Every coffee roaster knows the importance of approaching each lot with it’s own roasting profile. In some case with small adaptations, but sometimes choosing a completely different roast curve. Part of your roast profile decision is based on the density of a bean. High density indicates, that with a similar volumetric measurement you have more weight. Water is quite dense. A liter of water weighs almost 1 kilogram at room temperature. The denser a coffee bean, the harder for heat to penetrate through the outer wall towards the core of the bean.
In high altitude regions, coffee growers can even be found at altitudes above 2000 meters above sea level (e.g. Ethiopia). The coffee fruit will mature slowly and therefore produce quite dense beans. Did you know that coffee cherries start maturing first at the bottom of the mountain? Low altitude regions in countries such as Brazil might average only 1000 meters above sea level. Altitude has an important influence, but is definitely not the only factor. Processing method (naturals tend to be softer), but also variety, climate and other variables influence bean density.
Enough about the origins of density! This blog post is to provide insight into equipment to measure bean density. We setup a small test with the Sinar Beanpro 6070 and Lighttell MD-500, to achieve the following two things: Spectrum & Output.
Step 1: Choose your coffee. In this test we are using an Ethiopian lot (Small producers, Sidama gr. 2), Brazilian (Estate lot, Pulped Natural) and Colombian (Small producers, combined group lot).
Step 2: Add green coffee to each machine using the measuring cup, we get the data output Density (g/l), Humidity (%) and Temperature (Celcius).
Step 3: To improve the significance of the result, it is important to take 3 measurements per test. In this test we have averaged 3 tests from 3 different samples per coffee. All results are averages from 9 data points.
The Lighttell (our standard equipment in Amsterdam) consistently gives an output of 60g/l higher, and roundabout 0,6% humidity lower. However, between the three coffees the average difference between the coffees on the same device are relatively similar.
Spectrum of testing equipment:
Sinar: Low 700 - Medium 750 - High 800
Lighttell: Low 750 - Medium 800 - High 850
Each machine is calibrated to a different benchmark, only allowing you to compare results from the same piece of equipment. This issue is more commonly identified among humidity readers. These devices need to be robust and in case of heavy use, require yearly calibration using a certified sample from the manufacturer. In the case of density calibration is easier, the Lightell MD-500 can be calibrated withing 2 minutes using the accompanying weight.
So how can a roaster make use of density numbers? Ask for the SPECTRUM of the measurement device!
In The Coffee Quest Lab we are consistently using the same machine allowing us to confirm the range. Reading the numbers give us insight on how the coffee will roast, blend or grind, before the first roast. Make sure to know the spectrum before comparing density results from different importers.
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