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Should the grind size for moka pots be as fine as that for pump espresso machines? I've seen some say mokas need fine grind size; others say fine/medium.

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  • Coarser than espresso (but finer than for pour-over / filter coffee) because otherwise this happens.
    – Stephie
    Jan 14 at 9:17
  • @Stephie What exactly is "this"? Accumulation of grinds in the water pot?
    – Geremia
    Jan 14 at 23:21
  • Amongst others, yes. And if the powder is too compressed by chance (because of course one shouldn’t tamp anyway) or cloggs the metal filter, you get a sort of “explosion”. Not pretty.
    – Stephie
    Jan 15 at 15:02

1 Answer 1

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Should the grind size for moka pots be as fine as that for pump espresso machines?

No, pump espresso machines generally require a finer grind than moka pots.

The reason for this is that moka pots operate at low pressure, 2 bar at the most. Pump espresso machines, on the other hand, brew at a much higher pressure of 8 to 10 bar.

So why does this affect grind size? In moka pots you don't want to grind too fine because the device is built for low pressure. If you grind too fine and tamp it really well then the water might not pass through as well at that low pressure. That can cause the brew to take a lot longer or it might trigger the emergency pressure valve.

With espresso machines (assuming you're using a regular filter basket, not a pressurized one) you need that finer grind so that pressure can build up. If the grind is too coarse then the water will flow through easily at lower pressure and you don't get an espresso as prescribed by some.

Of course it's possible to brew coffee using an espresso machine at lower pressure. Instead of making an espresso, that can be used to get a lungo using the same brew time.


As posted on home-barista.com, Britta Folmer's The Craft and Science of Coffee p. 313 lists an average grind size of 0.250mm for espresso and 0.300mm for stove pots (e.g. moka pots):

Typical average particle sizes and fines content for different brewing methods from Britta Folmer's The Craft and Science of Coffee

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  • What size should the grains be, exactly? I've seen 1/36" (0.8mm) recommended for espresso machines. My moka's funnel has probably that size holes, and the upper filter has even smaller holes, so I'm assuming the grind size should be no smaller than these holes.
    – Geremia
    Jan 14 at 23:20
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    @Geremia The Craft and Science of Coffee cited on home-barista.com recommends median particulate size is 0.25mm for espresso. With super automatics listed at 0.35mm, I think that'd be a good starting point for moka pots also. They list 0.6mm for filter coffee, so that's really too coarse for espresso and probably on the coarse end for moka pots too.
    – JJJ
    Jan 14 at 23:27

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