Are dual boilers the secret to a better cup of coffee?
Tanya Nanetti speaks with Bellezza founder, Alexander Lösch, about the virtues of dual boilers when it comes to making the perfect espresso.
When the first dual boiler espresso machine arrived on the scene in the 1970s, it changed the game for both home and professional baristas.
Operating with two independent boilers, it suddenly allowed the barista to heat the water and the milk separately – something that wasn’t possible with a single boiler system.
This means that while one boiler reaches and holds pressure ideal for steaming milk (between 110°C and 130°C), the other maintains a consistent brew temperature (between 88°C and 96°C).
The option to do both tasks at once not only saves time, but also produces better milk-based drinks, as there is no delay between brewing the coffee and steaming the milk.
This is in contrast to heat exchanger espresso machines, which have just one boiler. Instead, they use a copper pipe that passes through the boiler where cold water is pulled through and then heated to the right temperature to pull the espresso shot.
Alexander Lösch is the founder of Bellezza, a German brand of home espresso machines. He explains that one of the biggest advantages of dual boilers is that it gives baristas greater control over the machine.
“The dual boiler espresso machine helps to control the perfect and variable shot temperature, same as the single boiler,” he says. “But it also has the option to set a higher or lower steam power.”
Heat exchangers also allow baristas to pull a shot and steam milk at the same time. But unlike the dual boiler system, there is no direct control over the brew water temperature. In other words, there is no way of adjusting the steam pressure without having an impact on the brew water temperature.
Unlocking the coffee’s flavour
To brew a perfect cup of espresso, every coffee needs the right temperature to help extract all the inherent flavours. If it is too hot, it can burn the coffee and create bitter flavours, whereas if it is too cold, it will enhance sourness.
Once a barista has dialled in the ideal temperature for the coffee, it is important, therefore, to ensure it is kept constant between each cup.
This is where the dual boiler system comes into play. The two independent boilers and other features such as the PID temperature controller – an instrument that helps to accurately control the temperature using an algorithm – offer baristas better control over the temperature of the brew.
Alexander says that with so many new coffees now available, this ability to precisely control temperature for each one is essential.
“There are more roasters on the market right now than you can count,” Alexander says. “And many more are coming every day, each one bringing us coffees with more exciting flavours. Different flavours need a different temperature, but what they all have in common is the need for stability.
“And in the end, the stability of pressure and temperature is what makes the difference between a perfect espresso and a bad espresso.
“In my opinion the dual boiler is not only perfect for the professional barista, but it is also the best choice for the newcomer. Why? Because they can set the perfect temperature for espresso, while at the same time lower the steam pressure. In this way, they can get used to the latte art, while learning how to improve their skills.”
What else is needed for the perfect espresso?
While temperature is a key factor when making espresso, there are a number of other factors involved in achieving the so-called “God Shot” – the perfect shot of espresso.
First, a good coffee is essential. This means not only sourcing quality beans, but ensuring they are roasted to suit the brew style and properly stored to maintain freshness right up until consumption.
Unlike filter coffee, espresso relies on fast extraction – typically between 25 and 30 seconds per shot. As such, a medium-to-dark roast coffee is often better than a light roast, as a longer roast time tends to increase the ratio of soluble compounds.
Equally important is the quality of the water used to brew the coffee. Coffee is around 98.75% water and, consequently, has a considerable influence on the final cup.
According to the Specialty Coffee Association (SCA), the optimum water hardness for brewing coffee should be between 75ppm and 250ppm. Going below this range can lead to a “weak” coffee, whereas going above it can produce unpleasant astringency.
Once you have the right coffee and water, the barista’s skills naturally come into play, from finding the right grinding size to choosing a recipe that highlights all the qualities of a particular coffee. It’s also crucial to use the right equipment, including a good quality tamper and distributor.
In combination with these factors, a dual boiler espresso machine can help baristas – both at home and in a café – to prepare the perfect cup of coffee.