One of the most popular pages on our website discusses how to measure green coffee bean density. It tips its cap to high school chemistry class, calling for scales and beakers and graduated cylinders, although the process is actually quite easy. It does, however, beg the question: does green coffee bean density really matter?
And that is the main point we want to convey in this very brief Take2 overview: green bean density matters in how you roast a particular coffee. This topic could consume pages, so we're limiting it to three high-level points: the meaning of bean density, roasting denser coffee, and roasting less dense coffee.
First, it's important to know that denser coffees are often referred to as “hard beans” and less dense coffees “soft beans.” It’s helpful to picture the beans this way. You can often even detect this in the sound of green coffee as you pour it into your roaster – hard beans “ping” and soft beans “thud.” Or you can detect it by looking at the center cut in the middle of the green bean – hard beans having a tight center cut and soft beans a more open one.
Density Down Low.
Density essentially refers to the concentration of cells and compounds within a coffee bean; the amount of stuff jammed inside. Therefore, dense coffee beans have greater mass and more complex structure. Much of this is due to the fact that denser coffee typically grows at higher elevations. The cooler climates typical of higher altitudes cause beans to mature more slowly, providing more time for complex concentration to develop (including favorable features like acidity). In a very general but helpful sense, coffee grown at higher altitudes is typically “better” tasting coffee.
Roasting Tips for Hard Beans
Denser beans are going to conduct heat more efficiently and will usually roast a little faster than less dense beans. You want to gradually draw out the internal moisture of any coffee you’re roasting and since denser beans conduct heat more efficiently and uniformly, they can handle high energy (heat) during the first part of roasting. Once the beans are fully heated you can gradually scale the energy down throughout the roast cycle. (If you’re roasting with a Fresh Roast unit, check our tips and suggestions here).
Roasting Tips for Soft Beans
If you looked at a coffee bean under a microscope you would find the soft beans are far more porous. These air pockets are like little insulation bubbles that slow down the transfer of heat from the surface of the coffee (your roasting chamber) to the core of the bean. If you run things too hot, you can easily scorch or “tip” (burn the tips of) the coffee beans. This porosity makes the beans less uniform and requires a more gentle heat application to develop evenly, especially early in the roast cycle/drying phase. This is often evident in natural / dry process beans that tend to celebrate the “natural” differences in every bean.
The best way to learn how density affects your roasting is to know the density you’re working with and carefully measure data (time to first crack, development time, etc.) throughout your roast cycle along with cup results. If you don’t want to take the time to measure the actual density of each coffee, note the elevation the coffee was grown and over time you’ll gain an understanding of how elevation (a partial indicator of density) guides your roast plan.