Home Roasting – Part 2

2010 July 2

I’ve started doing small batch home roasting with  a new HotTop coffee roaster. It is a pretty advanced drum roaster that operates similarly to a shop drum roaster. The roasting vessel is a small perforated drum with a capacity of 250gr (about 8oz) of green coffee. Heat is provided by an electric element and there is a variable speed fan used to control airflow through the roaster. Roasted coffee is cooled in a separate cooling tray that stirs the coffee and has a separate cooling fan. The whole process is run by a control system run by a micro-controller which has easy to use controls and a great display for monitoring the progress. The HotTop is solidly built in and is extremely well designed.

The perforated roasting drum is made of stainless steel and has a welded wire agitator to move the beans front to back within the drum. The loading of the drum takes place at the rear. Beans are dropped into the cooling tray from the back, as well, via a solenoid operated ejection door. Temperature measurements are taken at the back of the drum, while the front of the drum has a large glass window to watch the beans roasting.

Starting the Roasting Process

The first thing I did was read the instructions. As a guy, it is against my nature to read instructions, but a coffee roaster has a reasonable chance of catching fire if improperly operated and maintained. Lawyers had definitely been involved in the verbiage as “no brainers” such as “do not submerge the roaster in water” were included with more likely operator issues. The documentation is well written and the HotTop website yields even more helpful and advanced material (including step-by-step guides on replacing parts and doing repairs).

The most important item to have, other than the roaster, is some top quality green coffee. I purchased five pounds of Guatemalan Finca San Diego Buena Vista (St. James Beautiful View Farm) from SweetMaria’s. It seemed to be a good choice in that it could make both an excellent coffee for drip and yet be roasted slightly darker for a single origin espresso. Inspecting the beans, I found them to be of uniform size and free of defects: a clean preparation.

The roaster is designed to use a fixed batch size of 250gr. The instructions state that you can vary the batch size slightly to affect the roasting rate. I decided to go with the standard batch and weighed out the exact amount.

After powering the roaster up, you can select to run it manually or to run a profile automatically. A profile is essentially a program of data points for that set the roasting path. These may include time, temperature, fan speed, heater output, etc. The HotTop comes with a standard profile that can be modified as you roast or you can roast manually (adjusting the variables over time). If you roast manually, the roaster can save your profile for repeating in the future. This is handy if you want to standardize a roast of a particular coffee. The roaster can save up to three custom profiles in addition to the standard one.

I selected the standard profile, which has an ending time of  18:00 minutes at a final temperature of 420F (whichever comes first). The profile changes the fan speed and heating element power level over time during the various phases of roasting.

In all cases, the starting point for a roast is 167F. The roaster either heats up or cools down (after a roast) to hit this temperature. Since the profiles are based upon a known starting point, this is very important. The display shows “P H” until the starting temperature is achieved then beeps to indicate loading time.

At the loading beep, you remove the upper door and insert a black plastic funnel. Pour the green beans into the funnel, down the chute and replace the door when you are finished. The roasting process has begun.

Monitoring and Adjusting the Roasting Process

The roasting process starts out quietly with the tumbling of the beans in the drum being all you hear. Observing the roasting process to make adjustments is accomplished in four ways. First, the beans can be seen though the window at the front of the roaster (color changes,chaff, etc.). Second, the temperature, time and system variables can bee seen on the display. Third, we listen for certain tell-tale sounds (first crack, second crack, audible alerts). Lastly, we can smell the changes occurring as the beans roast.

Early in the roasting process, not much appears to happen. The beans are starting to dry out as the moisture escapes and the color turns from jadite green to straw colored. The aroma changes from grass/alfalfa to bread baking.
The control panel and display show the minutes remaining for roast completion and the current temperature. It also shows the fan speed  (in this case OFF) and the heating element power (in this case 100%). At any time you can adjust any of these variables to deviate from the standard profile. I did change the ending temperature to 424F because I am roasting this batch for single origin espresso.

The first audible stage is called “first crack”. It starts out with a few singular sharp popping sounds and then builds to a crescendo and trails off later. During this phase certain chemical reactions take place and the chaff (or silver skin) detaches from the bean as the bean expands in size. The chaff is removed from the drum by applying air and collecting it in a tray below. At this point the aroma smells like coffee and smoke rises from the vents of the machine.

Ending the Roast and Cooling

The roasting process accelerates from this point on and vigilance is required. The color of the bean changes rapidly from cinnamon to milk chocolate brown and the beans continue to expand. Soon a second audible stage begins called “second crack”. Similar to first crack, but more subtle, the coffee undergoes major changes in flavor and color. The aroma becomes more bittersweet and the amount of smoke increases as the color of the beans go towards bittersweet chocolate. If you continue further, the smoke becomes more pungent, the beans become darker and the oils come to the surface. You cannot roast them dark enough to become completely black (which is ruining the beans anyhow) because the HotTop has a preset cutoff at 428F which can not be adjusted.

At 424F, the profile ended and the roaster automatically ejected the beans. At this point the drum continues turning to drive all of the bean out of the drum, out the ejection chute and into the cooling tray.

The cooling tray runs for 5 minutes. The stirring blades are driven by a motor that moves the beans both clockwise and then counterclockwise. A separate fan draws cooling air through the beans.

After the beans have cooled, you reweigh the coffee to calculate weight loss during roasting. In this case, the ending weight was 204gr and the charge weight was 250gr, which is a weight loss of 46gr or 18%. This would be classified as “Vienese Roast”. The range in which most roasting is done is a 15% to 19% weight loss and that corresponds to stopping the roasting process just before second crack through nearing the end of second crack and degree of roast “City Roast” though “French Roast”.

At this point, the roaster can either be turned off or start another batch. If starting another batch, the roaster will cool itself to 167F before allowing the roasting process to begin.

The Final Result

The photo above show the green coffee and the roasted coffee. The expansion of the beans is obvious. Also note the silver skin on some of the green coffee prior to roasting and the tiny amount left in the groove of the roasted coffee. At this point, the coffee should be allowed to rest an de-gas for a while (varies from 1 day to 3 days depending on how the coffee will be used). De-gassing is the natural release of carbon dioxide gas that builds up inside the cells during the roasting process. Once rested, enjoy the coffee!

Some Conclusions

The HotTop is a great little drum roaster. It is well made and easy to use. The control system allows profile roasting and manual control which enables one to roast coffee with a similar level of control that a commercial shop roaster offers. The separate cooling tray is a necessary feature that most home roasters do not have. Parts and technical support are readily available. If you don’t mind spending the money (about $700), it is an excellent investment. If $20 is more your budget, in my next post we will roast with a hot air popcorn popper!


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