How Does a Moka Pot Work?
Understanding how a moka pot works can help you improve the taste of your coffee and solve issues related to burnt flavors or watery coffee.
Moka pots are intelligently designed to generate enough pressure to brew coffee similar to espresso, using simple components. The moka pot consists of six main parts:
The upper chamber: Collects the final coffee and has a handle and a spout for pouring.
The filter plate: Prevents ground coffee from entering the final brew.
The gasket: Seals the gap between the filter plate and the upper chamber.
The funnel/basket: Holds the ground coffee.
The lower chamber: Contains water and has a safety valve.
The safety valve: Prevents the moka pot from exploding.
Assembly:
The lower chamber is filled with water. The funnel, filled with ground coffee, is placed in the lower chamber so its base is submerged in the water. The upper chamber, which contains the gasket and filter plate, is screwed onto the lower chamber.
Once the moka pot is assembled and placed on the stove, the brewing process begins.
How Does the Moka Pot Work?
As the water in the lower chamber heats up, some of it turns into steam, filling the air inside the chamber.
As the water temperature rises, the steam occupies more space, and pressure begins to increase.
Since the steam has no outlet, it pressurizes the water, which is forced upward through the funnel at the bottom, passing through the ground coffee and rising into the spout in the center of the upper chamber.
As the water passes through the coffee grounds, it absorbs the flavor, aroma, and color, creating the final brew.
It’s important to note that the water does not need to reach a boiling point for the moka pot to work. The steam generated by very hot (but not boiling) water can create enough pressure to push the water through the coffee grounds.
Why Is High Pressure Generated?
High pressure is essential for several reasons:
First, finely ground coffee requires higher pressure to prevent water from being blocked as it passes through.
Imagine pouring water over very finely ground coffee — the water would simply sit on top. Pressure is needed to push the water through the coffee grounds.
Second, higher pressure water is more efficient at extracting carbon dioxide from the coffee grounds, which is necessary to form foam.
What Affects Pressure?
The pressure needed to push the water through the funnel and coffee depends on several factors, but it comes down to four main variables:
Gravity: The force pulling the water downward. This doesn’t change unless you're brewing coffee off-planet!
Air pressure: The force exerted by the weight of air molecules in the atmosphere, which the water must overcome.
Filtration pressure: The force needed for water to pass through the coffee grounds, primarily depending on grind size.
Water temperature: The hotter the water, the more pressure is generated by steam.
The amount of pressure needed to operate the moka pot is less than you might think — a study showed it averages only 3.2 kPa, which is about 1/30th of standard atmospheric pressure.
What Is the Role of the Safety Valve?
The safety valve is a mechanism that releases steam when a certain pressure level is reached to avoid the risk of explosion.
If the coffee is ground too fine or tamped down too hard, it can create a barrier that increases the required pressure, sometimes to a dangerous level. In these cases, the safety valve will release steam.
It’s very important not to fill the water in the lower chamber above the level of the safety valve, as this would prevent it from functioning!
Understanding How the Moka Pot Works Helps You Improve Your Coffee:
Understanding the forces at work in a moka pot can help you improve your coffee brewing technique.
Using a fine grind: Regardless of the brewing method you use — whether it’s a French press, espresso machine, or moka pot — fine grounds produce stronger and more intense coffee. Finely ground coffee offers more surface area for the flavors to dissolve in water.
In the moka pot, the effect of using a fine grind is even more noticeable. Finely ground coffee makes it harder for water to pass through, increasing water pressure, and producing more carbon dioxide in your coffee, creating more foam and a richer drink.
Remember — if the coffee is ground too finely, it may block the water entirely, causing the coffee to burn in the funnel and upper chamber. The result would be bad-tasting coffee or no brew at all.
Using a coarse grind: A grind that’s too coarse is less problematic, but you may find that the lower pressure produces an under-extracted, watery brew.
Tamping the coffee: Tamping the ground coffee — pressing it down in the filter as you would when making an espresso shot — increases water pressure and results in a stronger coffee. However, this is not recommended, as it increases the chance of blockage and over-extraction
Comments