The biggest questions I get from friends and fans of the channel is how to make their espresso not taste bad. 

This is an incredibly complex question, but in this video I talk all about how I diagnose espresso shots and make them taste better!

I highly recommend that you get a bottomless portafilter for diagnosing espresso. It is absolutely possible with a standard commercial double spout or single spout portafilter, but the bottomless one will let you see with your own eyes some elements that might be hard to diagnose when you can’t see (for example, not noticing channelling).

Diagnosing Espresso Flow Chart

Channelling

This is one of the most misleading variables that it is easy to misdiagnose. Channelling happens when there is too much pressure at the place where the water meets the puck, and is usually caused by grinding too fine or overfilling the basket. The water, looking for the path of least resistance, finds the weakest point in the puck (lower compression, less coffee) to push through, and will stream out very quickly. This leads to a lot of sourness even though the coffee might be hitting the right timings. Some ways to fix this:

• Look for a slow start that rapidly speeds up
• Try adjusting a little coarser and checking that you distribute the coffee with your finger or a distribution tool before tamping.