- Created: Thursday, 18 December 2003 07:15
- Written by colin
Chapter Four - pump up the volume to better espresso.
In three chapters we have covered some of the basics; boilers, brew groups, portafilters, thermostats, pressure, and temperature. Our next topic is pumps and the mechanisms of moving the water through the ground coffee.
In the photo at right, I pulled out a boiler from Gaggia espresso machine.
Before I do that, let me touch very briefly on where the water comes from and where it is stored. The water, here in the Northwest, is remarkably soft and pleasant tasting. It is very low in added chlorine. Mineral content is low as well, probably as low as most commercial filtered water. The incentive to use bottled water, for me, is the ability to fill up the machine and not worry about the effects of the chlorine on the espresso machine components. To get around chlorine content in the water, let the water sit on the kitchen counter for ten minutes. The chlorine quickly leaves the water for the surrounding air.
Okay, I know you are impatient for the answer to this question. Where do you put the water? Do not laugh. I get this a lot. Truth is, the water is either in a reservoir or your machine is connected directly to a water supply. This direct connection is called 'being plumbed in'.
Chances are your machine has a reservoir and guess what, this kind of machine is called the pour-over. The plumbed in machine is generally of the semi-commercial category or restaurant variety. The advantage of the pour-over is that it can be anywhere in the home or office provided that there is running water and electricity nearby.
I digress. Let us talk about what moves our precious water around. In almost every case, your home espresso machine is going to be powered by a vibration pump. I do mean in almost every case. In fact, the pump in your machine is most likely an ULKA pump. They are everywhere. They are well designed. They are simple and almost indestructible. They have a line in, a line out and a connection for electricity. The pump is usually placed between the water supply and the boiler. The pump, in effect, pushes the water through the mechanism and, of course, provides the necessary pressure to brew the espresso coffee.
As we move up the food chain of coffee machines, the types of pumps start to vary a little. In many higher end machines the common pump is a volumetric one. I will not go into too many extra details on the properties of the volumetric pump. Suffice to say, it is a workhorse but, unlike the vibration pump, it is sensitive to being run dry. I will talk more about this later.
Finally, there is one system that I would like to identify. It is the hydraulic brewing system. Hydraulic brewing has a significant role in the history of espresso brewing but I will cover that in another article.
We find hydraulics in two distinct areas. One is the lever powered espresso machine and the other is the power assisted hydraulic espresso machine. The former is found in many homes under the name of Pavoni.
This unit is, quite literally, powered by muscle and the power of water pushed by the piston in the hydraulic mechanism. There are two types of lever units; Armstrong method and spring assist. I bet you can guess how the Armstrong unit works! The lever of the espresso machine is raised pulling water from the boiler into a cylinder.
Pushing the lever down drives the water through the brew group and portafilter. The beauty of this system is that it is whisper quiet. There is no pump. The only sound is the barista (you) straining to push the lever down as you meet resistance! In the spring assist machine, the action of raising the lever also engages a heavy steel spring. When the lever is pulled down to brew, the spring is released, assisting you in the brew cycle.
All things considered, once you are familiar with getting the grind right and the other oddities of these units, using the lever powered hydraulic espresso maker can be quite sexy.
In the industrial world of the working cafe, the powered hydraulic espresso machine can be just the thing for pumping out 400 cappuccinos per hour, but, hey, that is the beyond the scope of this discussion.
We now have the water. We have the machine. What do we have left? Electricity! Chapter Five!