Sometimes when you make espresso, unbeknownst to you, the water will find an easy escape through the coffee instead of taking its time and going through evenly like it should. When this happens the water “channels” very quickly, hardly touching the coffee at all, and you’re left with a cup of weak, watery coffee. Ick.
Today BoingBoing linked to EspressoPorn.com (safe for work), a site about using a portafilter which has had the bottom removed. This allows you to see if the espresso is pouring out evenly from the filter basket as opposed to channeling through in one spot. Plus it looks really cool.
If you’re interested in learning how to use a bottomless or “naked” portafilter, check out this page on diagnosing your shots using a naked portafilter. You can purchase one from EspressoParts.com.