What is a coffee density check? And why do we do it?
Density, in a coffee bean, is the measurement of the amount of coffee that can fit into a 3-dimensional space.
It’s the mass, divided by the volume.
A density check on green coffee beans is done by using two different methods to figure out the density of the coffee. These are: Freely settled density and displaced density measurements. The results gathered from these tests are used to help us better judge the roasting process.
The density (hardness) of green coffee beans is an important factor when it comes to the roasting process. The density of coffee beans affects the duration and heat needed.
Each new batch of green beans that comes into us gets a density check.
The checks not only show the quality of coffee coming in. But also it tells our roasting team what heat and duration the beans should be roasted for.
Creating a perfect batch that is equal in flavour, aromas, and texture every time.
Coffee beans grown at higher altitudes tend to be a much denser bean than those grown at lower altitudes; each different type of bean will have its own range of density which we look for.
The method we use most and gives us the most accurate results is the water displacement.
The principle is that you measure out 50ml of water and 25g of green coffee beans.
Tip the beans into the water and then measure the amount of water that has been displaced by the beans.
We use measuring beakers to ensure we can accurately measure the amount of water that has been displaced.
You can then ascertain the volume of coffee beans by dividing the coffee beans original weight, so 25g, by the amount of water that has been displaced, 20ml and you get its true volume.
In this example, it would be 1.25 g/ml
When evaluating the density of our green coffee beans we’re looking for the coffee beans to sink in water, as they should be denser than water. This is because water has an equal mass to volume ratio of 1.0 g/ml. As a result, any beans that float are considered to be low-density beans and likely to affect the taste and quality of the roasted coffee.
By keeping records of the density of our coffee beans density we are able to observe any changes and make the required adjustments to our roasting times and temperature. Also, we are able to observe patterns throughout different seasons and producing countries giving us greater understanding about the different origins of coffee that we use.
It was Archimedes who discovered the displacement method, the physical law of buoyancy. He stated: Any object, wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object.
Thanks to Archimedes, we use displacement to help us brew the perfect mug.