When an espresso doesn't taste good, we often look for the cause in the coffee beans, the grind, or the amount of coffee in the filter basket. This is logical, as these factors significantly influence extraction.
However, one factor is regularly overlooked: temperature stability.
But what exactly is temperature stability? Why do manufacturers of premium espresso machines pay so much attention to it? And how much difference does a few degrees really make in your cup?
What is temperature stability?
Temperature stability means that the water remains as consistently as possible at the same temperature during espresso preparation.
That sounds simple, but an espresso machine has to deal with various heat losses. Water flows from the boiler to the group head, comes into contact with metal, and loses heat along the way. If a machine doesn't compensate for this properly, the temperature can change during extraction.
A temperature-stable machine minimizes these fluctuations as much as possible.
What is the ideal temperature for espresso?
Most espressos are brewed between 90°C and 96°C.
However, there is no universal perfect temperature. That depends on the coffee you are using.
- Light roast: often 93°C to 96°C
- Medium roast: often 91°C to 94°C
- Dark roast: often 90°C to 92°C
Lighter roasted coffees are harder to dissolve and usually benefit from slightly higher temperatures. Darker roasts release flavors more quickly and can become bitter at high temperatures.
The ideal temperature thus varies per coffee, but stability always remains important.
How does an espresso taste at different temperatures?
A temperature difference of just a few degrees can already affect the taste.
Too low temperature
- More acidity
- Less sweetness
- Thin body
- Underextraction
Too high temperature
- More bitterness
- Less freshness
- Drier mouthfeel
- Risk of overextraction
Stable temperature
- More balance
- Better sweetness
- More consistency
- Predictable results
Why is an E61 group head so popular?
Anyone who delves into espresso machines will sooner or later encounter the E61 group head.
This group head was developed in 1961 and is still popular today. This is mainly due to heat management.
An E61 group consists of a large block of brass that can store a lot of heat. In addition, a thermosiphon system ensures that hot water continuously circulates through the group head.
This keeps the temperature relatively stable, even when multiple espressos are brewed in quick succession.
That is one of the reasons why many machines from brands like ECM and Profitec still use an E61 group.
What does a PID control do?
A PID is an electronic temperature controller.
Previously, many machines worked with simple thermostats that only reacted when the temperature had already significantly risen or fallen. This led to larger fluctuations.
A PID continuously measures the temperature and corrects deviations immediately.
The benefits:
- More accurate temperature control
- Fewer fluctuations
- More control
- Reproducible results
For home baristas, this mainly means that a well-tuned espresso is easier to consistently taste the same.
Is a dual boiler always more stable?
Not always, but often. Broadly speaking, there are three popular systems:
Single boiler
A boiler for both coffee and steam.
Advantages:
- Compact
- Affordable
Disadvantages:
- More temperature changes
- Waiting between espresso and steaming milk
Heat Exchanger (HX)
A steam boiler with a separate heat exchanger for espresso.
Advantages:
- Espresso and steam simultaneously
- Good temperature stability
Disadvantages:
- Less precise than dual boiler
Dual boiler
Two separate boilers.
Advantages:
- Maximum temperature control
- Very stable
- Many adjustment options
Disadvantages:
- Higher purchase price
Why is warm-up time important?
A common mistake is thinking that a machine is ready as soon as the light goes out.
The boiler may be at temperature while the group head is still relatively cold.
Especially machines with an E61 group often need 20 to 30 minutes to fully reach operating temperature.
Only then are all components sufficiently heated to deliver a stable extraction.
How do you notice at home that your machine is not temperature stable?
A machine doesn't have to be defective to show temperature fluctuations.
Signs can include:
- The same coffee tastes different every day.
- The first espresso tastes different from the second.
- You constantly have to adjust your grind.
- The taste varies without a clear cause.
When beans, grind, and recipe remain constant, but the results vary greatly, temperature may play a role.
Our perspective at FREKKO
Many coffee lovers first focus on coffee beans or a better coffee grinder. We completely understand that, as that's often where the most improvement can be made.
But once that foundation is solid, temperature stability becomes increasingly important. Not because it's an impressive specification, but because it helps to brew the same quality espresso every day.
And ultimately, that's what you want: not just a perfect espresso, but a perfect espresso every time.
