The Best Grind Size for a Phin

What medium-coarse looks like

Rub a little between your fingers. It should feel gritty and distinct, like coarse sand or the raw sugar you get in a café packet. You should be able to see individual particles without looking hard.

If it feels like flour or smooth powder, that is espresso grind and it will choke the phin. If it looks like coarse breadcrumbs, that is French press grind and the water will fall straight through.

Why a phin needs this particular range

A phin has no pressure. Water sits on top of a bed of coffee roughly two centimetres deep and works down through it under its own weight. Two things have to be true at once.

The bed must seal. The press plate does not compress the coffee; the coffee swells during the bloom and pushes up against the plate. A grind that is too coarse leaves too much space between particles for that seal to form, and water finds a channel round the edge.

Water must still pass. A grind that is too fine packs into something close to a solid, and the drip stops entirely.

Medium-coarse is the band where both hold. It is narrower than it is for most brew methods, which is why grind is such an effective lever here.

Reading the drip

The drip tells you the grind is wrong before you taste anything.

What you see	What it means	What to do
Done in under 2 min	Too coarse	One step finer
A steady drip, done in 4–6 min	Correct	Nothing
Barely dripping at 8 min	Too fine	One step coarser
Nothing at all	Much too fine, or press too tight	Loosen the press first, then grind coarser
Fast, and water visible round the edge	Channelling	Level the bed and reseat the press — this may not be grind at all

That last row matters. Channelling looks like a too-coarse grind, but grinding finer will not fix it. Check that the bed is flat and the press is sitting square first.

Grinder settings, roughly

Settings vary between grinders, so treat these as a starting point rather than a specification.

• Hand grinders (1Zpresso, Comandante, Timemore): roughly 26–32 clicks from zero on most models — a touch coarser than you would use for a V60.
• Baratza Encore: around 20–24.
• Blade grinder: possible but difficult. Pulse in short bursts, shake between them, and accept that you will get fines and boulders together. A slower drip than expected is normal.

Buying pre-ground, and when not to

Almost all Vietnamese coffee sold domestically is pre-ground, in the right grind, and it works. For most people starting out, this is the sensible option.

The cost is aromatics. Ground coffee has enormously more surface area than whole beans and loses most of its volatile aromatic compounds within two to three weeks of grinding — faster in a bag that has been opened repeatedly.

Dark-roast robusta is somewhat more forgiving here than a light arabica, because much of what you are tasting comes from roast development rather than from delicate origin character. That is a real mitigation, not a reason to ignore it.

If you drink Vietnamese coffee more than a few times a week, a hand burr grinder is the single change that will improve it most. See grinders.

One thing not to do

Do not grind finer to compensate for not having enough coffee in the chamber. If the bed is too shallow, a finer grind will slow the drip, but it does so by compacting rather than by sealing — and compacted beds channel. Add coffee instead.