Room, in other words, is the whole variable, in a bag and in a basket alike.
What it suits
Anything, if the basket is big enough. A large steel basket is a genuinely good way to brew, close to loose leaf in a pot. A small ball is suited to a small cup and to nothing else.
How to use one
Fill it no more than a quarter full, which follows directly from the fourfold expansion. Emma Elizabeth Piere was already warning against filling a tea ball more than two thirds in 1915, and even that is too much. Lift it out when the time is up.
How to choose one
Buy the biggest one that will fit the vessel, in stainless steel, with fine laser-cut perforations rather than a few punched holes. Whimsical shapes are the ones to avoid: they combine tiny volumes with a handful of holes, so the water cannot circulate through the leaf even if you underfill them.
Care and cleaning
Rinse immediately, because dried leaf in a fine mesh is far harder to shift than wet leaf. Steel and glass go in the dishwasher. Silicone is fine but holds smells from strongly flavoured teas.
What people get wrong
Matching the infuser to the vessel by eye. A tea ball looks like it belongs in a mug, and it holds a third of what a mug needs. If your loose-leaf tea comes out weak and you have responded by steeping it longer, the length of the steep is not the problem and lengthening it is why the cup is now also bitter.
What it is made of
Sources
- interior volumes of eight infusers, measured by glass-bead displacement, and dry-leaf capacity derived as interior volume divided by 4.5 Francl, M. (2024). Steeped: The Chemistry of Tea, table 7.1. Royal Society of Chemistry
- the first-order rate constant for caffeine extraction is about 29 per cent lower from a teabag than from loose leaf, while equilibrium concentrations are similar Spiro, M. & Jaganyi, D. Kinetics of tea infusion, parts 2 and 3. Food Chemistry
- the UK Advertising Standards Authority did not uphold a 2014 complaint against a pyramid teabag brewing-power claim, accepting test results showing greater infusion at 40 seconds and two minutes Advertising Standards Authority ruling, July 2014, on a complaint by Tata Global Beverages against Unilever