All coffee machines that use pressurised water (capsule machines, manual espressos and automatic espressos) require the water to reach an optimum temperature so that the espresso comes out in good condition.
This temperature is around 93º-95º, although most purists will always discuss whether the extraction should be done a degree above or a degree below. It is not the purpose of this article to enter into that debate now.
The point is that espresso machines use two different systems to heat the water to this temperature: the boiler or the Thermoblock. Newer coffee machines are usually fitted with Thermoblock, which, as we will see later, is a more energy-efficient system and also cheaper. There are fewer and fewer coffee machines that use a boiler, although those that exist are usually of medium or high range.
In this article, we will explain what both heating systems consist of, what their advantages are, and what their fundamental differences are.
What is a boiler
Boilers are closed tanks or compartments that have resistance inside. This resistance is responsible for heating the water inside the boiler. The water remains inside the boiler at all times and only comes out when coffee is extracted.
They are usually 250cc, although there are models of coffee machines (generally very high range, semi-professional or even oriented towards small businesses) that mount 325cc boilers.
The boilers are usually made of aluminium, steel or brass. This last material is preferred by expert users due to its ability to maintain the temperature of the water but above all because of the doubts that aluminium offers when it generates waste over time. The disadvantage is that coffee machines with a steel (or brass) boiler are usually more expensive.
An example of an espresso machine with a brass boiler is the prestigious Rancilio Silvia.
What is a Thermoblock
The Thermoblock, or Thermoblock, is a system that does not store water but takes it directly from the tank and passes it through an intricate circuit or set of pipes. It is bypassing through this labyrinth that the water is heated. The process is carried out on the fly; at the moment, the user orders the coffee, and only the water strictly necessary for such service is used.
Although with a different concept, a Thermoblock system does precisely the same function as a boiler. The coffee makers with Thermoblock work externally in a similar way to coffee makers with a single boiler (which does not mean that inside they work the same, as our reader Javier points out in the commentary at the end of the article).
We won’t go into too much detail about this piece since you can learn more about the Thermoblock in this article, discussing it in more depth: What is the Thermoblock system?
Boiler vs Thermoblock: differences and advantages
Which is better, a boiler or a Thermoblock? Let’s try to shed light on this question by looking at the main advantages and disadvantages of each system.
Advantages of Thermoblock
To get to the point, and so that we understand everything more quickly: as we said before, the boiler is a watertight container where all the water inside is heated equally. The Thermoblock, on the other hand, consists of a small circuit (hence the winding tube appearance) through which only the amount of water needed to prepare a coffee goes through.
Not all the water is heated, but only the water to be used and it goes through the circuit. In this way, Thermoblocks are more efficient (they heat less water, ergo spend less energy and take much less time) and also do not use standing or accumulated water, but freshwater.
Coffee machines with a boiler need a longer “heating” time because all the water has to be heated, regardless of what we use afterwards. Double boiler coffee machines are even slower because both boilers (the one for making coffee and the one for the steamer) are heated equally, also if we don’t use the second one.
There are also coffee makers that use Thermoblock and have a vaporiser, of course. But these also have the advantage of heating the water for the steam only when the user asks for it, so there is also a slight saving there. Mild if we prepare only one coffee, but after tens or hundreds of coffees for sure the electricity bill will be quite different.
To do this, they use two different thermistors depending on the option we select in our coffee maker (prepare coffee or vaporise); one or the other will be activated. One thermistor will order the Thermoblock to heat the water to 93º, and the additional thermistor will order the heating to be taken to 124º.
The following diagram (in English but correctly understood) can better visualise how both systems work.
We see that the Thermoblock (in white) is an empty circuit, through which water enters and leaves. The boiler is already filled with water (in blue) and has a resistance inside (red line) that increases its temperature to the level that the thermistor tells it to:
Advantages of the boiler
What advantages do boilers have over Thermoblock? Mainly three:
1- The designs and manufacturing materials of the coffee machines with the boiler are usually more attractive and of higher quality, because stainless steel is the one that predominates. Although as a consequence, they are also often more expensive.
2 – A Thermoblock has a rather sophisticated internal design, and it is not easy to remove and repair it if it breaks down (it is usually replaced with a new one). At the same time, boilers are loose pieces that can be taken out of the coffee maker, fixed, polished, etc.
Although indeed, the general public does not care much about this type of detail, the ease with which boilers can be repaired at home and their breakdowns fixed is one of the reasons why many coffee enthusiasts and experts prefer them to Thermoblocks.
3 – The boiler ensures that all the water will get the same temperature in all conditions always. In a Thermoblock, this is not still the case, and most purists notice it.
For example: if the ground coffee is very pressed or the grind is excellent, the water will go through the block more slowly. It can cause it to get hotter than it should be. On the other hand, if the water passes through too quickly – too coarse, too little pressing, too small grinding – it will be slightly less hot.
Note, for example, that this detail will never occur in capsule systems or flexible single-dose systems (whose compaction, amount and thickness of grinding are always the same). That is why all coffee machines of this type usually have Thermoblock.
Coffee makers with a boiler
Both the kettles (present in older coffee machines) and the Thermoblock (which is gradually gaining ground in all modern espresso machines) serve the same purpose: to heat the water and reach an optimum espresso-making temperature as efficiently and, if possible, as quickly as possible.
However, if we look at most domestic espresso machines (both manual and automatic), they also include an accessory that serves to froth the milk and allows the user to make preparations such as cappuccinos, lattes, etc. at home. Steam is used to froth the milk, and for this reason, this accessory is called a vaporiser.
If we go over the physics lessons, we will remember the temperature at which steam is generated (around 124º degree up degree down), which is very different from the ideal temperature for making espresso coffee (between 93º and 95º).
This forces coffee makers with a frothing device to play with both temperatures and to have their boiler stop the resistance at two different levels: at 93º or 124º, depending on whether we want to heat the water for the coffee or froth the milk. And, of course, you have to wait for the temperature to rise or fall steadily.
Most domestic espresso machines have a single boiler with a heat exchanger. In this type of boiler, the temperature is always ready to steam (around 124º as mentioned above), and this temperature only changes when the freshwater passes through the heat exchanger tube. This way, you can make coffee and hot milk at about the same time (or at least without a significant delay) and with only one boiler.
Coffee machines with a single boiler (without a heat exchanger) are more basic and logically take much longer to make the transitions from coffee-making mode to milk-steaming mode and vice versa.
Coffee machines with two boilers
Some espresso machines go much further and directly include two separate boilers. One is dedicated exclusively to heating the water for the coffee (95º), and the other one heats the water to obtain steam to be able to use the milk vaporiser (124º).
Each boiler is always ready to perform the function it needs. There are no waiting times between processes and no changes in the resistances, although when the coffee maker is switched on, it will be necessary to heat more water than if there were only one boiler.
Naturally, espresso machines with a double boiler are more sophisticated and more expensive than single-boiler machines (which are much more common).
Some examples of coffee machines that use two boilers are the Saeco Exprelia Evo or the Saeco Royal:
As you can see, mainly high-end (and high-priced, too) super-automatics.
Conclusions: Thermoblock vs Boiler
In our opinion, and any expert will tell you this, the fundamental thing is to have good coffee – raw material – and a good grinder. Counting on this tandem and knowing how to use it well, surprising as it may seem, you can obtain a delicious quality espresso coffee, even if the coffee maker where you extract it has no boiler or heat exchanger.
From there on, the decision is up to each individual. We have already seen that the two systems work mostly the same (with their advantages and disadvantages) and that the differences between them do not always affect the result of the drink. And we have also seen that there are opinions for all tastes as many as there are coffee palates.
If you want to be entirely sure that the water temperature will be stable, opt for a coffee maker with a boiler (if you can afford it, a steel one, and if it goes even further better with two boilers). If not, the results with a Thermoblock coffee maker can be the same, and you can also save a lot of money (mainly on the coffee maker).