When you begin to learn coffee, the first thing you pick up is that every step in the process, even the smallest ones, are incredibly important. One wrong move or technique in the grinding process is going to affect how well you can evenly tamp the shot, a bad tamp will affect how the shot pours, how the shot pours is going to affect the taste, etc. you get the point.
One of these small steps that have a big impact on the overall coffee making process, is tapping the side of your portafilter when tamping. This technique has been taught in workshops, coffee shops & courses up until recently in the past few years when people started realising that it wasn’t a great thing to do. Some baristas today are still doing this technique – unknowingly preventing themselves from getting brilliant shots consistently.
Here’s why; tapping the side of your portafilter causes channelling. When you tap the side, the reaction from the coffee is to create a small wall of separation from the basket, which creates a channel for the water to go through instead of evenly distributing water and pressure over the entire coffee shot.
If you haven’t heard of the term ‘channelling’ before, I’ll explain a bit further. To get the perfect espresso shot, you place the portafilter in the group head and run the shot where an extreme amount of pressure and water is released, extracting the coffee from the grinds that were in the basket, right into your mug. But – water is lazy and will choose the path of least resistance when it has the opportunity to do so, and one of these opportunities is through channelling. When there is a gap in your coffee grinds, the water will instantly run to that gap because it means that it will need to cause less pressure and do less work – see, lazy! It gives an uneven extraction because that water and pressure is only going to the gap and not the other parts of the coffee, so what you’ll end up within your cup is essentially just hot water.
To recap – don’t tap the side of your portafilter, it causes channelling and prevents you from getting great shots. Work on breaking that habit and you will see improvements!