Chapter Three- Let's illustrate the bits and pieces that make up a machine. In the last couple of chapters we have tried to make it clear that water temperature and brewing time are two critical areas where espresso coffee is concerned. Water has to be 195 degrees, give or take a few degrees. When it comes to keeping the water temperature stable it often helps to look at the physics: Whichever components are not heating the water, or insulating the water from the outside world are taking heat from the water. This is a very important concept to remember so read it over a few times.
Okay, so let's start at the head end of the process by going through the bits and pieces one at a time and explain their importance. The chassis or frame of the espresso machine: is it plastic or metal and does it matter? Well, think about heat retention or transmission. Is it going to protect the internal components from temperature variation and still look good? Do you want or need to heat cups on the top of the machine? You might be asking yourself: Why would I want that?
Good question. Think about it. If you want to heat the environment around the machine then you are wasting energy and adding a level of destabilization to the whole process of maintaining a constant temperature.
Truth be told, many machines do have metal shells and a place on top to place cups. It is not that these units get that hot because there isnít really that much power involved. Additionally, it is not the desire of the engineer to heat your kitchen with an espresso machine. Moral of the story: If you see a plastic thermal shell unit, like the Gaggia Baby, and you like the look, buy it.
Let us talk about what heats the water. Generally, a boiler heats the water. What is a boiler, you ask? A boiler is a vessel that has a cold water line going in and a hot water supply coming out. In the world of espresso machines, the boiler is heated by an electrical element that is either embedded in or wrapped around the boiler.
A boiler can be made of many materials. Some common materials are steel, aluminum and brass. What we are looking for in a boiler is the ability to heat up fast and retain the heat once the boiler and its contents (water) have come up to temperature.
Now, when you think about this for a moment, the ability of a full boiler to come up to temperature quickly implies that it is a good conductor of heat. The ability of the boiler to retain the heat effectively indicates the properties of an insulator. Do you know what the conundrum is? That is right, folks! You cannot have it both ways. In a perfect world you cannot be an insulator and a conductor.
The desire is to have a system that retains heat. This desire generally takes precedence over the ability for the machine to heat quickly.
Now it would be nice if everyone used a marine brass boiler in every machine because that would be the best choice. It is slow to heat up. It resists corrosion. It is slow to cool off. There is a downside. Aluminum and steel is cheaper and in the marketplace, the savings on the production line make for a cheaper machine for the consumer. Aluminum is quick to heat up. It is corrosion resistant and it is cheap. Stainless steel is a good choice too.
Okay, you ask. What is the boiler doing? The boiler is providing water, at 195 degrees, to brew coffee and steam for heating milk. How can this be? How can you provide steam from a boiler full of water that is cooler than boiled water? Well, in most machines there is a ingenious arrangement of switches and thermostats to provide the functions of power, brewing and steaming. There is a minimum of two thermostats required to do the job right. What is a thermostat? A thermostat is an electrical device that opens or closes a switch contact when a specific temperature is achieved. In the average espresso machine there is a thermostat that cuts the power to the boiler when the temperature of 195 degrees is achieved and a thermostat that cuts the power when a temperature of 220 degrees is achieved. How do we get steam from an espresso machine?
There are a variety of neat methods and I will not cover them all. Besides, this is a guide for dummies, right? The guide for rocket scientists has not been written yet.
The quickest way of drawing steam off of a boiler is tapping the boiler with a pipe and feeding this line through to the steam wand. In an up and down world it would make sense to draw steam off of the boiler from the top of the boiler but this is not really necessary. When water exceeds the boiling point, in the boiler, it is ready and willing to take the path of least resistance to the outside world. So, with this in mind, we can tap into the boiler anywhere that is convenient.
Ultimately, we want to brew coffee with the water that we have gone to all the trouble of heating and stabilizing. We need to move the water from the boiler to a place where the coffee is. We do not want the water to lose too much heat on the way to the coffee so it makes sense to have it as close to the boiler as possible. The brew group is what we call the components that bring the coffee in contact with the water.
The brew group should be made of the same material as the boiler but it is not always the case. The best material for the brew group is brass. The brew groupís job is to move the hot water to the ground coffee and the shorter the trip for the hot water, the better. Think of the brew group as a sealed bath shower. Think of the shower arrangement in your bathroom that could wash your hair without getting the rest of you wet. Good analogy? No? Well, okay.
Something has to hold the ground espresso coffee during the brew cycle. This something also has to double as a filter. The first misconception that many people have about all espresso machines is: Where is the paper filter? There is no paper filter. It is actually a basket that attaches to something we call the portafilter.
This basket can be made out of stainless steel. It can come in a variety of sizes and shapes that serve a couple of purposes. Obviously, as water passes through the espresso coffee, we need to keep the fluid (the espresso coffee) and the spent coffee grounds separate. This is what the filter basket is for. Again, the filter basket can come in several sizes depending on how much espresso coffee we wish to brew.
We have identified the portafilter. Perhaps you have seen one in a cafe. It looks like an ice-cream scoop. It has an insulated handle and a scoop that holds the filter basket. Perhaps you have guessed that the portafilter is made out of brass or some heavy-duty heat retaining material. You are correct. On to Chapter Four.