Estimating TDS from Refractive Index

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

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

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

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