Coffee Data Science

Espresso Feasibility: Mesh+Paper on the Bottom of the Basket

An exploration for a paper on bottom variant

4 min readMay 28, 2024

Paper filters have been shown to improve espresso extraction, and in some recent explorations, someone on the EAF Discord suggested putting a metal mesh underneath the paper filter. I wanted to explore this across a few roast development levels in a controlled study. My results did not show an improvement, but that doesn’t mean the experiment was ideal, so let’s talk about it.

First, I made a metal mesh to fit at the bottom of the filter basket by cutting a stainless steel mesh. An aluminum mesh would have also worked, but I had a stainless steel mesh sitting around.

Then I added a paper filter on top. For these experiments, I used the same paper filter. This may have been a source of error, but I also did not see a particular issue with the paper filter to suggest the age was problematic.

The cut of the paper filter could also have been slightly better because I did observe donuting at the beginning of the shot.

I didn’t use thermal pre-infusion, and I used a simple flat flow of 1 ml/s at 90C. The input was 10g of coffee with a puck screen on top so that the headspace would be large since having the MeshPaper reduces the space in the basket.

Coffee Roasting

All coffee was roasted on the Roest using a BT/IT profile (Inlet Temperature (IT) controlled by Bean Temperature (BT)).

Metrics of Performance

I focused only on coffee extraction. Taste is king, but coffee extraction can still tell us something about efficiency.

Total Dissolved Solids (TDS) is measured using a refractometer, and this number combined with the output weight of the shot and the input weight of the coffee is used to determine the percentage of coffee extracted into the cup, called Extraction Yield (EY).

Data

All coffee had 1.9% water added to the coffee beans to reduce static. I pulled each shot into three cups to look at how extraction changed over time.

The general trend of darker roasts (lower Agtron) was the ability to extract higher.

The same was true with a MeshPaper addition.

However, when we looked at individual performance, the MeshPaper doesn’t appear to help.

It did seem to hurt EY, but that doesn’t say anything about taste.

These changes were very small, and I was not expecting these results.

This was also true for the lightest roast.

It is quite possible the design was flawed in the paper filter cut size or reusing the same paper filter. It could also be that this test coffee was not a good data point because all the coffee developments were the same test coffee. However, I am not seeing an obvious sign of improvement using this MeshPaper technique.

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