The term, "Roast Degree" pertains to how far along in the roasting process, a batch of roasted coffee beans are.

The term, "Roast Degree" pertains to how far along in the roasting process, a batch of roasted coffee beans are.

Although there are a number of physical and chemical changes that occur during the roasting process, the easiest and most practical way to gauge how far along in the roasting process they are, is by measuring the color of the roasted beans.

Color has traditionally been measured by batch sampling. This is because at the time the current standards were developed, the technology to measure color continuously, while roasting, was simply not available.

In fact, to obtain any kind of repeatability with some of the more popular technologies available, the sample has to be ground, and carefully prepared, so that the surface is as flat as possible, in order to eliminate reflection errors caused by peaks and valleys.

Sample preparation requirements employed today with some of the more widely used technologies, like this Agtron Spectrophotometer, include separating out specific grinds by size through sieving, to further help with the problem. Afterwards, the sample is flattened by using a strike stick, in a defined methodical process, and then turned by hand, to help increase the area of the sample being scanned. The larger the sample being tested, the more likely it will

be representative of the batch.

Even with careful training, human error is unfortunately a reality. In addition, the technical limitations of some of the more popular instrumentation, cause problems with repeatability, especially with extreme light or dark samples.

While it is no longer completely necessary to sample batches during process roasting, it is practical to use this discipline when sample roasting. Here, small (100 gram) batches are roasted to create roast profiles, where different time, temperature, and color parameters, are applied to various green coffee bean samples.

It has been well documented that higher temperature, and shorter term roasts, will yield roasted beans with larger bean size, as well as an increase in the number and size of pores. This is important, because more and larger pores, allow for accelerated oil and moisture migration, which affects not only taste, but storage time and method considerations.

So it is not only possible, but more so a reality, that the same sample can be roasted to the same color specifications, but produce roasted coffee with different physical and chemical characteristics, by altering the temperature and time parameters. Therefore, in order to repeat a roast profile in processing, the time and temperature used to reach a specifed color, are all variables that need to be logically accounted for. Most roast profile software allows for programming the green beans physical charcateristics in, because obviously more wet or dry beans, even from the same batch, will require slightly different roasting conditions to reach the same point.

While it is in theory possible to detect reflection differences between

beans with the same color, but slightly different physical properties, (perhaps by the amount of reflection difference caused by oil migration) it is more practical and useful (The migration of oils to the surface is an ongoing process, and would require specific time constraints that may prove difficult to employ) to categorize profiles by the time and temperature parameters used to reach the target color.

The ColorTrack Benchtop System (pictured above), is actually a modified, inline, continuous reflection measurement, analyzer. The nature of it's technology fixes a lot of the problems normally associated with measuring color in roasted coffee beans.

The ColorTrack utilizes a rapid fire laser module, that operates specifically in the 785 nanometer range of the color spectrum, which is the optimal range for sensing shade differences.

It is relatively impervious to ambient light, as well as much less sensitive to distance, thereby eliminating most if not all of the sample preparation and human error problems associated with roasted coffee color analysis.

The sample is rotated automatically on a turn table, so that the

entire path of the laser transmission is measured. The results

are then collected by a data acquisition module, and converted to a digital signal, which is then expressed in a statistical format with graphic representation.

Assuming there is a direct correlation between the average color of the exterior of the roasted bean, and the ground sample, it may in time become unneccessary to sample in batches. In fact, FreshRoast Systems Ventless Roasters, currently employ real time color technology succesfully in it's roasting process.