Roasting Machine Designs – The roaster is a customized oven that heats the coffee beans in a hot air stream while continually churning and mixing the seeds for the proper roasting machine.
In today’s specialty coffee market, various roasters are employed, including conventional drum roasters, indirectly heated drum roasters, fluid-bed roasters, recirculation roasters, and a few more.
Rec R collects a portion of the exhaust and sends it to the combustion cage to help roast heat production. I’ll refer to the non-circular roaster that circulates emissions as a “single-pass” roaster.
Each roaster design has its advantages and disadvantages. Still, no new configuration can deny the appeal of roasters with traditional drums, a plan that has remained nearly untouched for over a century.
The traditional drum roaster is made of steel or solid iron drums that We may rotate horizontally on a shaft with a flame below. The fire heats the drum, and the air pulls through it.
A fan pulls hot air from the combustion chamber through whirling particles, while smoke, steam, and many other byproducts of the roasting process escape via a vertical pipe, or “chimney,” and burn out the machine. Due to direct heat transfer in contact with the heated drum and convection from the air moving through the drum.
After the roast is finished, the operator opens the open door and puts the roasted seeds into the cooler, which is stirred while a powerful fan sucks room-temperature air through heaps of roasted seeds for fast chilling.
A double drum of two layers of concentric steel separated by a few millimeters is used in the most roaster traditional drum cage. Direct contact with the flame warms the exterior of the double drum while the interior stays cold.
Conduction heat transmission is reduced with double drums, reducing the possibility of flare-ups, scorching, and facing. (From here on out, these three are referred to as “burning particles on the surface” in this text.) If you’re going to purchase a traditional drum roaster, look for one with a double drum.
Pros: The roast gas stages provide a clean roasting environment, and the drum is an effective thermal transfer system that conducts electricity, particularly in the early minutes of a series.
Cons: Particles may readily burn on the surface of metal drums due to overheating.
That is a traditional drum roaster. Coffee beans (brown arrows) enter the roasting chamber (1) through the input head cellar (2). Hi Sauk, I’m roasting some seeds and putting them in the cooling bin (3).
The cyclone mechanism (6) traps the chaff while air (blue arrow) travels through the combustion chamber (4) via roasting drums and out through chimneys (5). (silk shell).
URG Probate: Some manufacturers employ double drums and replace them with a static plate or “heat shield” between the flames and the drums to save money. Despite manufacturer claims, single-layer drums with heat shields are often inferior to double-layer drums.
The issue is that since it remains motionless and is directly exposed to the flames, the heat shield gets incredibly hot (Double drum rotation should constantly avoid heating into a specific area).
In a regular roast, I used an infrared meter to measure the temperature of the heat shield at 510 degrees Celsius. When shutting off the fire, the heat shield impacts the operator’s control by spreading enormous volumes of heat.
Indirectly heated drum (IHD)
Hot gas from the combustion cage is sent through the drum by the machine using IHD. This construction shields the drum from direct fire, enabling the operator to utilize greater roasting temperatures without burning the particle surface.
The IHD roaster mixes the seeds in the drum for uniform roasting. It pushes them into the cooling bin individually for effective chilling after the roast, much like a traditional roaster.
Adv: Compared to most other systems, IHD offers a clean roasting environment and enables quicker roasting at high temperatures with less chance of burning the grain surface.
Disadvantage: This design uses less energy than a traditional roaster.
Hot airflows are used in fluid-bed roasters to keep the seeds aloft and rotate in the roasting cage. Because the particle loses its weight during roasting, maintaining appropriate particle rotation in these machines requires a high airflow at the start, which progressively lowers as the roasting process progresses.
Most fluid-bed roasters don’t have cooling bins; instead, room-temperature gas is blown through the roasting cage to cool the grain after the batch. The cage surface is heated, interfering with the cooling process. Therefore this solution isn’t ideal. Many folks who utilize this equipment get their cooling containers and use them.
ADV: Fluid-bed roasters are inexpensive and dependable, have tiny footprints, and do not burn beans on the surface.
DISADV: Excess airflow ruins the flavor and affects energy efficiency; the operator must strike a balance between gas installation and gas flow to get the most excellent taste, which necessitates proper particle rotation.
Heat is transferred mainly into the grain via convection in fluid-bed roasters.
The gas heated in the combustion box (1) passes through the roasting cage (2) and out the chimney, while the chaff is retained by the cyclone (3).
The seeds enter the roasting cage through the funnel, circulate on the bottom of the hot gas in the roasting cage, and escape by the cage door.
In contrast to the single-pass roaster described above, a recirculation roaster recovers part of the exhaust. It recirculates it through the combustion cage to preserve heat, lowering the roasting process’s fuel consumption.
This machine has become quite popular because of its excellent energy efficiency, bean-surface-burning restrictions, and ability to generate a highly steady, humid enough, and reproducible environment.
Stable surroundings improve automated roasting software’s ability to assess pre-programmed roast profiles on the surface. The increased possibility of smoky tastes owing to particles in the gas with smoke from the roasting process is a severe flaw.
ADV: A recirculation roaster saves fuel and roasts quickly while reducing the danger of B-s-b. If profile software is utilized, they demonstrate it automatically.
Roasters have reported smokey tastes developing on occasion.