Moka pot

The moka pot is a coffee maker designed for use on a stove or electric burner. It works by using vapor pressure and the expansion of heated gas to push hot water through a bed of ground coffee. Its name comes from the Yemeni city of Mokha, and it was brought to widespread attention by Alfonso Bialetti, an Italian aluminum seller, along with his son Renato, beginning in 1933. The device quickly became a standard part of Italian life. Bialetti Industries still makes the original version, sold as the "Moka Express."

From Italy, the moka pot spread and is now most common in Europe, Latin America, and Australia. Its design is considered iconic and is displayed in museums of modern industrial art and design, including the Wolfsonian-FIU, the Cooper–Hewitt, National Design Museum, the Design Museum, the London Science Museum, the Smithsonian, and the Museum of Modern Art. Moka pots are available in various sizes, producing anywhere from one to eighteen servings, each 50 ml (2 imp fl oz; 2 US fl oz).

The original design, along with many current models, is made from aluminum with Bakelite handles, though stainless steel or other alloys are also used. Some versions have an upper half made of heat-resistant glass.

**Use**

Moka pots are placed on a heat source, typically a flame or electric range. Stainless steel pots, but not aluminum ones, can be used on induction cooktops.

A typical moka pot has three main parts: - The lower chamber, or boiler, which includes a safety valve to prevent too much pressure from building up. - The filter funnel, or basket, which presses against an annular rubber gasket when the pot is assembled and creates a seal with an upper filter disc. - The upper chamber, or collector, where the finished coffee collects during brewing.

To assemble the moka pot, the filter funnel is placed into the lower chamber. Then the upper chamber is screwed onto the lower one, compressing the rubber gasket against the rim of the filter funnel to seal the lower chamber. The upper filter disc is usually held in place on the bottom of the upper chamber by the rubber gasket, which acts like a flexible internal circlip; this disc keeps coffee grounds from moving up into the spout.

**Preparation**

The boiler (marked A in diagrams) is filled with water up to an etched line, or just below the safety release valve. Home users generally do not preheat the water, though doing so can speed up brewing in commercial settings. The metal filter funnel (B) is then inserted, and finely ground coffee is added. How tightly the coffee is packed affects how quickly it extracts and the strength of the final brew. The collector (C) is attached, and the pot is placed on heat.

**Brewing**

Heating the boiler (A) causes a gradual pressure increase from both the expansion of trapped air and the rising vapor pressure of the heated water. Once the pressure is high enough, it forces the water up through the funnel and through the coffee grounds. The brewed coffee then rises up the vertical spout and pours into the upper chamber (C).

When the lower chamber is nearly empty, bubbles of steam mix with the rising water, creating a characteristic gurgling sound—a sign that brewing should stop. Researchers Navarini et al. call this the "strombolian" phase, where a mix of very hot steam and water passes through the coffee, leading to rapid overextraction and unwanted flavors. Unlike a standard percolator, the moka pot never sends brewed coffee back through the grounds.

Several physics papers published between 2001 and 2009 used the ideal gas law, Darcy's law, and the temperature-dependent vapor pressure of water to explain the moka pot's brewing process.

**Moka coffee characteristics**

The flavor of moka pot coffee depends heavily on the bean variety, roast level, grind fineness, water composition, and the heat level used. Moka pots are sometimes called stove-top espresso makers. However, typical moka coffee is extracted at low pressures of 1 to 2 bar (100 to 200 kPa), while espresso standards require 9 bar (900 kPa). So, moka coffee is not considered espresso. The moka pot typically uses a coffee-to-water ratio by mass of about 1:10, resulting in a brew with roughly 3–4% dissolved solids. For comparison, espresso is "stronger" with 9–10% dissolved solids, and drip-brewed coffee is "weaker" with about 2% dissolved solids. The caffeine content of moka coffee has been measured at 128–539.9 mg per 100 mL.

**Maintenance**

Moka pots need periodic replacement of the rubber seal, cleaning of the removable filter, and a check to ensure the safety release valve is not blocked. All parts should be scrubbed by hand with water, avoiding detergent, as aluminum moka pots are not dishwasher safe.

**Aluminium migration**

The possibility of toxic amounts of aluminum migrating from an aluminum pot when brewing an acidic beverage has been scientifically studied. It was found to be "negligible"—below 1% of the recommended total weekly intake level after a new pot has been used. After the pot stabilizes at below 1% with regular use, migration rose to a maximum observed level of just under 4% after a dishwasher cleaning, which is why dishwasher use is strongly discouraged.

**History and variants**

The principle of using steam to force heated water through a bed of roasted, ground coffee dates back to at least 1818, according to a patent by Elard Römershausen for a very large machine. A more portable machine using the same basic idea was designed by Louis Bernard Rabaut in 1822, based on drawings submitted to the French Academy of Sciences, followed by similar designs by Andre Caseneuve (1824), Edouard Doublet, and Pi.