1

I'm new to making espresso.

I bought a Gaggia Classic machine for home use.

It sometimes pours slowly, sometimes more quickly -- slower if I tamp the coffee well i.e. press hard.

My theory is:

  • Gaggia Classic machines are factory-shipped with too much pressure, i.e. 14 bar, so they can also handle coffee pods
  • The recommended pressure for espresso machines is more like 9 to 12 bar.
  • With the pressure too high, the water might force a channel through the coffee, instead of seeping evenly
  • By tamping the coffee hard and thoroughly, I avoid that so it does seep slowly

My question is -- is this "hack", i.e. tamping the coffee hard, good enough? Or should I for some reason make the effort to lower the machine's pressure?

2
  • If I search the manufacture's website, I find this page for "New Classic", which says the pump is set to 15 bar. Perhaps you can link to another page if this is not your model?
    – hardmath
    Apr 7, 2023 at 18:01
  • I bought it new, recently. The user manual calls it "the new Classic" and doesn't mention the pressure or taking it apart.
    – ChrisW
    Apr 7, 2023 at 20:33

2 Answers 2

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It's not directly the pump that is the problem, but the OPV, the over pressure valve, which diverts the water back to the tank when a certain pressure is exceeded.

For this reason, if you want to change your machine to 9 bar, look for OPV mod instructions online.

as r mac noted, the pressure is actually controlled by the coffee puck, the problem with a machine which produces up to 14 bar is that you cannot visually determine when you have adjusted grind, dose, and tamp to the recommended 9 bar. Even if the puck is too dense, the water will be pushed through just fine; but the resulting coffee will be sub-optimal. After adjusting the OPV, you can see when you reach the point where the flow will be just right, and anything denser will choke.

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Short answer: no. Tamping harder will not have the effect you desire.

The machine's pump by itself does not produce pressure. Pressure is created when the flow of water is interrupted by the coffee grounds. This will cause flow to stop while the pump works to push water through the grounds.

Tamping harder will in the worst case lead to a buildup of greater pressure, not lesser. In the best case, because coffee grounds are often rigid (depending on grind) and can't be "smushed", it may make no difference at all.

A more reliable solution would be to grind slightly coarser. Go slow with increases and test each stop. A coarser grind will reduce the amount of compaction tamping causes, which will reduce pressure buildup.

Note that ideal grind size varies with bean variety and grinder. You may need to adjust grind size if you start purchasing a new brand of coffee, or you may ideally want to adjust for every new package of coffee you open, as even same variety batches may have minor differences between them.

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  • Thanks, I think your answer is saying that the pump does not affect pressure, that only the grind and the tamping affect pressure. Well in that case, for any given grind and tamping, what is the effect of having a machine set to 14 bar instead of 10 -- what is the effect of the so-called increase?
    – ChrisW
    Apr 5, 2023 at 6:17
  • Is it untrue that if the machine has a lower maximum pressure, then the flow rate will be slower for any given grind and tamping?
    – ChrisW
    Apr 5, 2023 at 7:36
  • The pump does affect pressure, but not variably. That is, the pump "pushes" water. The strength of the push is what decides how much force (in addition to other involved apparent force like "gravitational effect") the water ends up applying to the coffee once the water can't flow anymore. If you run two tests controlling for grind coarseness and tamping but with different pumps, the different pumps will produce different pressures. But all three of those factors end up influencing actual pressure: pump "strength", grind size, and puck compactness.
    – R Mac
    Apr 5, 2023 at 13:11

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