I love information. I like knowing how something works, the steps in the making of something- I feel like it informs my process. So, knowing how a portafilter works means I make better espresso. This is what I tell myself, at least.
Portafilter handles come in different materials and shapes, which makes them heavier or lighter and can affect how they balance in your hand during use (something to consider if you have multiple people using the same machine). Portafilter handles and baskets aren't generally interchangeable between brands, and often have slightly different sizes, shapes, and even hole patterns in the baskets. One of the most obvious differences in portafilters, though, is spouts versus bottomless.
Before getting into the details, it helps to know a bit about extraction works. This is the most barebones version of the brewing process; don't look for nuance here. As you “pull” a shot, a pump forces water into the group head and through a puck of finely ground and tamped coffee. The basket and handle together are the portafilter (portable filter).
The amount of pressure exerted onto that coffee can vary (how much coffee in the basket, how tightly its been tamped, the water temperature), but in an ideal world, it’s 8 to 9 bars. The water goes through the ground coffee and magically transforms into the espresso that fuels your day.
In a single spout, there’s a little diverter that directs the resulting coffee into one cup. Generally used for a single “dose” or shot of espresso. I don’t think I’ve ever made just one shot, as it’s such a small amount of coffee I find it hard to control and get good results.
In a double spout (for those double shots), you can brew espresso into two cups at once. Very nice if you’re making a drink for yourself and a friend.
In a bottomless portafilter, also known as a naked portafilter, there are no spouts, no diverting, just the filter basket with its teeny tiny holes.
For those chasing the perfect shot, I find using a bottomless portafilter means I can watch the espresso in the brewing process, which can tell me all kinds of things that I wouldn't know if there were spouts blocking my view.
Channeling (when water goes through the puck unevenly as your espresso brews) is obvious as soon as it happens- meaning one (or many!) things need to be adjusted.
Maybe the distribution of grounds was off, or the tamping was uneven, or the grind size was too fine or too coarse. Maybe the dosing was incorrect for the basket.
Any operator error is made clear with a bottomless portafilter, resulting in sprays and/or a messy extraction. But the learning process goes faster when you can see what needs correcting.
Of course when the shot immediately comes together at the center and those beautiful tiger stripes start forming- well, that's pretty satisfying. Bottomless portafilters are perfect for showing off barista skills.