KEEPING A HIGH PROFILE

Create Consistent, Reliable Roasts

COFFEE ROASTING, no matter what the technology, has always been a very special affair. Cowboys in the Wild West roasted coffees in a tin saucepan on an open fire and then ground the coffee with the butts of their guns. Thank goodness, technology has changed since then. Today, millions of pounds of coffee are roasted consistently to exacting cup characteristics, without even a shade of color variation or taste fluctuation. One of the ways this is done is through profile roasting, a technology that allows accurate control over a product as temperamental as coffee.

     The goal of profile roasting is to reliably and consistently replicate distinct and unique roast profiles. A roast profile is a graphical curve produced by plotting the temperature changes over time during a roast. Roast profiles differ, depending on variables such as green bean origin and desired roast level. In order to achieve this goal of consistency, profile roast control systems must give the roaster the ability to control the roast profile. The roaster should be able to control every step of the roasting process to achieve the desired bean temperature versus time relationship during a given roast.
     Profile roasting goes far beyond mere data acquisition, as I will make clear later on. A profile roasting system makes precise mechanical adjustments to the roaster throughout the roasting cycle, according to the user’s specification. Profile roasting control systems, indeed, are some of the most sophisticated tools available to roasters who want to reliably and consistently roast their coffees.

Once you’ve sampled, approved and purchased the quality coffee of your choice, one of the most crucial steps in the process is still ahead: to transform this promising green coffee into a delectable aromatic roasted wonder that will have customers singing your praises with orders in hand.
     All right, I am not a poet, but a technologist. However, I want to make a point about the aesthetic complexity of coffee. Coffee of even a single origin will yield many different experiences depending on how the coffee was roasted. Not only are there many coffee types, there are also many roasting methods. Profile roasting allows you to manage this complexity while cultivating the distinct cup characteristics of your coffees.
     Fifteen years ago, Bob Stiller, chief executive officer for Green Mountain Coffee Roasters was one of the first individuals in the coffee industry to switch his roasters to a profile roasting control system. As Stiller pointed out in Forbes magazine, “Some say there is an art to great coffee. I don’t care how artistic you are; there are too many factors in play. You need the technology.”
     Stiller turned out to be right, and the rest, as they say, is history. In the hands of a good roaster, excellent controls can bridge the gap between good green coffees and great roasts. But in the hands of an entrepreneur, excellent controls can also translate into a successful business strategy. The savvy customer of today demands not only a great cup, but also a consistent cup. In addition, the educated palates of these customers are very specific in their taste preferences. Profile roasting allows you to control the complexities of roasting consistently in order to meet customer expectations.
     Color, flavor and aroma—the very essences of coffee—are produced by chemical and physical reactions that take place during the roasting process. Along with green bean quality and blend composition, the physical and chemical changes taking place during these reactions determine the flavor and brewing characteristics of roasted beans. The job of any control system is to give the roaster the ability to manipulate these factors to produce his desired taste characteristics.

     For many years, roasting was always a hands-on job, requiring the experience and the unwavering attention of a dedicated roastmaster. Manual roasting requires careful scrutiny of every batch, where you use a thermometer, a stopwatch, and the cultivated experience of your senses to manipulate the roast process.
     In recent years, roasters have been able to use new technologies as a tool to support efforts to improve quality and consistency between batches. Simple automated controls introduced roasters to set point roasting, such as three-stage or multi-stage roasting, which offers some limited control over temperature set points. Most recently, technological development has focused on profile roast control, which is precise and flexible enough to cooperate with the roaster and powerful enough to replicate his desired roast profile consistently.
     It is important to understand the distinction between set-point (stage) roasting and profile roasting. Many automated stage roasting systems attempt to control roast profiles by adjusting burner output at a number of different temperature set points throughout the roast. Each individual set point becomes active after a selected roasting time has elapsed or after a selected bean temperature has been reached or exceeded. While this roasting method offers the roaster some control over flavor development during the roast, it is still subject to (sometimes large-scale) variations. A number of set bean temperatures by no means guarantees consistent cup characteristics.
     We cannot understand the distinction between set-point roasting and profile roasting without a brief foray into coffee chemistry. The chemical reactions involved in roasting are simply too complex to be properly managed by stage roasting. During roasting, both parallel and series sets of reactions occur, and affect one another. Bean temperature, as well as the concentration of reactants produced by earlier reactions, affects the rate and course of subsequent reactions. The earlier bean temperature history determines which reactions dominate and the balance of products at any given time. The bean temperature development over the entire course of the roast will favor very different final flavor characteristics. Figure 1 provides an example of actual experimental data showing that even slight variations in temperature and time during roasting can affect the flavor and aroma of the roasted coffee.
     A few years ago, I demonstrated the practical implications of coffee chemistry for roast control systems at an SCAA trade show by conducting the following experiment: I roasted four batches of single-origin coffee from the same lot to the same Agtron color and the same end temperature, using three temperature set points and the same total roast time. Each batch exhibited significantly different flavor and aroma characteristics because of changes to the roast profile curve between the set points.
     A limited number of set points during which to manipulate a roast profile allows for only limited control over bean temperature development over time. Furthermore, there is another drawback to simple automation controls, which rely to a large extent on manipulating burner output to control the roast process. “Roaster burner adjustment alone provides an imperfect means of achieving bean temperature profile control,” says Professor Henry Schwartzberg, retired professor of food science and engineering at the University of Massachusetts. “Coffee beans cannot withstand high burner temperature without burning or tipping. Using burner output alone to control the roast is also inefficient, because of the significant lag period necessary for the changes to take effect in the roaster environment.”
     In short, it is difficult to exactly replicate roast profiles through manipulation of the roaster burner temperature alone, because the adjustments take a relatively long time until they are “felt” and the varying changes in environmental temperatures lead to variations in the flavor profile for the bean. Automated profile roasting overcomes the limitations of automated set-point roasting.
     Profile control requires timely environmental adjustments. I believe that changing the rate of airflow into the roaster, for example, can provide a more efficient way of effectively manipulating bean temperatures without changing the flavor characteristics of the bean. Different environmental temperatures generate different flavor profiles for the bean.
     Therefore, a profile roasting system is a profile system only if it allows the roaster to manipulate the development of the coffee flavor/development continuously, at every stage of the roasting process. This detail of control allows roasters to reliably duplicate a distinct roast profile over and over again. The roaster can control the entire temperature path of the bean (rising quickly and then tapering off, or increasing slowly and then rising more quickly later on in the course of the roast), not just final roast temperature. In this way, the roaster can manipulate the curve so precisely as to specify a small 20-second portion of the roast where he wants to have a sudden surge in the rate of temperature increase. A true profile roasting system works with the calculus of the slope of the curve, rather than the linear arithmetic of a few set points.

Profile Roasting: Standards

     Profile roasting control complements and enhances roaster expertise and avoids impeding it. In all practical respects. Terminology and definitions have proven confusing, as is often the case. There is much confusion between data logging and control. A data logging system is capable of generating roast profiles, but is not a profile roasting system. Date logging systems only passively acquire data, while the profile roast control systems actively replicate the profiles through application to a controlled roast.

Some profile roasting systems include the following features:

1. Dual Control

Some profile roast systems adjust airflow, some control burner output, while others allow you to control both airflow adjustment (for bean temperature control) and burner output adjustment (for burner temperature control) in concert. Increased burner output tends to mitigate airflow, while on the other hand, increased airflow tends to deplete burner flame energy. Often the type of control you need depends on the roasting platform.

2. Proportional Integral Derivative (PID) Controller

A single loop profile system modulates the burner flame in order to manipulate the bean temperature curve. In order to avert bean-charring upswings of heat energy into the roasting chamber, a second independent PID loop can be added to control air flow and burner energy output. The goal here is to control total energy through either single or multiple PID loops.
     With this modified config-uration, burner temperature can now be constrained to levels that will not cause charring or tipping to the beans. And when the bean temperature PID loop demands an increase in fan speed to affect increased airflow, the burner temperature PID loop will impel more heat energy to counteract the additional heat employment imposed by that increased airflow. Conversely, the amount of burner flame will decrease at times of decreased airflow to counteract the additional burner heat pooling caused by the decreased airflow.
     The summary of this technical description is as follows: single loop PID controllers generally control through manipulating gas flow to the burners while holding airflow constant; multiple PIDs generally control both airflow and gas flow to the burners. The goal of both systems is to facilitate a controlled ascent of bean temperature along a desired profile curve. The desirability of any sophisticated PID control system depends upon many factors including, but not necessarily limited to: roasting platform, roasting style, cost, and the needs of your business.

3. Other Features
Some profile roast systems automatically adjust for changes in green coffee moisture content, barometric pressure, and humidity or other weather changes. This is beneficial because uncontrolled variables such as bean size and moisture content, ambient temperature, initial bean temperature and, to a lesser extent, ambient pressure all affect bean heating, and if not controlled, will result in flavor variations in the final cup.
     Another crucial feature is detailed historical data-logging capabilities, which are essential for analysis. Although data logging is part of a profile roast system, it is not considered a profile system per se because a data logging system only logs data and does not control the roaster. Ideally, the historical data logging capabilities will also include graphing and hard copy printing options.
     Some profile roasting systems allow you to roast manually, recording your actions so that the system can duplicate it automatically; this is called a learn-mode function. In the learn-mode function, a profile system will record all the process data that occur during the roast, and at completion of the roast will automatically generate a profile for that roast which can be used to reproduce those roasting conditions for subsequent roasts. Cupping notes can be added to each of the different history data files, and the roaster can develop a profile that consistently brings out the desired taste.

Remember that roast profiles which provide optimal flavor development can be determined by cupping roasted coffees produced using different candidate profiles. “Automated profile roasting aids the roastmaster’s expertise with a system to help control these variables in order to achieve consistent results from roast to roast,” says Lindsey Bolger, coffee manager at Green Mountain Coffee Roasters. “Depending on how the roastmaster integrates his or her skills with informed inputs to automated controls, the outcome at the cupping table can be consistently great, good, or repeatedly mediocre. The right system can link together the cupping table to a profile management system, with a roastmaster in between to manage the relationship between craft and science—what a great formula for exceptional coffee.”
     I have to agree. By combining specialty green beans, a good roaster and a great profile roasting system, roasters can create the perfect formula for consistent, quality coffee in every cup.

JOACHIM EICHNER is chief engineer at Praxis International, a leader in control technology
for the coffee roasting and emissions control industry. Since the age of 17,
he has been developing and perfecting roast control technology.
He can be reached at joachim@roasting.biz.

PROFILING DEFINITIONS

Profile Roasting Control System A roasting control system utilizing electronic process control hardware to manipulate the burner, airflow and/or drum rotation speed. There are variations in the types of process logic that can be used to perform these functions: Set point (on/off), ramp and soak (stage/linear) or non-linear (utilizes higher level math functions). All systems can use either an environment probe or a bean probe to control processes.

Set Point (on/off) Process Systems Set point control systems work with simple on/off logic, similar to the way a thermostat works. If the control temperature is below the temperature value set on the control system, the control system will turn the burner on. When the actual temperature reaches the set temperature value, the control system will turn the burner off.

Stage (ramp and soak/linear) Process Systems This type of system will follow a predefined path or program. The path or program can/will comprise of various sections (stages) that either increase in temperature value for a defined time or hold a temperature value over a defined time, hence the stage or ramp and soak designation. The ramp section is defined by increasing/decreasing the temperature value over a given time, the logic then breaks up the temperature into time increments which would look like a straight line between the two temperatures over the defined time, creating a linear line. The more steps, the finer the control over the roast process.

Profile Roasting Control Systems (non-linear process systems) In most cases all non-linear control systems are proprietary systems. The math function used to define the path can vary from system to system depending on the manufacturer but is generally more sophisticated than linear processors. The system may use various input information in determining profile path. There are many different designs of these types of systems. These systems are more complex than stage/ramp and soak systems.

Profile An analysis of the temperature path of coffee during the roast process, usually takes the form of a time and temperature graph.

Profiling The act of profile roasting and/or the act of making a hard copy profile of a roast temperature path, usually in a graphical form.

Profile Roasting (v) Taking some kind of measurable and repeatable action during the roast process to affect a change in the taste of the coffee by changing the roast profile.

Profile Roasting (n) The science of controlling the rate of heat transfer into the coffee during the roasting process, with the goal of optimizing flavor. Repeatability must also be a goal.

Data Logging The act of compiling time and temperature roast data in order to assist an operator in profile roasting. May be manual or automated.

Automation The automatic operation or control of any equipment, process or system.