Which to Buy? Espresso machine single boiler or double boiler?
Here we shed some light on the differences between single and dual boiler espresso machines, as well as how to brew and steam efficiently with each type of machine.
If you are new to the world of espresso machines, then you have probably asked the question that this article is about — whether you should get one with a single (one) boiler, or one with double (two) boilers (also called dual boilers by some people).
This whole thing about boilers is, for most people just starting out, one of the most confusing things to get a good grasp on.
The main reason for this is because when one starts talking about the internal workings of a home espresso machine, it sounds very “techy” and intimidating. It really doesn’t have to be that way.
This “whole boilers thing” really is actually quite a simple thing to learn, even though it sounds very confusing when you first start looking for an espresso machine and see the jargon involved in the whole thing, which definitely includes a lot of talk about single and double boilers.
Important: Throughout this writing we will refer to “frothing,” foaming,” and “steaming” of milk.Frothing, foaming, and steaming all mean exactly the same thing when you are talking about making milk into that rich, creamy foam that you see in beverages such as cappuccinos. They are basically just two different interchangeable words that are meant to say “the heating of milk with steam to create froth for espresso beverages.”
What exactly is a boiler in a home espresso machine..?
The boiler (or boilers, in the case of double boilers – which will be explained later in this writing) is a sealed metal container inside an espresso machine that holds the water poured into the water reservoir on the outside of the machine.
The water poured into the water reservoir goes into the boiler(s), where it is heated to the temperature needed to be able to make espresso, as well as the needed temperature to produce steam in the milk frothing process.
Definition of Double Boiler Espresso Machines
Double boiler espresso makers, as the name implies, have in them two separate boilers (also called “dual boilers”). It is basically agreed by most, if not all, people that machines with double boilers provide the home barista with the best end result.
Machines that have double boilers normally also come equipped with each of the two boilers having its own individual control (heating thermostat), allowing one to heat water to a hotter temperature than the other.
The water that is heated to go through the ground coffee and extract the flavor from the coffee needs to be less hot than the water that is used for steaming milk.
If a machine with double boilers is used, both boilers can heat water simultaneously, with each boiler adjusted to the temperature needed for its particular function, whether it be steaming the milk or running through ground espresso beans to extract the espresso flavor.
Having a machine with double boilers not only ensures better results, due to using the correct water temperature for each needed function, double boilers also get rid of waiting between brews and steaming sessions.
With a single boiler, the water must be heated to the right temperature for extracting through the ground coffee. After that, there is a waiting period while the water heats up to a hotter temperature, which is necessary to achieve correctly steamed/frothed milk. This results in wait time, which a lot of people prefer not to have to do, particularly in today’s busy world of go, go go. This is the reason that so many people much prefer a machine that has double boilers over a machine that has just one.
There are other systems available with some espresso makers; however, the majority of them you will see have either one or two boilers as part of their water-heating system. Therefore, the subject of boilers is the only one that will be discussed in this page, at least for now.
For machines that have double boilers, below are definitions of the two different boilers, and what each boiler’s specific function is.
- Dedicated Brew Boiler – The boiler that heats the water for the coffee grounds:One of the two boilers is there simply to heat the water that seeps through the ground coffee and extracts the espresso down below into a waiting espresso cup or mug. This boiler heats water to a less hot temperature than the other boiler.
- Dedicated Steam Boiler – The boiler that heats water to be used with the milk-frothing wand:The other boiler of the two heats another, separate batch of water simply for steam (used for frothing milk with a milk steaming wand). This boiler heats the water to a hotter temperature than the other one.
Having two separate boilers prevents the water that is run through the grounds from being too hot and possibly scalding (burning) the ground coffee, while at the same time allowing the water that will be used for frothing the milk to reach an optimum (higher/hotter) temperature to allow for great steaming of milk.
Most espresso machines with double boilers have separate controls that are easily accessible, and many times digital, to allow the user to set each boiler to the optimal temperature for the function of that particular boiler.
How An Espresso Machine With Double Boilers Works
Below is a diagram that will help break down the basics of a machine with double boilers:
On the diagram above, note that although the thermostats we show appear to be located on the actual boilers themselves (which they are in a sense), most espresso machines have external controls on the outside of the machine, along with the other controls, that allow for setting your preferred temperatures for brewing and steaming.
Boiler Materials
Boilers for espresso machines are made of metal, due to the heat conductivity properties of metal.
The types of metals primarily used for espresso machine boilers include copper, brass, aluminum, and stainless steel.
- Copperis one very common metal used or boilers, due to its excellent capability to for holding heat, which results in a more stable water temperature. There are a good number of people who feel copper is their only choice when it comes to a boiler for an espresso maker. Most, if not all, traditional Italian espresso machines utilize copper boilers.
- Stainless steelis another material somewhat commonly used, although not as commonly as copper, due to the higher cost. Stainless steel also reportedly does not retain/hold heat as well as copper. A significant number of people feel stainless steel is more safe health-wise than copper.
- Brassis yet another type of metal used in the manufacture of boilers for espresso makers.
Most people who have used a number of different espresso machines have a preference for one type of metal boiler over the others.
Summary – Single or Double Espresso Machine Boiler – Which Is Best?
Double Boilers Summary
Most, if not all people who have used one or more home espresso machines agree that a machine with a double boiler is by far the best.
Although there are not a TON of reasons for this being the case, and rather just a couple of reasons, the couple of reasons for considering a machine with double boilers over one that has just a single boiler are very clearly obvious, once they are pointed out. They are as follows:
- No one likes to wait!A machine with double boilers allows you to pull an espresso shot while at the same time having “other” water that is sufficiently hot enough to produce steam for making milk froth, which allows for simultaneously steaming your milk at the same time your espresso is brewing.
A single-boiler espresso machine will require you to wait in between the time you have brewed up your espresso and the time when you will have milk froth ready to add to it. This wait time will be due to having to wait for the single boiler to heat up to the optimum temperature for steaming milk, which requires the water to be at a higher temperature than the espresso brewing step requires.
- Much more accurate water heating capability.Machines with double boilers are able to more accurately heat the water for both extracting flavor from grounds and that used for steaming milk into a rich, creamy froth. Lots of machines available nowadays come with digitally-controlled thermostats for the dual boilers in them, allowing you to heat each boiler to the perfect temperature according to what the water in that boiler will be used for.
Single Boilers Summary
There is truly just one reason we were able to ascertain for choosing a machine with a single boiler over one that has double boilers – cost.
Machines with single boilers usually cost much less than those with dual boilers.
We were not able to determine any other reason for choosing a machine with a single boiler over one that has double boilers.