The average real densities for the vacuum belt dried coffee samples are compared with a spray dried
and a freeze dried instant coffee sample. Additionally the averaged real density value for the coffee
samples in finely ground form is represented. These samples have been produced from the original
samples by grinding within a ball mill. Milling time of 2 min has been determined by a primary
experiment analyzing the time needed, from which on a further milling does not lead to any differences in
the particle density. Within this investigation it could be shown, that the process parameters of the
vacuum belt drying process have only a minor influence on the particle density, which can be directly
concluded from the deviations in all measurements preformed with all vacuum belt dried samples
represented in figure 3 (left). It can further be seen that the vacuum belt dried sample have the highest real
density of the particles, even higher than the freeze dried sample. The comparison of the three samples to
the uniform powder value leads to information about the porosities of the particles. The difference
between particle and powder value corresponds to a gas volume included and non-accessible within the
solid. This value is very important for the product quality, as it influences the dissolution properties of the
product. Additionally if the real density is lower than the density of water, the product will float and
therefore will not dissolve easily in water.