Method · Filters

Filter throwdown, part 3: reading the results

Filter comparisons are everywhere — forum threads, blog “throwdowns”, retailer round-ups. Most are honest; few are controlled. This page is a toolkit for judging them, plus a protocol for running your own side-by-side. It reports no results of its own.

1. Check what was held constant

A good comparison changes one thing — the filter — and keeps everything else fixed. The Home-Barista forum test of paper vs an IMS Superfine metal filter is a useful example: same coffee, same water minerals and temperature, same ratio, same inverted recipe (15 g coffee, 30 g bloom for 30 s, 160 g more water, 60 s wait, stir, press within 20 s), both cups brewed at the same time.

2. Know the numbers behind “fines”

AeroPress publishes the hole size of its stainless filter: 178 microns. It also describes typical particle sizes — espresso-style grinds around 300–500 µm with lots of material near 100 µm, medium grinds 800–900 µm with fines down to 100 µm. So a metal-filter comparison done at an espresso-fine grind is really a test of how many fines get through, not just of the filter. When a write-up does not state grind size, treat its conclusions on sediment and body with caution.

3. Was it blind?

Blinding — keeping tasters from knowing which sample is which — exists to reduce bias from expectations and confirmation bias. The forum group confirmed their tasting was blind and used cupping spoons. Commenters still asked whether sample order was randomised and whether tasters spat — fair questions that apply to any home test.

4. How many tasters?

The forum test used four tasters (two experienced with filter coffee, two new to it). One commenter noted that whether a result is meaningful depends on both sample size and how big the difference is. A strong, consistent difference may show up with few tasters; a subtle one needs many.

5. Separate measurements from impressions

None of the comparisons cited on this site measured total dissolved solids or extraction; they report sensory impressions. That is fine — but phrases like “stronger” or “more extracted” should be read as descriptions, not data.

A fair home protocol

1. Pick one bag of coffee and grind one batch at a medium setting so both brews share the same grounds.
2. Weigh dose and water for each brew; use the same kettle water for both.
3. Brew paper and metal one after the other with identical timings. Two AeroPresses make simultaneous brews easier.
4. Have someone else label the cups underneath, or shuffle them yourself, so you do not know which is which.
5. Taste hot, warm and cool. Note body, clarity, sweetness and grit before revealing.
6. Repeat on another day, and again with a finer grind — the metal filter’s result should move more than the paper’s.

Where this fits

For a plain-language summary of what each filter does, see paper vs metal, explained. For one specific metal disk, see the Able DISK Fine file. And because filters also change diterpene levels, the health angle is covered in metal filters & cafestol.