Many factors influence the quality of the final coffee brew. One of these factors is called "channeling." But what exactly does this term mean?
What does channeling mean?
Channeling occurs when the hot water doesn't flow evenly through the coffee grounds during brewing. Instead of extracting the coffee evenly, channels form in the coffee grounds through which the water flows. This leads to uneven extraction and therefore a poorer taste.
How does channeling occur during extraction?
Channeling can be caused by various factors, including an uneven distribution of the coffee grounds in the portafilter, a grind that is too coarse, or uneven tamping. Incorrect water temperature or excessive brewing pressure can also lead to channeling during coffee extraction.
Why is channeling problematic?
Channeling causes certain parts of the coffee grounds to be over-extracted while others remain under-extracted. The result is a coffee with an unbalanced flavor, which may taste bitter or sour. Therefore, to brew high-quality coffee, it is important to avoid channeling.
How can you prevent channeling in espresso?
The principle is simple! Water seeks the path of least resistance, thus forming a channel where the coffee grounds (cake) are more permeable than elsewhere. The solution is to prepare the coffee grounds in the portafilter before extraction so that they are evenly distributed and tamped.
Here's how to properly prepare the portafilter before extraction!
- Distribute (e.g., using a WDT tool)
- Knock
- Cancel
- Leveling (smoothing)
- Tampen (Stamping)
Once the ground beans are in your portafilter, gently tap it to distribute the grounds evenly and prevent clumps. Use a WDT tool, for example, to distribute the coffee grounds and break up any remaining lumps. Then, gently tap the portafilter again and scrape away any excess coffee grounds to prepare it for leveling.
For the final leveling, a Motta Leveler, for example, can help. With this barista tool, you can smooth the coffee grounds with a gentle twist. Now comes the last step: tamping. Make sure the tamper fits your portafilter: they come in different diameters (usually 58mm).
The same applies here: don't press too hard, but also not too loosely. Make sure that the coffee grounds are evenly compressed by tamping correctly and that you don't hold the tamper at an angle.