First, one point on nomenclature. When I refer to a Moka pot, stovetop espresso maker, or coffee percolator, I am referring to Bialetti's Moka pot, the most popular manifestation. While there are other products that use the same principle of steam to make coffee on a stove, most people have some version made by Bialetti.
How does a stovetop espresso maker work? It is composed of roughly three components: the base with a pressure valve which holds the water; the basket which holds the coffee; and the "collecting chamber" which the coffee brews into. Additionally, there is the metal filter and the "O" ring which ensures a good seal for the pressure to build and that the coffee grinds don't infiltrate your end product. The Moka pot creates stream by boiling water in the base that pushes water into the coffee hopper. Then, the water comes into contact with coffee, brewing, and then goes through the filter above the hopper, and into the collecting chamber. The whole process from heating the water to drinking the coffee is about 5-10 minutes.
I will focus on the "3 cup" Moka pot which I own as the basis for this guide. Remember, the designation of "3 cups" means three small espresso cups resulting in ~6-7 oz of liquid in total. It does not make 3 American-sized cups of coffee. If you want 3 large cups of coffee, the Moka pot is not for you, unless you buy the 12 cup Moka pot, which makes 25 oz of coffee.
Unfortunately, I must disabuse you of the notion that the Moka pot makes espresso. It does not. Let me repeat that. Stovetop espresso makers do not make espresso. They make strong coffee. Let me explain why. Espresso is brewed using around 9-10 bars of pressure. The Moka pot is capable of around 1.5 bars of pressure. This amounts to a difference in consistency, taste, and appearance, principally the lack of "real" crema you would see on good espresso. Additionally, the temperatures involved are different. Since Moka pots rely on steam to push water up, it requires the water to reach boiling, 212 Fahrenheit. Espresso machines, ideally, keep the water temperature around 202-5 Fahrenheit. What is the difference you may ask? Boiling water can burn the coffee damaging the delicate flavors of the coffee you just spent 20 dollars on. A rule of thumb for most coffee preparations generally advise to never allow boiling water touch coffee. Technically this is true for the Moka pot as the steam pushes non-boiling water into the coffee grounds (I think), but nevertheless a higher temperature is involved than in making traditional espresso. While espresso machines and Moka pots use pressure, the difference in pressure produced is significant.
If that wasn't complicated enough, there are two different versions of the Moka pot (besides the different sizes): aluminum and stainless steel. The aluminum version is the first Moka pot made by Bialetti and appears to be the most popular version, probably due to tradition, modern aesthetics, and the cheaper price. Unfortunately, there is one large issue with the aluminum version. Aluminum can impart a "metallicy," bitter taste to the coffee. To counter this, people "season" their pots by allowing a film of coffee oil cover the top chamber by not thoroughly washing it. I will address this later, but its an important issue to remember. The stainless steel Moka pot generally does not impart the aforementioned metallic taste. [Source for the two pictures is Bialetti's website]
In addition to the aluminum and stainless steel Moka pots, Bialetti makes one's that steams milk and brew coffee resulting in a cappuccino, and ones that are electric.
Brewing Steps and Tips:
First, let me walk you through how to brew with the Moka pot. At each step, I will introduce some helpful tips and hints to improve the end product. If you want a quick "how to," search James Hoffman's video on the Moka pot, and watch it.
0. Quickly wash out the base part with tap water and wet the the metal filter and O ring on the collecting chamber. I think it helps reduce the "metallicy" taste, especially if the Moka pot has been sitting for a few days with use.
1. Pour water into the base stopping where the pressure valve is. Any more and the water will prematurely contact the coffee grounds.
At this point, there are two "schools of thought." The first school of thought is to use cold water. The reasoning is more of habit than anything else. Reconsidering this reasoning, it really is not a "school," but that of uncritical thinking. The second school of thought is to boil the water in a teapot and pour this into the base. In doing so, this prevents the the stove from heating the whole Moka pot to an unpleasant temperature for the coffee which might cause it to burn. I'd recommend this method.
Be sure to use quality water! Water right out of the tap is drinkable, but it can also introduce unwanted tastes into your coffee. I suggest using a water filter to minimize the introduction of foreign elements into your perfect brew. Consider using a Brita filter or the like
2. Grind the coffee. Try to ensure an even distribution and flat surface. The hopper must be filled completely for the Moka pot to function properly. If it isn't, wonky things will happen..
This is sticking point for me. I have read and heard that the grind for Moka pot coffee should be just above an espresso setting on your grinder. They have forgotten that we are making strong coffee not espresso. From my experiences, a medium grind has produced the best results avoiding the bitter, over-extracted coffee that plagues the Moka. If you want to experiment with different grind settings, please do! I have found that the finer one goes, the more bitter the coffee tastes.
3. Screw on the top chamber with a dry towel (if using hot water). Make sure it is tight enough as the coffee can seep out where the base and the top chamber meet. Turn the stove to low-medium heat. On my gas stove, I ensure that the flame isn't touching the pot. Don't want it to burn or melt.
4. After a few minutes, the coffee will begin to come out of the spout in the upper chamber. After about half the chamber is filled, I cut the heat and remove the pot from the stove. I try to limit the watery end of the brew from diluting the quality coffee brewed in the beginning. However you do it, please do not leave the Moka pot unattended! This could lead melting, but more importantly the more the coffee is heated after brewing the bitter it gets.
5. Pour the coffee into your favorite coffee receptacle.
6. Before drinking, quickly run water over the collecting chamber to prevent coffee oils globbing all over the aluminum. By doing so, this ensures a nice uniform oily film to prevent a "metallicy" taste in future brews and doesn't allow the pot to get too dirty and gross. Proper "seasoning" of the pot should look something like this:
First and foremost, soap is generally a "no-no." Soap adds chemicals that can possibly alter the taste of your coffee in the future. If you must add soap, add the slightest, most imperceptible amount on a paper towel or rag, and thoroughly rinse the pot out after wiping it down.
After every use: Empty the spent grounds from the coffee basket, wash out the base, and run water over the collecting chamber. Dry everything with a rag, but do not wipe the inside the collecting chamber in order to keep those precious coffee oils. Let the three pieces dry separately. This will avoid having a dank, odorous smell later. After an hour, everything should be dried enough to assemble it back together.
After two-three weeks: Time to disassemble and wipe everything down, including the coffee oils that we have tried to so hard to cultivate. Sometimes they just need to go. They're probably getting a little stale. Additionally, the whole pot needs a good once over. This cleaning includes popping off the O-ring and the metal filter. Take a blunt, flat knife, slowly working it under the O-ring, while trying to carefully not to damage it. Use a lifting motion to pop it off. Remove the metal filter. It should come off right away as the O-ring was the only piece keeping it in place.
Now that everything is disassembled. Use a paper towel and wipe every inch of the pot. I advocate using a paper towel than a rag. A paper towel seems to absorb more coffee oils and "grime." Additionally, you can see how dirty the Moka pot really was! The only tricky part is getting the paper towel inside the spout of the Moka pot. I use a small pencil or thermometer and wrap the paper towel around it, then inserting it into the grimy, small space. Like so:
Two more cleaning ideas: One can use the Moka pot as normal but not add coffee. Thus as the water boils and the steam pushes the water upwards its helps remove some of the rancid coffee oils. The second idea, and I haven't done this, but instead of using water in the above methods, use vinegar. I would recommend a highly diluted concoction!