Stove-top coffee makers are an attractive alternative to a space-eating grime-collecting espresso machine. Interestingly, there are many general instructions of how to use it available, but few really concise descriptions of what to do and avoid when using stove-top espresso cookers.
The classic model, the Moka Express, is made of aluminium. This article claims that the coffee fat creates a protective layer inside the pot that prevents the coffee from tasting metallic. Not mentioned is that undefinable blobs of whitish goo tend to form in the lower compartment of an aluminium cooker, even if the device is kept dry and clean when not in use. Under pressure, the aluminium clearly reacts with either the coffee or the water or both. After a while, the inside of the Moka Express thus gets increasingly rougher – aluminium is being washed away. I would never wait for a metallic taste to manifest itself: there can be no doubt that some aluminium gets transferred from the pot’s inside into my own inside all the time. I don’t like thinking about what it would do there, so I am using stainless steel espresso cookers. With a little care and understanding, one can create a very decent cup of espresso with one of these.
– One has to know how one’s choice of coffee will behave in the confinement of the metal filter. This knowledge will have to be based on experiments with different grinds and with different degrees of compacting the coffee in the filter. Usually, a medium-coarse grind and very little or no compacting will do fine (too much compacting always gives poor results because it would require more pressure in the lower compartment than necessary to activate the safety valve, so the steam leaks out of the valve instead of pressing the water through the coffee). Some very fatty coffees tend to clog the filter and require a coarser grind.
– The water level should be somewhat lower than usually recommended. For most of the time, I am using a pot that accommodates 1/4 l when filled up to the hole of the safety valve. I usually fill it with no more than 200cl of water, so the water level stays somewhat below the entire safety valve. When using the whole amount of water, the last boiling-hot three tablespoons or so of water that run through the worked-out coffee extract highly undesirable aromas. To appreciate the full impact of the horrible rubber and cellulose aromas of this last portion, one can give the coffee of the first half to the guests and drink the last sip separately. Once will be enough to verify my point.
There are two advantages with a lower water level. On the one hand the water is gone before the coffee gets worked out as described above. On the other hand, the steam chamber is greater to begin with and the steam will develop sufficient pressure even before the water actually boils (Steam compresses. Bigger chamber = more compressed steam = more effect, or shall we call it leverage…). Not-actually-boiling is a good thing here (ah, I should mention that, of course, even not-quite-boiling water produces steam). I suspect (I can’t really look inside and ask, can I?) that – with a lower water level – the driving-out process of the coffee is completed before the water in the lower chamber gets substantially too hot for the good of the aroma.
One drawback of this type of coffee maker is that it certainly gets at least a little too hot at one point (the other drawback is the overall relatively low pressure). Typically, an espresso cooker carefully loaded with high-quality coffee and not too much water first produces an abundance of crema-like foam
(no real crema, I fear, but I am not a crema snob), which will run successively clearer. In this case the aroma test will show that the last part of the coffee is a bit weaker than the beginning, that’s all.
– The rubber seal must be tight. In new 4-cups-cookers (or bigger), or cookers with a new seal, this is a real problem. The rubber needs to get worked in. At the beginning, several batches of coffee will not process properly, because steam will leak out at the sides. Why ‘4-cups cookers’? Because the friction of the rather wide seal prevents proper tightening of the top part. Then again, I might be able to tighten a coffee pot when angry, but not to open it again after use. After a while, the seal should cease to be a problem, at least if one takes care to keep the rubber really clean. I regularly scratch out any embedded coffee grains with the handle of a spoon.
– The cooking temperature must be low. On gas stoves, this is very difficult to achieve, and so I would use a metal plate to dissipate the direct heat of the flame. On my ceramic stove, I heat the espresso cooker up on high for a minute at most; then I readjust the heat to the lowest possible effect. The coffee will now slowly and steadily run through.
– cheap non-espresso kinds of coffee cannot be used. I once almost lost two good friends by giving them, in an unfortunate moment of low brain activity, Moka Express-processed roasted-sawdust-type coffee-at-work. I mean, they almost ran away.