Portafilters, baskets and tamping tools

Why Does a Bottomless Portafilter Spray Coffee Everywhere?

Published · By the Espresso Shortlist editors · Prices and specs as of that date, from the pages under Sources

Summary

The spray comes from water moving faster through one part of the puck than the rest. Flair traces it mostly to channeling, caused by too little coffee, a grind that's too coarse, or grounds spread unevenly, and says the spray doesn't mean the portafilter is faulty. A second cause, bean fragments partly blocking a hole in the basket, is harder to prevent.

Two ways a jet forms

Channeling happens when water finds an easier path through the coffee bed, often because distribution or tamping left some areas looser than others. Flair's brewing guide describes the result as higher-velocity streams that "usually result in sprays or sprites emanating from the underside of the filter screen." With spouts attached you never see them. Brewing bottomless, you notice them quickly, because they hit the counter.

The other cause is a fragment of bean partly covering one of the basket's holes. Flair compares it to putting your thumb over the end of a garden hose. The stream leaving that hole gets faster and travels farther. Flair's view is that "there's little we can do about partial occlusion," while channeling can be reduced. The guide, written for Flair's manual presses, adds that easing off the pressure for a moment when a jet appears is sometimes enough to clear the fragment or close the channel.

What Flair suggests changing

Flair's support page lists the fixes in the same order as the causes. Use more coffee, grind finer, and use pre-infusion. A WDT tool can break up clumps in the bed. Pre-infusion, in Flair's description, means wetting the puck at low pressure, around 1 to 2 bar, for about 8 to 10 seconds before going to full pressure. Some machines do this for you, and the Breville Bambino, for example, starts every shot with low-pressure pre-infusion before 9 bar extraction.

Flair also sells paper filters that sit in the bottom of the basket before the coffee goes in. The listing says they reduce spray from bottomless portafilters and let coffee flow more evenly through the basket's holes. They come in two sizes, one for the Flair 58 family ($9.99) and one for the Classic, NEO, and Pro ($6.00).

Breville's guide to portafilter types says a bottomless portafilter lets you spot channeling as it happens, but it is "more prone to splashing" and "might not be the best choice for beginners." Breville's own naked portafilters, in 54 mm and 58 mm at $99.95 each, are sold as a way to "visually diagnose and troubleshoot your extraction."

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Sources

  1. Flair Espresso — How do I identify, prevent, or address channeling?
  2. Flair Espresso — Advanced Techniques, Brewing Naked or Bottomless
  3. Flair Espresso — Paper Portafilter Filters
  4. Breville — What are the different types of portafilters?
  5. Breville — the Naked Portafilter 54 mm
  6. Breville — the Naked Portafilter 58 mm
  7. Breville — the Bambino (BES450)

We have not tested these products. Specs, prices, stock and terms are as published on these pages on the date above and can change; check the manufacturer or retailer before you buy.

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