We often use refractometers to measure total dissolved solids (TDS) of coffee, but these instruments don’t measure TDS directly. Instead, they measure the refractive index of the liquid—a characteristic related to the speed of light in the liquid—and then estimate TDS using an empirical relationship between refractive index and TDS. This relationship between refractive index… Continue reading Estimating TDS from Refractive Index

## Validating the DiFluid R2 Extract

Introduction A little while back, DiFluid sent me a pre-production version of their R2 Extract refractometer. Since then, these units have gone to production, and DiFluid kindly sent me one of the production units as well. One of the things I like most about the R2 Extract is that it displays temperature and refractive index… Continue reading Validating the DiFluid R2 Extract

## Calibrating a Cheap Refractometer

Introduction Recently, I’ve been comparing data from Salamibot with previous data collected using split shots. There are some systematic differences between the two data sets, so I’ve been looking closely at the two measurement procedures to identify the source of these differences. One potential source of error is the conversion from Brix measurements, given by… Continue reading Calibrating a Cheap Refractometer

## Introducing Salamibot

Recently, I’ve been splitting my morning coffee at various brew ratios, measuring total dissolved solids (TDS) in the first part, and using this information to explore extraction dynamics using various equipment configurations. This method has a few limitations: Splitting a couple of coffees each morning, it takes a week or so to gather data for… Continue reading Introducing Salamibot

## An Analytic Solution for Extraction

In a previous post, we looked at a numerical solution to a model of expresso extraction described by Moroney et al. in their 2019 paper. In this post, I’ll to look at an analytic solution for a simplified version of that model. You may be asking why we would want an analytic solution. Or you… Continue reading An Analytic Solution for Extraction

## A Simple Model of Extraction

A little while ago, Jonathan Gagné suggested that I should take a look at the plot of extraction yield (EY) vs. brew ratio. His hypothesis was that we could fit a particular curve to the data in this plot which would give some insight into the extraction process. The model When we think in very… Continue reading A Simple Model of Extraction

## Improved Puck Density Measurement

A couple of weeks ago, I spent a day grinding 115 doses of donation coffee from Level Ground, measuring the density of the tamped puck using a caliper, then measuring true density using a gas pycnometer. I’ve uploaded the raw results for this experiment to GitHub. I did a similar experiment previously, but identified several… Continue reading Improved Puck Density Measurement

## Measuring Density with Gas Pycnometry

In my very first post, I mentioned several ways of measuring density. Since then, I’ve talked quite a bit about measuring the density of a tamped puck, but there are a few reasons I’d like to be able to measure the “true density”, i.e., the density of the beans themselves: This is something we could… Continue reading Measuring Density with Gas Pycnometry

## Challenges with Density Measurement

The other day, I spent a few hours grinding coffee. In a previous post, I proposed a model of coffee grinding, along with some data from my morning coffee which seemed to support the model. However, it should be said that this isn’t very high quality data—there are very few data points outside the range… Continue reading Challenges with Density Measurement

## A Closer Look at Tamping

For some time, I’ve assumed that the specific force you tamp with has little effect, as long as you tamp hard enough that the puck stops compressing. However, the results of a recent experiment led me to believe this might not be the case. To check this, I purchased a Normcore spring loaded tamper, then… Continue reading A Closer Look at Tamping