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Measuring coffee extraction - my methodology

October 17, 2021

Over the past few months, I've dedicated a lot of time to learning more about coffee extraction and how to build the right toolkit to measure as accurately as possible in a home setting. I made a few simple changes that should help improve accuracy and the trustworthiness of the numbers I share.

My approach for Orea has definitely not been one that's in the chase of numbers. But I do believe in understanding what's happening "under the hood" and being able to communicate that to people. The goal is to help others understand what they're getting from their brewer and also to help them understand what they like and why they like it. It's also a helpful marker for what changes between versions or prototypes when all other aspects are held constant. It helps me benchmark against competing products too. While this kit and these improvements are surely going to increase accuracy, I'm aware that this is still not a research lab with 100% perfect conditions, but this is an acceptable level for now (for me).

The kit is quite simple:

  1. 1 x PAL-Coffee(BX/TDS) Digital Hand-held “Pocket” Refractometer
  2. A set of test-tube bottles with cork caps
  3. A dedicated bottle of distilled water
  4. A glass stir stick

To measure coffee extraction, we need three simple variables. One of them is the weight of coffee you brewed with. The second is the total volume of coffee you brewed. The final piece is the TDS value, which measures the total dissolved solids in the brew liquid. To get all of this, I use the following steps:

  1. I record the actual weight of ground coffee I use to brew
  2. Right after I'm done brewing, I weigh the total brewed liquid (coffee grounds always retain some liquid, so if you brew with 300ml of water, you will actually only have 260-270ml of brewed coffee)
  3. I grab a representative sample of the coffee as soon as I've weighed the liquid (in order for it to be representative, the liquid should be well-mixed and to achieve that, I stir with a glass stick right before taking the sample)
  4. I immediately place the lid tightly on the test-tube bottle once it has the sample in it as to avoid any evaporation
  5. I allow the sample to cool down to room temperature, 15-20 minutes
  6. I zero and calibrate the refractometer with distilled water right before measuring the sample and then clean it dry with a lint-free cloth
  7. I shake the sample test tube so I can make sure the bit I measure is as representative as possible
  8. I take a few readings and record the measure that stabilises - this gives the TDS value we need to calculate extraction
  9. I calculate the extraction with a simple formula, but I made a calculator to make it easier

The improvements I've made have been around collecting representative samples and making sure to prevent evaporation in the process. Adding the stir stick and making sure the coffee is well-mixed before collecting the sample has been very helpful. The test tubes with lids have been an important addition too, because they really help bring the sample to room temperature while preventing evaporation - so the results should be a lot more reliable. Making sure the liquid is well-mixed at all stages has been an important change in my process too. Finally, having the 1L dedicated distilled water bottle helps keep things easy. I can clean the test tubes and zero in the refractometer without any worries.

Hopefully all of these changes will help me provide accurate measurements for different recipes, different techniques, and different versions of Orea. If you are one of the folks that have more experience with the topic and you see something I can improve in this process, please let me know. I'd really appreciate your feedback and thoughts! 

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Measuring coffee extraction - my methodology

I recently made some important changes in my kit and my approach to measuring coffee extraction in an effort to publish more accurate data. This post explains my approach and what changes I made.