Paper, metal, cloth

The filter decides the texture

Dissolved coffee gets through any filter. What differs is everything else: oils, and fines, the particles too small to see singly. Both add weight and blur the flavors a little, like mist on a view.

Body against clarity

Hold the oils and fines back and the cup turns lighter and clearer. That trade — body against clarity — is the whole choice. Tap a filter and watch the two bars swap places.

Paper: the clear one

Tap the layers. A paper filter catches nearly all the fines and most oils, so the cup is clean and bright, almost tea-like; Chemex paper is thicker still.

• Dissolved coffee: Goes straight through every filter. This is the coffee.
• Oils: Paper catches most of them, and the cup turns clean and bright.
• Fines: Nearly all held back, so nothing blurs the flavors.
• The bed: The grounds stay put, whatever the filter is made of.

Rinse the paper

Most recipes rinse the paper first, to warm the brewer and wash out any papery taste. With good white paper the difference is small; brown paper usually earns it. Brands drain at different speeds, so a new box can move your brew time.

Metal: the heavy one

A metal filter — the French press mesh, a steel cone — lets the oils through, and some of the finest grit. Rounder and heavier, with a little silt at the bottom; leave the last sip. It needs a proper wash.

Why the mesh needs washing

Everything a filter lets through, it has touched.

Why does a metal mesh need a proper wash?

Answer: The oils it lets through cling to it and go rancid. The oils it passes cling to the mesh and turn rancid. Paper is thrown away before that can happen.

Steel, the South Indian way

Filter kaapi, South India’s everyday coffee, drips between two stacked steel cups. Water seeps through fine coffee, often cut with chicory, for 10–15 minutes into a thick decoction made for hot milk.

Why so strong?

The golden ratio, 1:15–1:17, is for a drip or press cup you drink black. The decoction breaks it on purpose.

Why is the decoction brewed so much stronger than 1:15?

Answer: It is mixed with hot milk before drinking. Hot milk finishes it: about 1 part decoction to 2–4 parts milk, with sugar. A decoction brewed at 1:15 would come out thin once cut like that.

Cloth: the fussy one

A cloth filter sits between the two: most fines held, some oils through. The catch is care, as with orchids — rinse it, keep it in water in the fridge, skip the soap, and replace it once it stops smelling clean.

Which filter makes which cup

Which filter makes which cup?

• Paper — Clean, bright, tea-like
• Metal — Round and heavy, a little silt
• Cloth — Weight and clarity at once

Paper is the clear one, metal the heavy one, cloth the one that gives you both — and asks for care in return.

A footnote for your heart

Paper also holds back most of the cafestol, a coffee oil that can raise LDL cholesterol in people who drink a lot of unfiltered coffee. Paper is the easy switch; your doctor, not an app, is the one to ask.

Workplace machine coffee, boiled coffee, French press — what do they share?

Answer: Little filtering, so more cafestol gets through. Little or no filtering. Boiled, press and even some workplace machines carry cafestol that paper would have caught.