For Master Roasters who want
Simple Sample Roasting and Peak Profile Production

 A large and enjoyable argument has gone on for some time about the two basic technologies of roasting equipment: there are drum-style machines that are said to achieve masterful roasts by browning coffee beans in a maturing atmosphere of enriched aromas. And, there is hot air technology that suspends beans in a clean but very hot airflow creating convection conditions to uniformly roast to peak time and temperature.

The argument is not settled here. But something else is offered that can enhance the outcome for any roast master on any equipment, whether drum or hot air. It is the use of a simple but very effective sample roaster and a sample roasting system to preview the roast characteristics or a particular bag of greens, of a sample from a broker, or of a current of past crop in comparison. Then using this data, a roast master can set the best roast time and temperature for a beak profile production roast system.

Here are tools to develop a sample roasting system that can establish peak production profiles.

Looking at Green Growth and Production Standards

Green samples can be evaluated in two ways. One is by the aromatic information that they contain about freshness, process acceptability, and storage or shipping quality. This is gathered by nosing, literally, into the small bag or envelope that the green sample has come in. It becomes very obvious after very few samples that freshness and defects are easily discernible. The other observation is made by pouring the sample onto a white tray or plate. White is an extremely good background for close observation. You can use a magnifying glass for at least one pass over the beans. With magnification, defects such as mold or foreign matter like paint, dye, or oil become clear.

There are very good and useful coffee industry standards that can be referred to gather comparative information for the greens that are being examined. Both sets of standards are in the form of large posters that can be wall-mounted for a useful display, and cover in different formats the amount of defects by kind that will devalue a green sample. One set is available from the Green Coffee Association of New York, and is a group of three posters. The other is a Green Coffee Classification System, available from the Specialty Coffee Association of America, and its Resource Center. Both sets contain their own explanatory information to let you judge and grade a particular green sample according to the standards, and compare your results with the grade that was attached to the sample by the grower or broker.

Green Density and Size

Another part of the system is a comparative measure of green bean density. Studies show the direct relationship between greens with higher density and cup quality. Sivetz, Coffee Technology 262 (1979). Roast masters probably have already reached the same conclusion by intuition as they have felt, smelled, and looked over healthy, fresh crop greens from high elevations.

To develop an easy assessment of relative density, you can use the same cups you have on hand for cupping roasted samples and a good scale that will measure in grams. Pick one of the cups as your standard container. Fill it with the green sample, shake it well to eliminate extra space and fill and shake it again if necessary to bring the bean level to the top of the cup. Then weigh the sample in grams. You can choose a comparative sample from one of your known good quality beans or one of the growths that are generally found to be the most dense: Sumatra and Sulewasi. Coffee Technology 262. Measure, shake, and weigh in the same manner. This will give you a comparative base.

Screen size might provide some information about the character of the green sample you are looking at, if you thought the sample was of a different size than it is represented to be and you had invested in a set of screens and a rotap that mechanically agitates the screens properly. But far more important than the relative screen size is cup quality, and that is represented by overall quality of the beans, which most importantly means uniformity in size, color, freedom from defects, and fresh odor, so for our purposes, screen size is only of relative importance. Given high quality beans, cup quality can be sorted out by profile sample roasting rather than relative screen size.

Simple Sample Roasting

What is chosen here for sample roasting, a small commercial heat gun, available from any hardware catalog, is very effective for sampling, and, even though it relies on hot air roasting, it does a remarkable job. The information gleaned from this sample roaster can be transferred readily to the production roast profiles of either drum or air roasters. The heat gun sample roaster is also far less expensive. It is portable and uses the most available power source. You can take it to your broker's, to customers, or to the very plantation you want to sample if you luckily can go there yourself.

An off-the-shelf model of this roaster comes from Sivetz Coffee Company. The version pictured here has a modified chamber, which you can have built for you by any sheet metal fabricator, which slides over the nozzle of the gun, replacing the chamber that came with it. This modification allows the chamber to be completely open without any sort of screen at the top. The chamber height is at the level to which any of the roasting beans are able to rise during roasting, and still short enough to allow the chaff and debris to travel up and out in the hot air column.

The sample roaster holds approximately 60 grams of greens. The right amount can be determined easily. When it is on, you should pour beans slowly into the upturned mouth of the roaster. The amount is right when the mass or weight of the beans has nearly overcome the ability of the moving air column to lift and roll them.

Now you can see the entire bean mass as it begins roasting. The roast chamber is open and points upward at you so you can have an immediate picture of the relative uniformity of the development of the beans, comparing each one with every other one as the beans tumble past your view. This small roaster gives you a visual and aromatic picture of the entire mass of roasting beans throughout the roast. All you have to do is hold your head over the heat gun's roast chamber. You will experience a beauty and subtlety of roast development aromas that few people can. The upward airflow is an intense data stream for evaluation, as much as and more than is provided by a traditional sample drum roaster.

Chaff comes off as the beans expand and soften, before the beans reach the critical stage of pyrolysis, at 400 degrees F. The amount and uniformity of the chaff flight are very good indicators of the worth and finish of the processing that the beans have undergone, the uniformity of the beans themselves, and, probably, of their relative freshness. Often the freshest, most flavorful, and aromatic beans display very vibrant light green and yellow drying colors. This is the time that many storage and freshness defects are very apparent. And this is when lovely toasty and earthy aromas are noticed from high quality samples.

If you choose, you can measure temperature within the roast chamber by using a high temperature portable lab thermometer. Have a small hole drilled near the bottom of the expanding neck of the chamber where the bean mass tumbles as it roasts, and insert the thermocouple when you are roasting. Such a portable thermometer is available from Edmund Scientific.

Another tool to have handy is a stopwatch. You can time three critical points in the entire roast development, all of which are seen by looking down the throat of the roast chamber on top of the heat gun. You can establish a picture for yourself of normal roast development as your experience grows with various roasts.

  1. With the sample roaster first pop is noticeable by the singular popping of each of the beans, very decidedly loud and mechanical. The aromas now can be fruity, flowery, beefy, chocolaty, or spicy, or many subtle combinations.
  2. Second pop also is easily heard after an intervening quiet space, as heat builds up within the beans. It produces less determined by more universal pops within a very short time as the beans approach light roast temperature. You can make some critical decisions at this point about backing off the temperature to avoid the heavy end effect of deep blue smoky roasts, or you can go just the opposite and smoke 'em for a hefty, carbony finish, oiled and decidedly noir.
  3. You are also able to time the end of the roast with the stopwatch to see the relative development time of each degree of roast. Each of these roast profiles then awaits your judgment at cupping. Roast time and temperature on the heat gun can be controlled by opening or closing the vented aperture at the side of the gun's fan.

Peak Profiles Easily

To get peak profiles for each green sample, you can select the roast you want to try for the sample, say very light, medium, and medium dark, a set that suggests that the bean sample would be best represented by lighter roasts. Then you can roast away, cool, and cup, selecting or rejecting the results and finally establishing the peak production roast profile you have uncovered.

Roast profiles that are at the peak for a particular sample can further be identified by using a roast color analysis system, such as the one by Agron, available in the least expensive forma s a set of roast color tiles, which are related to roast degree designations that can be used as reference points in production roasting. This set is available from the Specialty Coffee Association's Resource Center.

Using the sample roaster/heat gun and the other tools for green sample analysis, you can roast samples under broad profiles and use all the information about the green samples to set the peak profiles which genuinely characterize your personal roast style as a master roaster. And as you enjoy sample roasting for peak profiles and cupping from the array of samples before you, you can say: "What superbly wonderful work it is to be a roast master!"

© 1999 by John Gant

 

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