Most Espresso Machines in North America are Configured for Production Speed Rather Than for Espresso Quality
Espresso machines are expensive pieces of hardware, costing from about $3,000 to as high as $15,000 for a two-group machine. Quite often it represents an important portion of ones investment in an espresso bar. In any case, it is a critical part of ones operation and if the machine goes down, you are essentially "out of business."
Despite their high costs, these machines perform only three basic functions: First, they heat up the water to between 195 deg F and 205 deg F for making espresso. If that is all that was required, one could accomplish it using a stove and a kettle.
Second, they pre-measure the amount of water delivered to the porta filter when a particular button is pressed; the exact amount of water depending on how that button is programmed. If that was all that was required, one could use a stove, a kettle and a measuring glass.
Unfortunately, most machines are programmed to deliver too much water, some as much as 4 oz when making a double shot of "espresso." This is based on the mistaken belief that more is always better. We will address this problem in a future newsletter.
Third, they deliver the water to the porta filter under pressure; pressures as high as 10 bars or 140 lbs per square inch. Without this high pressures, one simply cannot make real espresso. The stove top devices that claim to make "espresso" at home seldom develop pressures above 2 bars and are incapable of producing espresso of any kind. At best they produce strong coffee.
Using Water Pressure in the Wrong Way
Most practitioners of the art of espresso outside of Italy, employ the pressure generated by these machines in the wrong way. Instead of using it to drive the oils out of the ground coffee, they use it to speed up the passage of water through the coffee so as to make the "espresso" in 14 seconds, or less. If it takes less than 20 seconds from the time the button is pressed till the end of the pour, one simply cannot produce real espresso, only ordinary coffee.
The machine people have only helped to exacerbate the problem by speeding up the delivery of water so as to make the "espresso" in shorter and shorter times. Most of the machines are reconfigured for production speed rather than espresso quality before they are shipped to North America or installed here.
When hot water comes into contact with the ground coffee in the porta filter, some portion of the ground coffee simply dissolves in the hot water. Actually, one fifth of the ground coffee, by weight, is soluble in water and ends up in the cup. Ideally, only about two ounces of liquid should have been produced in making a double shot of espresso and will be about five times as strong as ordinary brewed coffee.
Real purpose of the water pressure is to drive out the oils that are present in the ground coffee. These oils just do not mix with water. Instead, they form tiny droplets and swim in the coffee concentrate. This dispersion of oils in the coffee concentrate constitute an emulsion; and it is this emulsification of oils that actually converts strong coffee into real espresso.
Emulsifying the Coffee Oils
When oils in ground coffee are emulsified, all measurable properties of the liquid are changed. Density, viscosity, surface tension, flow rate, wetting power, foam forming ability, of espresso are all different from those of ordinary coffee. Real espresso is in fact a very different liquid, not coffee any more.
So are all the flavor properties. For example, when one takes the first sip of real espresso, the oils in the emulsion coat one's taste buds and thereafter one's ability to detect bitterness is markedly reduced. Thus, the second sip will be less bitter and the brain will use this information to interpret the second sip to be sweeter. Hence, if one make real espresso and ordinary coffee using exactly the same blend, the espresso will be a whole lot sweeter.
The process of pressurizing water results in packing energy into the water molecules. In the process of making real espresso, this entire energy must be used to break the bond between the oil molecules and the ground coffee particles and drive these oils out. Once that is accomplished, there should be little or no energy left in the water for it to gush out of the porta filter. The resulting brew should simply ooze out of the porta filter like molten chocolate (see photo).
If one does not succeed in driving the oils out, there would be too much energy left in the water as to make the liquid coffee gush out of the porta filter with the characteristic noise one hears at most espresso bars in North America.
Assuming you are using a blend that is specifically designed to produce quality espresso, the secret then is to grind the coffee fine enough and tamp it hard enough so as to impede the flow of water through the coffee puck. Instead of gushing out, the pressure should be used to force the water to penetrate the interior of the ground coffee particles and dissipate all its energy in driving out the oils, in addition to extracting the solubles.