Linked Temperature Roasting (LTR)

We have developed a unique roasting process that coordinates the temperature of the roasting air with the bean temperature. We refer to this as LINKED TEMPERATURE ROASTING orLTR. The theory behind the process is simple: When an object is cool, its surface can handle very high temperatures for a short period of time. This is because the temperature at the surface of the object is quickly conducted to the much cooler interior of the object. However, as the interior of the object absorbs more and more heat, the rate of heat transfer from the surface progressively decreases. As the object heats up, the surface becomes more and more vulnerable to the heat. A simple way to understand this concept is to think of what happens to your finger if you pass it very quickly through the flame of a candle. The first time you do it, you don't really feel the heat that much. But, if you continue to repeatedly pass your finger through the flame, it will begin to become more painful with each pass. If you were somehow able to reduce the temperature of the flame for each pass, you would be able to quickly warm up your finger with out burning the surface. Well, that's essentially how we roast our coffee beans. We use what's referred to as a "fully modulated" burner system. This means that the output of the burner can be controlled and set at any level. This is where our system differs from most of the highly sophisticated roasting systems in use today. We discovered, after a great deal of trial and error, that there is no direct relationship between the output of the burner and the resulting temperature of the air being delivered to the beans. Initially we had been attempting to decrease the temperature of the roasting air as the bean temperature increased during the roasting process using simple "single loop" controller. Nothing we tried would work, and we always had to take over control from the controller, and control the roasting air temperature manually. Trying to manually execute a precise roasting air temperature profile in conjunction to the bean temperature was no picnic, and for really sophisticated roasting formulas, it was impossible.

It became obvious that the computer would have to monitor the roasting air temperature and the bean temperature simultaneously, while adjusting the burner output to achieve the desired roasting air temperature for any given bean temperature. This required having a computer execute "roasting formulas" through a PLC that controls the burner system, enabling us to successfully link the air temperature to specific bean temperatures .

We have achieved a very high level of control over the process, and results that we previously thought were impossible.  Not only are we able to roast coffee in a with a process that is far less traumatic to the beans than traditional methods, but we are able to do so consistently.

The following is a description of our roasting stages.

The technical term for increasing, or decreasing temperature is called "ramping". Our roasting process consists of 7 distinct ramp stages.

1) Dehydration Ramp

During this stage, the air temperature is brought to a fairly high temperature, and then the beans are "dropped" into the roasting drum. The purpose of this stage is to flash the moisture off the surface of the beans, and to draw any excessive moisture out from the interior without boiling the water. Boiling water suddenly inside the bean would severely compromise the internal structure of the bean. While the successful roasting of coffee beans requires a certain level of moisture to be present, excessive moisture will degrade the process. Too little moisture will also have a negative impact on the chemical reactions during the roasting process. As soon as the beans have been "dropped" into the drum, the computer begins to ramp the temperature down. The degree of moisture will be the most significant factor affecting how quickly the temperature is ramped down.

2) Stabilization Ramp

The purpose of this stage is to allow all of the beans to become stable in relationship to one another. The air temperature is ramped gradually lower until the beans have reached a temperature of 230 F. This is the temperature at which sugars begin to melt, and is the beginning of the actual roasting process.

3) Momentum Setup Ramp

Once the beans have reached 230 F the air temperature is rapidly increased to its highest temperature. This stage is "setting up" the roaster environment for the most critical stage of the roasting process.

4) Momentum Ramp

This stage begins when the desired maximum air temperature has been achieved. At this point the beans are being subjected to the highest air temperature of the entire process. As the beans begin to increase in temperature, the computer ramps the air temperature down fairly quickly. What we're trying to achieve here is to get as much temperature into the beans as early in the process as possible. There is a metaphor, "thermal momentum", in the roasting business that is crucial for a person roasting coffee to grasp. If you don't get enough heat into the beans early, there is no way you can make up for it later on during the roasting process without considerably compromising the beans. From the standpoint of temperature, you have to get the beans "moving" early on.

5) First Crack Ramp

As the beans approach 350 F, they are approaching a phase in the process called "the first crack". What is actually happening is that the chemical activity inside the beans is producing a much greater amount of gases, which results in an extreme build up of pressure inside the beans. The pressure becomes great enough that some of the beans can't expand rapidly enough, and they split open making a very audible snapping, or cracking sound. The computer ramps the air temperature down in preparation for "the first crack". Driving the coffee beans too hard through the first crack will damage the interior of the beans, and ultimately result in the excessive loss of the desirable volatiles being produced by the roasting process.

6) Development Ramp

During this phase, the most crucial chemical activity occurs within the beans. The chemical reactions occurring are known as Maillard reactions, and are responsible for the flavor of coffee. It is during this stage that the flavor of the final product is developed, hence the term "development ramp". The following is a general list of compound categories, which make up the more than 800 compounds in roasted coffee, will give you an idea of the complexity:

  • Acids
  • Esters
  • Nitrogen Compounds
  • Pyridines
  • alcohols
  • Furans
  • Oxazoles
  • Pyrroles
  • aldehydes
  • Hydrocarbons
  • Phenols
  • Sulfur Compounds
  • amines
  • Ketones
  • Pyrans
  • Thiazoles
  • Anhydrides
  • Lactones
  • Pyrazines
  • Thiophenes

The beans must be given enough time to "develop", that is to allow all of the chemical reactions to occur. Driving the beans too rapidly through this stage will result in coffee that is less than it can be. However, if the beans spend too much time in the roaster during this phase, the result is what is known as the beans being "baked" resulting in a considerable loss of flavor. The beans are smoking quite noticeably at this point, and too much time means too much loss. What's important to understand is that if beans were not heated up enough earlier during the roast, an excessive amount of heat would be required to avoid keeping the beans in the roaster too long. Even worse, applying excessive temperatures to the surface of hot coffee beans will affect them adversely.

7) Finish Ramp

Once the beans have "developed" most of their full flavor, the air temperature is quickly ramped down to allow the beans to "finish". There is a certain amount of physical transformation in the beans that must occur at the end of the roast. The air temperature in our roaster is as much as 500º F lower than in standard roasters. The reason we are able to do this stems back to the Momentum Ramp. Using more heat in the beginning enables us to use less at the end. We have been able to eliminate "roasting defects" that were previously impossible to avoid in certain roasting situations. Theory is one thing, but this method of roasting actually produces noticeable results.

Each coffee we roast has its own roasting formula. One the greatest advantages to our process is consistency. Split second timing and consistent roasting air temperature profiles are executed every time. While using state-of-the-art technology takes much of the romance out of coffee roasting, it's the only way if you want the best results. There are limitations to what a human can do, and computer technology takes us well beyond those limitations