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I recently switched from a Bialetti Moka Express 3-cup stovetop espresso maker to a Cloer 5928 espresso maker. It has an integrated heating unit, just like an electric kettle, so making a coffee is now much more energy-efficient.

The coffee from the Bialetti was flawless (using a medium-fine grind of Starbucks espresso roast beans). Now I have a difficult time producing coffee that is not both overly thin (underextracted) and has an odd taste that I can't even describe (perhaps from overheating the ground coffee?).

The new espresso maker takes some time to heat up (365 Watts of electric power), and then the coffee is pressed through relatively quickly in short bursts.

Having a look at the funnel, it has a hole, unlike the funnel of the Bialetti. My questions are:

  1. Can the hole in the funnel have anything to do with the underextracted coffee?
  2. What could be the purpose of the hole anyway?

enter image description here

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+50

Just guessing here, but the hole could keep the water from going up until it reaches a certain temperature. The amount of pressure from the steam varies on the temperature of the water, and if there weren't enough pressure, the water would recycle. However, if the pressure were greater, the velocity of the water would prevent it from dripping out of the hole.

This could explain the bursts, since the pressure would rise and fall depending on the amount of water it pushed out. The more water that escapes, the more room there is left behind for pressure to fill.

Also, you mentioned a weird taste. Could it be metallic? If so, you could try letting the base sit in a strong coffee/water mixture for a couple days. The moka pot needs to be seasoned to prevent this taste, so I would recommend not washing it with soap - just rinse. My grandmother has never washed hers.

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    Only season it that way if it's stainless steel. Aluminum will rot and corrode in very few days (personal experience). – luser droog Nov 18 '15 at 1:09
  • All surfaces in the Moka pot are indeed from stainless steel. I guess that I should give it a try. – DCTLib Nov 18 '15 at 9:03
  • Hi user3814472, I've awared you the bounty, but I refrained from marking this answer as accepted as you wrote that you are guessing what the hole is good for. Thanks for your answer! – DCTLib Nov 19 '15 at 10:03
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My guess is that this particular machine might be defective. No such hole can be appreciated on the amazon page or in the manual, and should that be actually a hole, physics may make it hard for such a machine to brew coffee properly (edited) .

Therefore

Can the hole in the funnel have anything to do with the underextracted coffee?

Absolutely yes Most likely

What could be the purpose of the hole anyway?

Either it is a defect, or is (part of) a valve meant to stop the water from circulating until a pressure threshold is reached.

A bit more in detail:

A Bialetti/Moka pot brews when the vapor pushes hot boiling water through the ground coffee, and stops brewing when the water level decreases down to the funnel tip and vapor finds his way out making that sound.

A hole in the funnel is like a hole in a drinking straw. Liquid won't be pushed upwards once the hole is not submerged anymore.

I guess any coffee you are brewing is from vapor that has condensed in the upper vessel instead of escaping.

Some pots are designed to only brew above some pressure. For example they might have a pressure valve which is like a hole with a spring that keeps a cap pressed until the pressure is reached.

In this case we see a spring, but it looks it is just intended to facilitate the funnel extraction.

Also such valve would operate in the opposite direction: At the pressure threshold it would close instead of opening.

P.D. The OP noted he found images through google where such hole could be found. I found http://www.ebay.de/itm/DEFEKT-Cloer-5928-Espresso-Kocher-/331539918656 but it is a bit unclear if such item is defective as well (disclaimer at description). Also hole seems to be a bit higher and a bit more narrow. Another funnel with hole

  • Javier, thanks for your answer! I also looked at the manual, and the photo/figure of the funnel may have simple been taken from the side without the hole. But you are right: I should investigate an error in production. The spring is just there to make the funnel pop out a bit when you unscrew the upper part of the body - then, it is easier to grab. – DCTLib Feb 6 '17 at 8:58
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    Hmm, a quite google image for "Cloer 5928" search finds a few images in which the funnel has a hole as well. – DCTLib Feb 6 '17 at 9:04
  • DCTLib You are right, there is such image at a sold item at ebay.de/itm/DEFEKT-Cloer-5928-Espresso-Kocher-/331539918656 I am editing my response – Javier Feb 10 '17 at 15:00
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the intention of the hole at the funnel is to avoid water coming up to early and to increase the mocca temperature. Some water will come back through the hole and give the water more time to boiling. The hole has nothing to do with the safety valve which you can see below the thread at the lower body. From the taste there is not big difference having the hole or not. With the hole the mocca is even a little stronger, boiling time is a little longer. Question: Did you use the same coffee amount at the Cloer and Bialetti and weight it? Can you increase the coffee amount (but do not press it)?

Best regards

V. Andres from Cloer Quality Control

  • Welcome V. Andres for the nice answer. Could you please ask your ongoing question as a comment to the original question? So, @DCTLib can answer it at one place. – MTSan Feb 24 '17 at 5:30
  • Sorry, due to iam new i cannot comment on the original question. – cloer-anvi Feb 24 '17 at 8:47

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