I think it was in 1991 that John Blackwelll showed me a bottomless porta-filter to play with. (John is a LaMarzocco engineer and has been a key figure in my ability to advance espresso coffee. I will never forget coming in in ‘94 all excited because I had figured out how to measure the brewing temperature on the coffee bed. I whipped it out my rig as he dove under his desk and I could hear rummaging…then he appeared with the exact thing, a Fluke KJ digital thermometer with the bead probe threaded up through a hole in the coffee basket. And…this is hardly an isolated occurence in our history…)
Anyway I played with the bottomless PF, marveling at the beauty of the coffee coalescing beneath the basket in perfect chaos until it formed into an undulating stream of crema.
I found it very useful for evaluating grinders and distribution techniques because any problem instantly showed up as excessive white streaking in under the basket.
At left is espresso made on a dull conical burr grinder. Note excessive streaking under the basket.
In 1994 I rejected this for bar use because baristi had trouble timing the pour compared to the old double spout. At the time I was dedicated to staff reading the coffee without the use of timers. However, with the advent of super machines, like the Synesso and LaMarzocco GB-5, flow rate became so critical that we went back to timers. (With temperature stabilized espresso machines extraction time is about 23-25 seconds for the double shot with no margin for error. Old machines were more forgiving and a 30 second pour was often as good as a 25 second pour.) Using timers again for shot duration and volume meant that we could adopt the bottomless PF for all machines at Vivace. It became clear in the last few years that bottomless PF’s produce better espresso coffee.
First there is the brass that the Italian PF is made from. Brass is a soft, porous metal that contains lead. Being porous it traps coffee in it’s surface where it becomes rancid and contributes th dirty-machine taste to espresso flowing over it. This taste is akin to chewing on dirty athletic socks and will not benefit your espresso. (At least I sincerely hope not.)
The bottomless PF eliminated an entire surface from being able to contaminate our coffee and produced a clean flavor profile inching ever closer to a quote of the fragrance.
(It is worth noting that LaMarzocco and Synesso both replaced the brass diffusion blocks with stainless steel. In general moving from brass to stainless anywhere in the brewing surface network makes your espresso have a cleaner, sweeter taste. Diffusion blocks are the masses of metal that your dispersion screens screw into.)
Another benefit we noticed is the very light weight making the barista job easier and more fun.
Drawbacks to the bottomless PF include not being very stable to pack coffee into compared to the old double spout. We hang the handle over the edge of the counter to obtain a flat, stable packing surface. Also, you are not able to serve a single or triple-shot as easily. (Remember, an espresso shot is stratified within the cup. No matter how hard you swirl the cup, the sugars hang around the bottom of the shot. So, you cannot just pour out half the shot and have a true single espresso coffee.)
Personally, I will not brew espresso on any PF except bottomless.