Espresso pot

Espresso pot in the design of the Moka Express (on a camping gas flame )

The espresso pot , in Italian caffettiera or more often moka , is a device for preparing coffee on a stove .

The octagonal model is the Moka Express , which was developed by Alfonso Bialetti and only manufactured after 1945, when other providers from Italy followed suit. Except for the external shape, these jugs are largely identical to the models from the pre-war period, such as those made in France, Austria and Hungary. They are produced in different sizes, indicated in the number of mocha cups (60 ml) that can be prepared with one filling. Today there are espresso pots made of more durable stainless steel ("stainless steel"), which also enables other designs. Unlike aluminum models, jugs with ferromagnetic inserts in the bottom can also be used on induction cookers .

The discussion about the "wrong" name

The term espresso pot, which is only widespread in German-speaking countries, is misleading because it cannot be used to make espresso : The pot generates a maximum pressure of around 2.5 bar, whereas a brewing pressure of around 9.0 bar is required to prepare an espresso, such as it is produced by espresso machines .

Apart from the different taste, even a layperson can quickly tell the difference between a correctly prepared espresso and a coffee prepared with the "espresso pot" / moka pot: among other things, due to the lower pressure, no stable crema is formed in the espresso pot .

In Italy itself, besides bialetti or moka , the device is usually simply called caffettiera , which simply means coffee pot and is also used for other coffee making devices. The product made with it is also simply referred to as caffè , just like the "real" espresso. Since it is customary in Italy to prepare coffee at home with the moka pot, but to go to a bar for an espresso, the respective meaning of caffè arises from the context: At home this means the coffee prepared with the pot, outside the home, this is the Caffè Espresso .

A “more correct” designation (as used by the Italians) would therefore be Moka- jug (their original name). This in turn causes further confusion of names, because it is often misunderstood as “Mocha” - which describes a different type of coffee worldwide, namely Mocha prepared in Arabic, Turkish or Greek .

In Austria, where devices for preparing coffee have been made of aluminum since the beginning of the 20th century, the jug is called a mocha machine, which initially seems more consistent because there the espresso is sometimes also referred to as mocha .

Layout and function

Espresso pot and its individual parts

construction

Working method

An espresso pot consists of three parts. The lower part of the jug (1 / A) or the kettle is filled with water. The coffee powder is poured into the funnel insert (2 / B) and the top part of the pot (4 / C) with riser pipe (3) catches the finished coffee. When heated on the hob, the water in the kettle begins to evaporate. This creates an overpressure that pushes the hot water in the kettle through the coffee powder in the funnel insert. The coffee then flows through a fine sieve on the underside of the top part of the pot, rises in the riser pipe and runs from above into the top part of the pot.

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X-ray video of an espresso pot in operation

If the espresso pot is blocked, the water vapor escapes through a safety valve (5) on the kettle. After preparation, there is always some residual water in the kettle, which prevents immediate overheating. However, the coffee starts to boil in the top part of the jug if the jug is left on the heat source for too long.

use

First the espresso pot is unscrewed and the funnel insert removed.
The boiler is now filled with water. The amount of water can be varied as desired; however, the safety valve must not be covered by water.
The funnel insert is reinserted and filled with coffee powder. The powder is not compressed with a pounder as is usual with portafilter espresso machines.

Half the amount of coffee can be prepared with the help of a reduction sieve, which is now included in many espresso pots.

The top of the can is screwed back on firmly.
Now the espresso pot is placed on the hob and heated. Aluminum pots do not get hot on induction hobs because aluminum is not ferromagnetic .
When the water starts to boil, the upper part of the pot fills with coffee. At the end a clear hissing sound can be heard, as there is now steam in the riser pipe.

The pressure

The pressure with which the water is pressed through the coffee grounds depends on the density and granularity of the coffee grounds (this has an additional filter function). The safety valve (5) in the lower part of the jug (1) limits the maximum pressure to 1.5–3 bar. With extremely fine and highly compressed grist, a pressure can build up in the lower kettle that is so high that the valve responds and the steam in allows the ambient air to escape. If, on the other hand, water escapes through the screw cap of the two halves of the can, the can was not screwed tight enough or the sealing ring is defective.

The heat supply

The higher the temperature and correspondingly higher the steam pressure, the faster the water is pressed through the coffee, as the higher the power input, the steeper the temperature curve (isochoric heat input). An increased power supply has less of an influence on the water temperature with which the coffee is extracted, since the resulting increase in pressure changes the boiling point only slightly. The speed of water penetration through the coffee powder determines the extraction time and therefore has a decisive influence on the dissolution of the aroma and tannins. The coffee granularity must therefore be adapted to the desired water flow rate and vice versa (see filter coffee ): If the water flows too quickly through the funnel insert, the coffee powder may have been too coarse or the funnel insert insufficiently filled and the coffee develops too little aroma. Coffee powder that is ground too finely or powder that is too strongly compressed in the funnel insert, on the other hand, leads to bitter or burnt-tasting coffee.

To the crema

With the classic espresso pot, no or only a slightly volatile crema can be created.

However, there are further developments that have a pressure valve at the upper end of the riser pipe. This pressure valve is also called cremator or crema valve and holds back the water in the boiler until a certain pressure is reached. Only at this pressure is the coffee pressed through the cremator, which gives the espresso a more consistent crema.

Arguments against the aluminum can

There is disagreement among toxicologists and trophologists as to the extent to which the classic aluminum cans leave residues in the drink, which would be unhealthy and have a negative impact on the taste. Bad treatment of the aluminum surface can actually lead to such residues, because scratches, salt and lye attack the aluminum, whereupon residues can even be detected on the tea towel. It is questionable to what extent such possible residues significantly increase the daily aluminum intake through food, medication, etc. The strongly alkaline solution in the dishwasher causes (unpainted) aluminum to turn black, and aluminum parts in the dishwasher lead to poor washing results for all other items to be washed with the same load. According to a study by the Federal Institute for Risk Assessment , water or, better still, coffee should be boiled and thrown away in aluminum cans before drinking for the first time. After this process, the measured values of dissolved aluminum are well below the limit value of 5 mg / kg, which is why aluminum cans can be described as harmless if handled correctly. Washing in the dishwasher should also be avoided, as increased aluminum values were detected afterwards (although still below the limit value). Traditionally, the jug and its parts are rinsed with water without additives. This way it does not come into contact with alkalis and develops its typical patina . Nowadays also available espresso pots made of stainless steel are not affected by the problem of dissolved aluminum.

Any cookware with an aluminum base is unsuitable for induction hobs. Alternatively, jugs made of stainless steel or with a double bottom are available, which are marked as suitable for induction . There are also isolated electric jugs that have an integrated heating element, similar to a kettle .

Arguments for the aluminum can

The main argument for an espresso pot made of aluminum is the heat distribution. With λ ~ 2.4 W / (cm K) and κ ~ 1 cm² / s, aluminum is one of the best heat and temperature conductors. Stainless steel has only about one twentieth of these conductivity values. In addition, the aluminum can is thick-walled (due to its strength), whereas the walls of stainless steel cans are thin. When heating up, an aluminum jug is therefore heated quickly and evenly. This also applies to the top of the can. The steam pressure drives the boiling water through the coffee powder into the top of the jug, which has already been heated to around the boiling point. The coffee is hot.

An aluminum jug usually does not contain nickel. In contrast, nickel is the essential component in stainless steel. This could be a consideration for allergy sufferers when choosing the type of espresso pot; because nickel is the cause of the most common contact allergies. Two in ten people are allergic to the metal.

Curiosities and trivia

A forerunner is a coffee maker developed in 1819 by a French tin smith named Morize , which was very popular under the name Caffettiera Napoletana until the second half of the 20th century, especially in southern Italy .
Renato Bialetti , Alfonso Bialetti's son, who aggressively marketed his invention after the Second World War and thus gained worldwide fame, was buried in an oversized espresso pot used as an urn.