To the layman, this may seem trivial, but each variation of the boiler (and heat exchanger) will produce a different way of working.
If you have your own manual espresso machine, or at least are familiar with espresso machines, you must have heard about the boiler features contained in these machines. If you don’t understand, a boiler is a container or tube – usually made of metal – that is in manual espresso machines.
The way it works, the water in the water source or reservoir will be flowed into the boiler and then be heated to a certain temperature as needed, whether for making espresso or for frothing milk. If you want to make espresso, the temperature required is generally slightly below the boiling point, around a maximum of 95°C. Meanwhile, if you want to froth milk (to make cappuccinos, lattes, and other espresso-based), all you need is steam pressure. Or familiarly known as, steam. This vapor pressure can be generated when water is heated to a certain temperature. For milk frothing, the heated temperature is usually below 71°C.
The problem is how can this boiler produce two different temperatures at once? Alright, let’s try to review one by one.
How Single Boiler, Double Boiler, and Heat Exchanger Works
Single boiler
An espresso machine that has only one boiler (single boiler), such as the Saeco Aroma espresso machine to Rancilio Silvia, users cannot perform the extraction and steaming processes at the same time. Because the boiler in it is only one unit.
Machines with single boilers are good enough for making espresso, but if you want to make espresso-based drinks that involve a mixture of milk such as cappuccinos, lattes, and others, the process must take turns. Preferably, do the extraction process first, then steaming. Because if you steam first, the temperature will already drop and generally tend to be unstable for the next espresso extraction process. For your information, after doing one process, the boiler generally has to neutralize the temperature first to zero before starting a new heating process.
Pros: the price of single boiler machines is generally not too expensive. Suitable for those who want to open a cafe with an economical concept. This type of boiler is also mostly portable, so the machine is easy to carry anywhere.
Cons: single boilers require a few minutes between extraction and steaming. In other words, this machine will take a little time if we want to make cappuccinos and other espresso-based drinks. Therefore, this boiler-type espresso machine is not suitable for use in busy shops, or those with a large number of customers every day.
Double boiler
As the name suggests, this espresso machine with a double boiler option—sometimes called a dual boiler—of course, has two separate boilers. One special boiler functions to maintain the extraction temperature (brewing), and the other is specifically for the steaming process. Therefore, this type of espresso machine generally has a stable temperature. Both boilers can also be used at the same time, so the machine can work more optimally and faster. Breville dual boilers and all La Marzocco series are examples of coffee machines that have this feature.
Pros: almost all espresso machines with double boilers have to control buttons and separate digital timers that are easily accessible, making it even easier to set the temperature for each brewing and steaming process. Because it has two boilers, the temperature becomes more stable, the engine can work more optimally and optimally. This is why machines with a double boiler feature like this are very suitable for use in shops that are busy, quite crowded, and have many customers every day.
Cons: the price is quite expensive often makes potential buyers feel expensive first. Lol. But isn’t the price generally worth the quality?
Heat exchanger
A heat exchanger is an additional feature found in certain types of single boiler espresso machines. So not all espresso machines with single boilers have this feature. How to mark it is quite easy. There is some kind of pipe or tubing that goes through the boiler, either at the top or the bottom, inside the boiler. This tubing is called a heat exchanger.
Heat exchangers are designed so that the water used for the extraction process is not heated in the boiler—unlike systems in single or double boilers. If you need water at a certain temperature to extract espresso, for example, then the water will be drawn into the machine by taking it from the tubing or this heat exchanger. In this tubing, the water will then be heated according to the required temperature. The Nuova Simonelli series and the Orchestrale Nota are some examples of machines of this type.
Pros: the function of the heat exchanger is almost like a dual boiler. This feature is considered to be able to help “lighten the work” of the boiler so that it does not have to do brewing and steaming at the same time. Some coffee enthusiasts find heat exchangers also great for keeping water from being kept in the boiler for too long.
Cons: the heat exchanger system is quite often questioned for its consistency in maintaining the temperature. There are also those who think that if used for a long time, the heat exchanger is no longer able to maintain a consistent temperature for extraction.
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