Category: Uncategorized

In my previous post, we looked at the effect of grinding on coffee density. When we plotted void ratio vs. burr spacing for tamped espresso pucks, we noted that void ratio drops at fine grind settings, and I speculated that this might be due to fines production. In this post I’d like to develop a… Continue reading A Model of Fines Production

In a previous post, we looked at the design of my homemade gas pycnometer. For the past several months, I’ve been measuring the weight and volume of the whole and ground beans for my morning coffee. In this post, I’d like to look at some of those measurements, and then we’ll dig a little deeper… Continue reading Density of Whole Bean and Ground Coffee

Three years ago I built a simple “oedometer” to measure how coffee compresses under pressure, and I immediately started thinking about how to build a device that could log displacement vs. applied force while tamping an espresso puck. The project got a big boost when a friend on Home-Barista offered to send me a small… Continue reading A Logging Tamper

Three years ago I built my first gas pycnometer to measure the volume of coffee beans using changes in air pressure. Since then, I’ve built many more of these, each trying to solve some issue I discovered in the previous design. These improvements include: Rather than walk through each iteration of the design, I think… Continue reading A Better Gas Pycnometer

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

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

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

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

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 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