MOKA EXPRESS
The Moka Express is a stovetop
espresso maker, based on the principle of preparing coffee with pressurized
boiling water.
It was created by Alfonso Bialetti in 1933. It is originally made from aluminum
with bakelite handles.
In Italy, where Bialetti (the manufacturer)
is based, the Moka Express (or cheaper imitations) is in almost every home.
Elsewhere, it is known as an iconic design, displayed in modern industrial art
museums, such as the Science Museum in London.
Mokas come in different sizes, from one to eighteen coffee cups.
The Moka does not produce true espresso, but rather a double-strength coffee.
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Fig.1 cross section |
First water is poured in the boiler (marked A on Fig.1), then the funnel-shaped metal filter (B) is inserted. Finely ground coffee is added to the filter.Do not compact the coffee. The upper part (which has a second metal filter at the bottom) is tightly screwed on the base. By placing the pot on a heat source, the water is brought close to boiling point creating steam in the boiler. A gasket ensures a tightly closed unit and allows for pressure to safely build up in the lower section, where a safety valve provides a necessary release in case this pressure would get too high (with clean filters, that should not happen).
The steam eventually reaches a high enough pressure to gradually force the surrounding boiling water up the funnel through the coffee powder and into the upper chamber (C), where the coffee is collected. When the lower chamber is almost empty, steam bubbles mix with the upstreaming water, producing a characteristic gurgling noise.
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Moka Pot being loaded |
As with percolators, the pot should not be left on the stove so long that the coffee boils. Ideally, with a little practice, it should be removed from the heat before it actually starts gurgling--usually, when only about 1/2 of the top chamber has been filled.
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A Moka Pot produces a rich dark brew
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Due to the higher pressures involved, the mixture of water and steam reaches temperatures well above 100 °C, causing a more efficient extraction of caffeine and flavors from the grounds, and resulting in a much stronger brew when compared to that obtained by drip brewing. However, since a typical moka cup is about 30 ml, the actual amount of caffeine per serving is smaller.
Moka pots are generally inexpensive and easy to maintain. The pot only requires periodic replacement of the rubber seal and the filters.
After use, a coat of greasy coffee residues is left lining the interior of the stems, filters and upper chamber. This thin layer protects the coffee from contact with the aluminum wall, which might otherwise give a slight metallic taste to the coffee. To avoid removing the lining, it is advisable to use only water or mild soap to wash the moka pot. When this precaution is followed, the more the pot is used, the better the coffee tastes.
When a well used moka machine is left idle for some time, the coffee grease inside may turn rancid. If this occurs, it is advisable to fill it with slightly soapy water and put it on the heat as if to make coffee. The water will remove any unpleasant-tasting residue. Also if the rubber seal is replaced, the new rubber can give the coffee a bad taste on the first couple of uses. To avoid this, a new rubber seal should be primed by using the moka pot once or twice with water only, or with used coffee grounds.
One should also periodically examine the safety valve to ensure that the mechanism is free of blockages and will function in the case of an unnatural pressure build up.
The original Moka Express was made of aluminum. However, intake of aluminum oxide is thought to be connected with Alzheimer. Therefore, modern Moka Express pots are made of steel.
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