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CoffeeHQ

Filtration

Cloth coffee filter

Also known as: coffee sock, sock filter, flannel filter, nel filter, bolsita, coador de pano, manga de café, colador, café de media, tung dtom kaffee, silk stocking filter, pantyhose filter

A reusable filter of woven cotton or flannel, used across an unusually wide range of traditions — the Malaysian and Singaporean kopi sock, the Costa Rican bolsita, the Brazilian coador de pano, the Japanese nel drip flannel and the cloth strainer used for café Touba. Cloth sits between paper and metal: it holds back most grounds like paper but passes far more of the coffee's oils, which is why cloth-filtered coffee is usually described as fuller-bodied and rounder than the same coffee through paper. How to keep it between uses depends on the cloth, so follow its maker: one maker of a felt-filter cold brew system says to keep its filter damp, sealed and in the freezer.

Type
Filter
What it is for
Filtration

In short

A cloth filter is a piece of woven cotton or flannel, shaped as a sock on a wire hoop, a cone for a dripper or a disc for a siphon. It is the oldest kind of coffee filter still in daily use and the standard one in a long list of coffee traditions.

It makes a distinctive cup and costs almost nothing. What it asks in return is care between brews, and most disappointment with cloth comes from not being told that.

What cloth lets through

Tendency, not a guarantee

Paper absorbs coffee oils and traps nearly all fine particles, giving a clear, light cup. Metal mesh lets oils and fines pass, giving a heavy and slightly cloudy one. Cloth holds back the particles much as paper does while letting more of the oils through. The usual description of the result is a full, rounded texture without the silt.

The weave matters. Flannel with a raised nap on one side filters finely and drains slowly; a thin plain cotton drains faster and passes a little more. And a cloth changes with use: as oils build up in the fibres it slows down, which is one of the signs that it needs deep cleaning or replacing.

Preparing a new cloth

Widely documented

  1. Wash the new cloth in plain hot water, without detergent or fabric conditioner, to remove sizing and loose fibres.
  2. Simmer it in clean water for a few minutes. Some people add a spoonful of used coffee grounds to take away the taste of new fabric.
  3. Rinse it, wring it gently and fit it to its hoop or holder while damp.
  4. Before every brew, rinse the cloth with hot water. This warms it and wets the fibres so the coffee drains evenly.

Storing it: fully wet or fully dry

Widely documented

Kept wet, in the fridge
Rinse the cloth thoroughly straight after brewing and keep it submerged in a covered container of clean water in the fridge, changing the water daily. This is the usual practice with flannel drip filters used every day.
Dried completely
Rinse thoroughly, wring out and hang it somewhere airy until it is completely dry. This is common with cotton sock filters and suits occasional use; before the next brew, soak and rinse it in hot water. It is not right for every cloth: the seller's page for one well-known flannel drip pot says it is paramount that the cloth is never allowed to dry out, and has it washed and kept in a bag in the fridge. Where the filter's maker gives an instruction, follow that.

Why the in-between state ruins a cloth

CoffeeHQ explanation

A cloth left damp at room temperature is a warm, wet fabric full of coffee residue. It sours, and it can grow mould. The oils held in the fibres also turn rancid on exposure to air. Either fault goes straight into the next brew, and it is why cloth has a reputation in some quarters for tasting stale.

Wash a cloth with hot water only. Detergent and soap lodge in the weave and flavour the coffee for many brews afterwards. If a cloth needs more than rinsing, simmering it in fresh water is the standard remedy.

Signs a cloth is finished

CoffeeHQ explanation

Brews take much longer to drain than they used to

Usually because: Oil and fine particles have clogged the weave.

Change first: Simmer it in clean water; if it is still slow, replace it.

A sour, musty or rancid smell

Usually because: The cloth was stored damp, or the oils in it have gone off.

Change first: Replace it. A cloth that smells bad will not be rescued by rinsing.

Grounds getting into the cup

Usually because: The weave has thinned or a seam has opened.

Change first: Replace the cloth; the hoop or frame can be kept.

Who cloth suits, and who it does not

CoffeeHQ explanation

Cloth suits someone who brews daily and will make the rinse-and-store routine a habit, and anyone who wants the body of a metal filter without the sediment. It also produces no paper waste.

It is a poor choice for occasional brewing, shared kitchens and travel, where the cloth is likely to be left damp. Paper is the low-effort alternative with a cleaner cup; a metal filter is the low-effort alternative with a heavier one. How long a cloth lasts depends on the fabric and on how often it is used, so replace it on the signs above and not on a calendar.

What to do next

Where it fits

How much each kind of filter holds back

CoffeeHQ explanatory model — not a measurement

From most held back (first) to least held back (last).

  1. Thick paperHolds back the most oil and nearly all fine particles. The clearest, lightest cup.Chemex-style brewers
  2. Standard paperAbsorbs most oils and traps fines. Clean, with a little more texture.Cone and flat-bottomed drippers, filter machines, AeroPress
  3. ClothStops particles much as paper does and lets more oil through. Rounded, without silt.Nel drip, sock filters, siphons
  4. Metal meshPasses oils and the finest particles. Heavy, slightly cloudy, with sediment.French press, reusable cone and disc filters, phin
  5. No filterEverything stays in the liquid and the grounds settle in the cup or pot.Turkish coffee, cowboy coffee, cupping

Basis: Reasoned from what each material physically allows through. Limits: A tendency for the same coffee and recipe. Paper thickness, weave and mesh size vary by maker, and the rungs overlap in practice.

Preparation traditions

Named regional traditions that use this vessel or filter, from CoffeeHQ's international preparation atlas.