Coffee Data Science
Dirty Pipettes and Refractometers Coffee
How clean is clean?
Typically, the cleaner the measurement tools, the better, but how much better? In coffee, the key measurement outside of taste is Total Dissolved Solids (TDS), and there are a few ways to get the desired sample. Usually, one uses a pipette, but to use an unused pipette for each sample can be wasteful. Is it necessary?
Let’s get dirty and find out!
I have a habit of using a pipette until I clean it or it breaks because I don’t want to be wasteful. Over time, some residue builds up, but for the purposes of my experiments, the variable slowly changes. For larger tests in the same day, I will use a new pipette especially sugar tests.
I have 3 pipettes: clean, used, and dirty (so dirty, I should throw away). I then used a sugar solution as a more constant sample, collecting 10 samples using each pipette.
The clean and used pipette were pretty close, but there was an impact for the dirty one. The variance wasn’t wild though.
Calibration
I calibrated with distilled water, and the filtered water sample read 0.00%, but before calibration, the samples read around 0.32%.
When I repeated the test, the samples after calibration were offset by that amount.
This test shows at espresso strength, the difference between used and clean pipette is interesting. It is possible at filter strength that pipette cleanliness could have more of an impact. I was concerned that a dirty pipette would have had a much larger impact. In the worst case of a dirty pipette, it is 0.10% offset. On the other hand, as long as I use the same pipette, the error may not be apparent amongst other noise.
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