What is a brew unit?
A brew unit is the part of a coffee machine where the ground coffee comes into contact with the hot water, and the actual extraction takes place.
The term is used especially in relation to fully automatic coffee machines, where the machine grinds the coffee beans itself, doses the coffee, feeds it to the brew unit, and, after brewing, sends the used coffee on to the coffee grounds container.
The brew unit is therefore a central part of the process from coffee bean to finished cup.
How the brew unit works
When you select a coffee on a fully automatic machine, the process typically begins in the built-in coffee grinder.
The machine grinds a specific amount of coffee beans and feeds the ground coffee into the brewing chamber.
Here, the coffee is compacted, after which hot water is forced through the ground coffee under the conditions the machine is designed for.
The soluble substances from the coffee are extracted into the water, and the finished coffee flows out through the machine's coffee outlet.
After brewing, the brew unit opens again, and the used coffee is sent on as a compressed coffee puck or portion of coffee grounds.
The process can take place in just a few seconds and is repeated every time the machine makes a new cup.
The brew unit is part of a larger system
The brew unit alone cannot determine how good the coffee will be.
In a fully automatic coffee machine, several components work together.
The coffee grinder, among other things, determines how finely the coffee beans are ground. The dosage determines the amount of coffee. The water temperature, water volume, and the brewing process affect the extraction.
This means that a bad cup of coffee is not necessarily due to the brew unit itself.
Coffee beans, grind setting, machine setup, and cleaning can also have a major impact.
If you want to understand the entire process, you can also read our explanation of what bean to cup means.
Is the brew unit the same as an espresso machine's group head?
Not quite.
On a traditional espresso machine, the user places the ground coffee in a filter basket in the portafilter themselves. The portafilter is then locked into the machine's group head, and the water passes through the coffee puck.
On a fully automatic coffee machine, a larger part of this process is performed inside the machine.
Here, the brew unit is usually a mechanical unit that receives the ground coffee, forms a brewing chamber, and subsequently handles the used coffee.
The principle is the same in the sense that hot water must extract substances from ground coffee, but the construction and workflow are very different.
If you want to work more manually with espresso, you can read our guide to better espresso.
Can the brew unit be removed?
That depends on the coffee machine.
On some fully automatic coffee machines, the brew unit is designed so that the user can take it out and clean it.
On other machines, the brew unit is permanently mounted, and cleaning takes place through the machine's automatic programs or according to the manufacturer's instructions.
One design is not necessarily better than the other.
The most important thing is to follow the instructions for the specific coffee machine.
Do not attempt to remove a fixed brew unit unless the manufacturer specifically describes that it is intended for this purpose.
Why does the brew unit need to be kept clean?
Coffee contains oils and fine particles that can gradually build up on the parts the coffee comes into contact with.
In a fully automatic coffee machine, the brew unit is used over and over again, and proper cleaning is therefore important for both the function of the machine and the taste of the brewed coffee.
Where and how the brew unit should be cleaned depends on the machine.
If the brew unit is removable, the manufacturer will typically describe how it should be rinsed or cleaned.
If the machine has automatic cleaning programs, these should be performed according to the manufacturer's recommendations.
Only use cleaning or lubricating agents that are suitable for the specific machine and the task in question.
You can find maintenance products under cleaning and descaling of coffee equipment.
Does the brew unit need lubrication?
Some removable brew units require lubrication of certain moving parts at regular intervals.
Others do not.
There is therefore no single general rule that applies to all coffee machines.
Always follow the manufacturer's instructions.
It is also important only to use a lubricant intended for this purpose.
What is a coffee puck?
After the water has passed through the ground coffee, the used coffee remains.
In many automatic coffee machines, this coffee is pressed out of the brew unit as a compact portion, often called a coffee puck.
How firm or wet this puck is can vary between different machines, coffee types, dosages, and settings.
A wet coffee puck therefore does not automatically mean that there is something wrong with the coffee machine.
The taste in the cup and the machine's normal function are more important than the appearance of the puck alone.
What impact do the coffee beans have?
The brew unit can only work with the coffee it is supplied with.
The choice of coffee beans therefore has a major impact on the result.
Roast level, flavor profile, the age of the coffee, and the grind setting can all affect the finished cup.
If you use a fully automatic coffee machine and would like a classic, full-bodied coffee, you can, for example, take a look at our coffee beans for espresso.
However, this does not mean that all fully automatic machines require one specific roast level. The taste of coffee is personal, and machines function differently.
The brew unit is the coffee machine's workspace
The simplest way to understand the brew unit is therefore to view it as the place in the automatic coffee machine where ground coffee and hot water meet under controlled conditions.
The grinder prepares the coffee beans.
The brew unit brews the coffee.
And the machine's other systems take care of water, temperature, dosage, and handling of the coffee grounds.
If you want to see the various machines and brewing methods gathered together, you can proceed to our coffee machines and coffee brewers.
About Brændeholm Risteri's coffee knowledge
At Brændeholm Risteri, we work with coffee, brewing, and coffee equipment. You can read more about the roastery and the person behind it on the page About Brændeholm Risteri.