Test Drive: The Fellow Prismo

The Prismo cap attachment for AeroPress helps you brew an immersion-style coffee without flipping the device upside down.


Photos by Katrina Yentch

Many coffee professionals and home-brewing geeks typically brew their AeroPress through the inverted method, in which they flip the vessel upside down before plunging the coffee through its filter. As an immersion brewing method—when all water comes into contact with all coffee grounds at the same time—it creates a more balanced flavor profile, but it can also be a bit of a literal hot mess if not sealed properly. This is where the Prismo from Fellow Products comes in.

The Prismo comes with a metal filter that has a 70 micron etching.

In replacement of the cap and filters from AeroPress, Fellow’s Prismo is a little gadget that gives you an immersion-style brew without the instability of the inverted method. As Fellow explains the product, it is “a pressure-actuated valve designed to be used with the AeroPress Coffee Maker.”

Fellow claims that this product can create even more pressure within the vessel to resemble an efficient espresso-style cup of coffee. Because coffee usually begins to filter immediately after pouring water with the traditional brewing method, inverted is a preferred choice. However, inverted usually results in a little leaking, too; The Prismo’s no-drip seal, made possible by a gasket (just like what we see on an actual portafilter making espresso), is what allows the Prismo to replace this method. Furthermore, a 70 micron etched metal filter is also part of the attachment, which eliminates the need for a paper filter.

Once you insert the filter into the cap, it’s ready to be attached to the bottom of the AeroPress, ensuring further security.

Despite the fact that this product has been out since 2017, I’m baffled as to why I only recently discovered it—as its convenience reveals itself to me in several ways.

When dumping grounds from an AeroPress, I find that it can sometimes be a little too hot to pop out right after brewing. However, the Prismo’s mixed materials of silicone and polypropylene keep the product touch-safe and make it easy to dump grounds right away.

The coffee filters through the metal and the gasket, which makes a clean-tasting cup of coffee.

I’ve also made countless mistakes with my AeroPress. I’ve forgotten to add the paper filter and have experienced leaking down the sides when brewing with the inverted method, even when I’ve used a cup with a wide enough rim (which can sometimes result in under-extracted coffee brewing into the cup). Because there’s a metal filter in replacement of paper, it’s pretty noticeable when the filter is gone—the rest of the Prismo is just an empty cap with the singular gasket.

And hurrah! There was no leakage down the sides. Since the Prismo’s gasket dispenses the coffee, unlike the traditional cap with multiple holes, you can brew over cups as small as espresso shot glasses. (As a disclaimer, you should also change your ratio to reflect this. The circumference may be small, but so is the volume of the glass!) I was also surprised by how much easier it was to plunge the coffee. When I brew inverted, I sometimes end up having to press harder due to the extra pressure caused by flipping it upside down. The plunge with the Prismo, however, was quick, smooth, and clean.

Plunging is way easier to do with the Prismo, unlike a regular inverted-style brew.

One element I was especially curious about was the incorporation of a metal filter into the cap. Would it be as clean of a taste as an AeroPress made with a paper filter? I haven’t tried other metal filters currently on the market, but I imagine that they probably result in a heavier body from coffee oils not filtered by paper. It proved to have little effect on the taste for two reasons—the metal filter’s etchings are very small, and any fine coffee grounds that go through it have to go through the gasket, too. In this sense, the coffee sort of goes through two filtration processes within the Prismo, ensuring a super-clean and bright flavor. There was hardly any sludge at the bottom of my cup.

My only complaint would be that coffee tends to stick to the metal filter, which makes it hard to dispose of the entirety of the coffee puck directly into the compost bin. I thus ended up composting about 75% of the coffee grounds and scratching out the remaining amount into the sink, but I suppose going paper-free on coffee brewing outweighs that, right?

At a price of $25 for the Prismo, the amount of money you save on omitting paper filters makes this an affordable and convenient addition to your AeroPress. It’s also another great way to be more environmentally friendly about your coffee brewing. I’m excited to continue getting immersion brews without the leakage.

About Katrina Yentch 221 Articles
Katrina Yentch (she/her) is a freelance writer and Barista Magazine's Online Editor. When she's not writing, you can find her napping, cooking, and drinking whatever's on drip.