Medium-fine — finer than filter coffee, but coarser than espresso. About the texture of fine sand. Too fine makes the coffee bitter and can block the water flow. Never tamp or press down the coffee grounds.

What grind size do I need for a moka pot?

Medium-fine — finer than filter coffee, but coarser than espresso. About the texture of fine sand. Too fine makes the coffee bitter and can block the water flow. Never tamp or press down the coffee grounds.

Why this is the case

A moka pot (often called a Bialetti) works using steam pressure — roughly 1.5 to 2 bars, which is significantly less than a real espresso machine (9 bars). As the water in the lower chamber boils, the steam pressure forces the hot water up through the coffee grounds. The contact time is shorter than pour-over filter coffee, but longer than espresso.

This middle ground between pressure brewing and gravity brewing requires a grind size that also sits perfectly in the middle. If the coffee grounds are too fine (espresso grind size), the lower pressure of the moka pot might not be able to push the water through at all, or it will flow so slowly that the coffee heavily over-extracts and becomes incredibly bitter. In the worst-case scenario, dangerous pressure can build up in the lower chamber. Conversely, if the grind is too coarse (filter grind size), the water shoots through too fast, leaving you with thin, watery coffee.

The target zone is fine sand. It should be finer than table salt or sea salt, but not as powdery as espresso. When you rub the grounds between your fingers, you should feel distinct individual grains, but it shouldn’t feel coarse or gritty.

A very common mistake: tamping (pressing down) the coffee grounds in the moka pot basket. While tamping is required for an espresso machine, it is dangerous for a moka pot. The low steam pressure simply cannot penetrate a compacted puck. The result: blocked flow, excessive pressure buildup, and in extreme cases, the safety valve will trigger. You should only loosely fill the basket and level it off with your finger — never press it down.

If you are buying pre-ground supermarket coffee for a moka pot, look for blends specifically labeled “for moka” or “stovetop espresso”. Universal grinds (meant for drip machines) are usually a bit too coarse, and true espresso grinds are too fine.

In practice at Green Wall Coffee

At Sophienstraße 27, when we grind beans for a moka pot, we set our grinder one full step coarser than our espresso setting. For guests making coffee with a Bialetti at home, I recommend: a medium-fine grind, always start with hot water (not cold) in the lower chamber, place it on medium heat, and take it off the stove the second it starts to gurgle. With the correct grind size, moka pot coffee tastes strong and punchy, but never bitter.

Related questions

• How to brew coffee in a moka pot?
• What grind size do I need for espresso?
• Why does my moka pot coffee taste bitter?

For more depth on the subject, check out our article on how to make perfect espresso. Or visit us at Sophienstraße 27 — Mon–Fri 8am–5pm, Sat 10am–5pm.