Bottomless (Naked) Portafilters

Bottomless portafilters look exotic when brewing espresso, and have a cult following among baristas. There also are practical reasons to use these. If you have a home espresso machine, here’s why you might want one of these among your accessories.

What is a Bottomless Portafilter?

A bottomless (naked) portafilter is a portafilter that has no spout on its underside. Whereas traditional portafilters have either a single or double spout, the bottomless one has nothing. It doesn’t even have a bottom that funnels the brewed espresso through a hole — espresso directly exits the basket screen and goes into the cup.

Bottomless portafilters are sometimes called naked portafilters, because the basket is “naked” and can be seen.

A bottomless portafilter is not pressurized. We have a guide about the differences between pressurized and non-pressurized portafilters, if you’re wondering.

Bottomless vs. Spout Portafilters

Traditional portafilters have either a single or double spout through which brewed espresso flows. The design stems from Italian coffee culture, where single (the default) and double espresso beverages are both commonly drunk.

Many specialty coffee shops outside of Italy use double shots as their default, and therefore have only double-spouted portafilters. While a single spout theoretically can (and sometimes is) used for a double espresso, the practice is uncommon.

Bottomless portafilters differ from both of these, in that bottomless portafilters have no spout at all. The naked design results in several differences that are relevant to home espresso.

Advantages and Disadvantages of Bottomless Portafilters

The lack of a portafilter spout simultaneously presents advantages and disadvantages. In short, bottomless portafilters are beautiful, educational, slim and messy.

The various benefits and drawbacks fall into three categories: aesthetic, educational and practical.

Aesthetics: Naked Portafilters Look Beautiful

At least one kind of nakedness is aesthetically desirable when pulling espresso. There simply is no matching the beautiful elegance of correctly pulled espresso as it flows out of a bottomless portafilter. 

The brewed espresso flows along the screen to the basket’s center, where it then steadily flows into the cup. The patterns are mesmerizing, especially if you bend down to see the bottom of the naked screen.

There’s a reason why cafes often use bottomless portafilters when taking pictures, even if they don’t use the portafilters on a daily basis (see Practical). You too will want a bottomless portafilter if you’re vying to be a social media star, or if you simply enjoy the look of a perfectly pulled shot.

Educational: Naked Portafilters Show Grind and Tamping Issues

Because you can watch espresso flow directly from the basket, you can monitor how it flows from the basket. Different flow patterns reveal different issues with the grind and/or tamping:

Channeling

More espresso brews out of specific areas of the basket screen. This indicates that water is flowing faster through channels in the grounds, thereby creating uneven extraction and reducing extraction time.

Channeling can be caused by weak tamping or inconsistent grind size. Try using more force when tamping. If that doesn’t resolve the issue, the best remedy is to invest in a better grinder that’s able to produce more uniform grounds.

Pinning

A thin “pin” of espresso shoots out of one spot. This likely occurs after trouble pulling the shot and before the speed splashes and causes a big mess. Pinning most often occurs in only one place, although it can happen in several places at once. You probably won’t see it until after there’s a mess all over the counter.

Pinning is caused by the coupling of a very small channel and a high group head pressure. It might be addressed a few different ways:

• Sometimes pinning just randomly occurs. Pull another identical shot to see whether it happens again.
• The high group head pressure can indicate that the grounds are too fine, as water can’t adequately flow through them. The narrow channel is further indication that the grinds are too fine. Try redialing in the espresso, using a slightly coarser grind.
• A low-quality basket could have a poorly punched hole. The probability of a hole causing pinning is low, but possible. 
• Consistent pinning in the same spot would occur if the issue is basket-related, and you could confirm this with a visual inspection of the basket’s screen. The only fix would be to purchase another basket.

Donut Preinfusion

Espresso first flows in a “donut” ring around the outside of the basket, before filling in the rest of the screen as extraction continues. The donut may be whole or partial, depending on how even the tamp is.

Donut preinfusion is the result of side-channeling along the basket’s circumference. This can happen if the tamp is poor, the basket is wet when dosing, or the tamp itself is too small for the basket. Be more diligent when prepping espresso, and check the tamp/basket size if that diligence doesn’t resolve the problem.

Off-Center Flow

The downflow of espresso isn’t located in the center of the basket, but rather to one side. A perfectly prepared shot will flow from the direct center of the basket.

Off-center flow is almost always caused by poor preparation. The grounds were either unevenly disbursed in the basket or unevenly tamped. You may need more practice preparing shots, which is common for new baristas.

Rarely, off-center flow could be caused by an uneven espresso machine. The flow would always be off-center, but consistently in the same general spot.

Practical: Naked Portafilters Have Several Considerations

The practical implications of naked portafilters are some of the most factors for home baristas, and they include both good and bad aspects.

Quality

The cult following reminisces about mythical perfect shots that are heaven in a cup — and only replicable with bottomless portafilters. They don’t claim that every espresso shot from a bottomless portafilter is perfect, or even better than those from a traditional spouted portafilter. When that rare perfect shot is pulled from a bottomless portafilter, though, no other coffee compares.

Non-believers treat these tales of mythical shots as just that — myths. They say that there’s fundamentally no difference in the quality of espresso that’s brewed through bottomless and traditional portafilters. 

Despite what non-believers claim, there might actually be some science that supports the cult following of bottomless portafilters. 

Some espresso adheres to the side of a traditional portafilter’s spout, and this results in a little loss of crema. The espresso that flows off of a bottomless portafilter goes directly into the cup, thus causing no loss of crema. Crema does impact the flavor of a shot — so a shot with more cream may indeed taste better in some cases.

Overdosing

Overdosing is the practice of using more espresso than is typical when pulling a shot, in order to change the shot’s flavor profile, strength, volume or other characteristics. This is common practice with some home machines that have small portafilter sizes, and is occasionally done for other reasons.

Overdosing is only possible when using a bottomless portafilter, for a traditional portafilter’s bottom restricts how deep the basket can be. A bottomless portafilter is able to accommodate deeper baskets that hold several more grams of grounds.

Cup Clearance

Because a bottomless portafilter doesn’t have a spout, it has a smaller profile and leaves more clearance below it for cups. Clearance is a particular issue with many home espresso machines, as they tend to be smaller.

You can always pull shots into a demitasse cup, and then from the demitasse into a mug. This disturbs the crema and results in slight volume loss, however. Pulling directly into a mug that you’ll make a cappuccino, cortado or americano in may be preferable, and a naked portafilter might provide the clearance your mug needs.

Messes

The lack of a bottom and spout means that bottomless portafilters have nothing to contain the mess when a shot goes awry. Whether caused by pinning, a portafilter that’s loaded askew or just randomness (which does happen), a major problem will be a major mess. Be prepared to have grounds, water and espresso all over your kitchen, your clothes and possibly even your face.

Messes from missed shots are uncommon, but bound to happen occasionally. If you have fine art near your espresso machine or pull shots in the morning after dressing for work, this alone might be reason enough to stick with traditional portafilters — they have a bottom and spout to contain most messes.

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