Useful Information - RO-BO Mechanical Workshop

EFFECTS OF THE MILLING

The desired effect during the grinding process is the fragmentation of grains. Its effectiveness is evaluated empirically by rubbing the powder between the fingers, but it would be more appropriate to apply the most suitable analytical techniques. In grinders is common to measure temperatures around 80 ° C, which probably correspond to temperatures in the order of 100 ° C.  Despite temperatures well away from those of roasting, they can still activate Maillard reactions that worsen the organoleptic qualities of the coffee. High temperatures during the crushing of the grains facilitate the release of volatile aromatic substance, the cells that do not crumble (approximately diameters exceed 50 microns) maintain their internal gases that contribute to the formation of foam in the cup. The breaking of the grains also facilitates the transpiration of the oils to the surface of the powder. The fat content is very viscous at room temperature (70 mPa s), but already at 40 ° C begin to be fluids (25 mPa s). At temperatures typical of the milling, slide easily between the cracks and cover the particles, then return to the state semi-solid viscous. Are modified so the cohesive properties of the powder, which will have repercussions in the phase of percolation, increasing the hydraulic resistance.


VARIABLES OF THE MILLING

First of all is necessary to consider the variability of the mixture. The coffee that you normally use, never comes from a single cultivation, but each coffee roasting use beans from more countries and more variety to build its own characteristic blend. Then the grinding has to do with grains of different composition and hardness, features that can vary over time, being the coffee a product of agriculture that depends on the laws of the climate and collection method.The degree of roasting and the consequent amount of trapped gases can affect the stability of grinding, so the coffee is often degassed at rest in silos. Water-cooled beans have very different characteristics from those air-cooled: the latter have a lower moisture content, while the former are more tenacious, and this implies that it is necessary to apply more energy to break them, then you are likely to reach higher temperatures during the process . Moreover, during the water cooling, for the high temperature swing the cell walls are contracted rapidly, breaking and releasing part of the trapped gas. Regarding the grinder, the distance between the millstones adjusts the size of the powders. Is necessary that the mechanics is very precise and must not show hysteresis. There are then typical parameters of each machine, linked to the feeding mechanism and the possible pre-shredding. Acting on the speed of grinding is an expensive method to accomplish, but it seems to be a fairly efficient. Other disorders entrants in the process can be of various nature and not easily interpretable. The friction during the crushing creates dissipation of mechanical energy and heat build-up that causes a differential expansion of the rotating parts. In industrial practice it is common to recycle or reject the ground obtained before the machine has reached thermal stability. For this RW-70 allows you to start the process only when it has reached the right temperature to work, so that there are no differences between the ground product at the beginning and end processing.
Maintain the coffee at a constant temperature of 33/35 ° during the entire grinding process seems, therefore, the most suitable solution to achieve the best possible quality of the final product.
The wear certainly affect the qualitative yield: not properly sharpened blades increase the ratio compression/cutting, creating hot spots that give a bad flavor to the coffee.
Problem solved by our grinders that, thanks to special alloy studied for their merger, the sequential development of the blades and their profile, maintain almost unchanged their performance up to the time of replacement (Described and illustrated in the instruction booklet).