Chapter 5 of David Schomer's "ESPRESSO COFFEE"

(Ⅴ)

Chapter V Commercial espresso machines

From whom do you buy the machine?

In my business workshops, there are always a lot of people asking, "which espresso machine is the best?" I often say perfunctorily, "A machine that can move is best." It sounds rotten at first, but after you have heard my sincere and in-depth analysis, you will know that "moving" is a prerequisite.

If you want to open a shop and do business, before you spend money on a machine, ask: does the local agent have technical support? Do you have spare parts in stock? If you are unlucky and the machine dies at 07:00 on Sunday morning, who will call for help? Can only ask the Devil SWAT team for help? That's too bad!

If you want to fix some small problems yourself, ask first:

Is the agent willing to support you?

Are you willing to provide parts?

Are you willing to provide telephone consultation service?

If the agent is not willing to tell you how to adjust the maintenance or is not willing to provide parts, change it!

Requirements for espresso machines

No matter how many cups you boil, you should be able to provide constant temperature hot water continuously.

When cooking, the pump pressure should be stable.

The espresso machine should have the function of "pre-immersion".

Can supply constant pressure and dryness of steam, man-machine interface should be easy to operate.

Constant temperature hot water

No matter how many cups you boil, you should be able to provide constant temperature hot water continuously. Let's talk separately.

The biggest challenge for espresso engineers is the temperature control of the outlet head. (I will discuss it in more detail in Chapter 7). At present, there are two design methods to deal with this problem:

* single boiler type: use heat exchangers.

* double boiler type: one for steam generation and one for boiling water.

One of the fundamental problems is that after locking the hand, it is heated by the outlet head. Unfortunately, because the handle and filter basket are exposed, the surrounding air flow disturbance will continue to dissipate heat and interfere with the heat balance. To make matters worse, there will be some changes in the temperature of the machine at the outlet. The two reasons are merged into one, so the range of water temperature in contact with coffee powder is actually very large.

The severity of the problem depends on whether your machine is busy or not. When the machine of the heat exchanger is idle, it will slowly heat the water head. When the machine of the exclusive water boiler is idle, the outlet head will be reduced by several degrees.

In a good espresso machine, the outlet head should be wrapped to keep warm. The outlet heads of some machines are glittering and dazzling. In fact, this is not a good thing, because the heat dissipation of this brilliant surface is too serious, resulting in a greater change in the temperature of the outlet head.

In the 1950s, Italian engineers developed espresso machines in the form of heat exchangers. The original idea is that when hot water is used, a small amount of hot water is quickly heated from cold water in order to get fresh water for cooking. The steam boiler used is basically used to heat the water used to make coffee. Part of the reason for the development of this machine is that Italian water quality is mostly high in minerals, which can cause fouling in boilers. And the water filtration equipment at that time is not perfect, but now there is an excellent water filtration system, coupled with the nickel lining inside the boiler, has solved the so-called problem that "the water is not fresh for too long".

On the other hand, there are espresso machines with special water boilers. The temperature of the water and the steam pressure can be adjusted separately, and the temperature stability of its outlet head is the best I have ever seen until the time I wrote this book. It may be because the temperature control technology is better.

Pump pressure is stable

When cooking, the pump pressure should be stable. The modern pump can increase the pressure of the inlet to 9 atmospheres of the outlet. Basically, it can be divided into two categories:

* Rotary pump

* hydraulic drive piston type

The piston style is a waste of water. Each time you cook, you have to draw more water to achieve the required pressure. The rotary pump machine seems to be more suitable for most uses.

I don't recommend the old-fashioned piston lever machine, which pressurizes water by exerting force on a lever handle. But the pressure of most of this antique design is unstable, and if you cook a lot, the bar guy's hand will keep pulling, resulting in overwork. It is easy to cause "complications of wrist tunneling", which is very painful. Besides wrists, elbows and shoulders, they are also easy to get hurt.

Steps of "prepreg"

The espresso machine should have the function of "pre-impregnation". The espresso machine had better fill the coffee powder with saturated water before starting the main extraction step. This action is called "prepreg" and must last for 1 to 2 seconds. In a machine with a "pre-immersion" function, it will take 5 to 8 seconds before the coffee liquid flows out after turning on the brewing switch.

"prepreg" is very important. First of all, it can reduce the adhesion of soluble aromatic oils, making it easier to extract more oils. Second, it helps to close the top of the coffee filter cake, so that when the high-pressure water rushes over, it will not rush out of the hole, resulting in uneven extraction.

The pressure and dryness of the steam remain unchanged, and it is easy to operate.

Can supply constant pressure and dryness of steam, man-machine interface should be easy to operate. For detailed milk-beating techniques, see Chapter 18 of this book. The quality of steam is the characteristic of the machine, and the quality of the milk is greatly affected by the dryness of the steam. The volume of the steam chamber in the upper half of the steam boiler determines the dryness of the steam.

The steam boiler has a transparent window to check the height of the water surface. When the height of the water surface reaches exactly half the height of the window, the steam quality is the best.

Modern double (multi) boiler machines have automatic water intake devices to maintain the amount of water in the steam boiler and the volume ratio of steam to water. Before you buy a machine, do an experiment: try to see if it enters the water very frequently. Does the height of the water surface change very little? Or does it have to wait for the surface of the water to fall a lot before it automatically enters the water?

Most machines have a detector at the top of the steam boiler. In my personal experience, this control system performs very well in maintaining a constant water surface, and it is easy to adjust.

Semi-automatic and fully automatic machines

We freaks all prefer semi-automatic machines to fully automatic machines. I would like to thank Kent Bakke, the machine agent, for ordering this machine which looks a little out of date for us.

What is a semi-automatic machine? All you have to do is press a switch, start the pump, turn off the pump, that's all. It is important to manually control the amount of cooking per cup.

The faceplate of a fully automatic machine has a bunch of programmable function keys. The cook presses the appropriate selection button to let the machine decide how much water to boil, and automatically turn off the pump. If there is a large amount of cooking, a complex working environment (like in a restaurant), and high bar staff turnover (or poor training), the quality stability of cooking with a fully automatic machine will be better.

Automatic machine always works: grinding, filling, milking, finishing! You can have coffee.

.. Please! Instead of drinking this kind of coffee, buy a can of coke or swallow caffeine pills.

In order to pay attention to efficiency, we Americans have ruined a little romance in life. I know you bought this book to study technical issues, but I tell you, I think a good cafe should be a popular place, coffee history and cultural heritage are inextricably linked. When you go to a cafe, in addition to drinking coffee, what is more important is the interaction between people. Of course, this is just the prejudice of my old antique.

Purely technically, a skilled bar cooks better than a fully automatic machine. The fully automatic machine cooks better than the novice at the bar. The machine is great, of course, but it can't be controlled to maintain a certain extraction rate and a high level of milk foam.

Don't forget, check the man-machine interface.

Do you have a manometer? Do you have a boiler pressure gauge? When you look at these pressure gauges, do you find the position difficult to read? Do steam rods and control switches work smoothly? Is it easy to use? Does the switch button look durable? Or is it stingy and vulnerable? If you have an old bird at the bar, ask him to see if the operation interface of the machine is well done.

This chapter is summarized as follows:

"when you evaluate different machines, please refer to the key points described in this article to judge for yourself. don't pay for a certain brand of machine just because someone strongly recommends it." Most good companies will constantly improve their machines, understand the characteristics of various designs, and make their own decisions, so that they will not get lost in the colorful business promotion.

Selected from: ESPRESSO COFFEE: Professional Techniques 1996