As the hour nears for us to use the new horizontal mechanical dryer at Beneficio El Manzano, we thought we’d post a few parts about the actual method of drying, how it functions, and specifically about the source of the heat that will dry the coffees.
Coffees at Beneficio El Manzano are dried by two primary methods; on the patios, and with mechanical dryers. Ever batch of coffee processed, will spend at least one full day on the patios, drying solely by the heat of the sun, however, once coffees reach a moisture content below 40%, they may be safely put within the mechanical dryers.
Dryers can handle loads of coffee parchment from 4,500 - 6,000 pounds. They are powered by electricity, but heated by fire, within furnaces connected to the main shaft of the mechanical dryer, which the coffees pass through, as they cycle throughout the dryer. This article is dedicated to the method in which those furnaces are heated, and sustained.
Connected to the mechanical dyers, is a room containing two dryer furnaces. These furnaces generate heat by burning coffee parchment, taken from the coffees when it goes through the hulling station.
The first step in the process is loading the furnace. Within the room, are multiple sacs, filled with coffee parchment. Each of these sacs is manually carried up the ladder, and poured into a hopper that will feed the furnace.
As the parchment is fed into the machine, it will be burned within the motion of falling, so that it is consumed by the flame before it lands at the bottom of the furnace. The amount of parchment fed into the machine, is determined by an automatic probe, or thermocouple, which, measuring the temperature of the furnace, determines whether to add or withhold parchment. The temperature of the furnaces are set between 125 and 135 degrees Fahrenheit, meaning that the temperature of the mechanical dryers will never fall below, or rise above, these presets.
If the temperature of the machine falls to 125 degrees, the thermocouple activates the machine to feed more parchment into the furnace, until the temperature is again stable, where it activates the machine to refrain from adding more parchment, so that they temperature does not rise about 135 degrees.
Furnaces are also, consistently monitored by a full time worker, who maintains the capacity of the parchment hoppers, while monitoring the temperature of the furnaces and the moisture content of the coffees within the dryers.