Coffee Beans & Ground Coffee

A roasting plant conveys the same product twice in two completely different states, and most handling problems come from treating them alike.

Beans break, and broken beans cost twice

Roasted beans are porous and brittle, and the damage is done by velocity rather than by the machine type.

In a dilute phase line at 25 metres per second, beans arrive chipped and accompanied by fines that were saleable product a moment earlier.

Dense phase conveying at low velocity, gentle bends with generous radius and soft let-down into silos keep the bean population intact.

• Check the fines fraction before and after the conveying line, not only at the end of the process.
• Avoid sharp deflector plates in bends, which concentrate impact at one point.
• Limit free fall into silos, where the first beans hit steel and later beans hit each other.

Degassing is a process condition, not a nuisance

Roasted coffee releases carbon dioxide for days, and the gas has to go somewhere.

In a closed silo the gas accumulates and can displace oxygen, which makes confined space entry a serious hazard, and in packaging it causes bag swelling if the product is sealed too early.

Degassing time, silo venting and the sequencing between grinding and packing belong in the plant design rather than in operating practice alone.

Ground coffee behaves like a fat-bearing powder

Grinding exposes coffee oil, and oil makes the powder cohesive, sticky on walls and prone to bridging in small hoppers.

Fine grinds for espresso are markedly more cohesive than filter grinds, so one hopper geometry rarely suits the whole product range.

Keep the residence time in ground form short, because the same oil that causes sticking also oxidizes.

Dust, fines and explosion risk

Coffee dust from grinders, silos and dust collectors is combustible, and roasting plants also deal with hot material and chaff.

Smouldering chaff from the roaster is a documented ignition route into downstream equipment, which makes separation, spark detection and collector protection worth reviewing together.

What to establish before buying equipment

• Acceptable fines percentage after conveying, measured by sieve and agreed with the supplier.
• Bulk density for whole bean and each grind, which differ by a factor of roughly two.
• Degassing rate and the venting route for every closed vessel.
• Explosion characteristics of the grinder and collector dust, not of the bean.