Thursday, October 25, 2018

Roasting Coffee with a Hot Air Poppcorn Popper

There are many methods of roasting your own coffee. In fact,  roasting your own coffee on an as-needed basis using a stove, oven or fire to was common until relatively recently. I have used several machines for roasting coffee at home. Today one of the fastest and easiest methods of roasting coffee is using a hot-air popcorn popper and the method I use most often myself (although I have purchased two dedicated roasting appliances over the years). Here I will share some details about the roasting set up that evolved over almost 16 years of recreational coffee roasting.

The Beans

Today's roast is Timor Leste Lacao Village from Sweet Maria's. They are my favorite supplier of green coffee and a great source of information about roasting and the history of coffee.

The Roaster

My current roaster of choice is a donated vintage popcorn popper that has worked well for several years. Often poppers are available in thrift shops. If you ask friends and family I expect you will find someone who is happy to give you one that has been sitting unused in the cabinet for years.

I have had the power switch fail on a couple of poppers over the years. Now I connect the popper and cooling fan to a switched power strip so I can turn them both off and on at the same time. In addition to eliminating the popper switch as a failure point, it also saves the hassle of wrestling the popper looking for the switch. One detail I like about this popper is the open-topped discharge shoot that works well with the vent used in my setup.

Roasting coffee produces chaff (a piece of the parchment-like wrapper that comes loose from the bean during roasting) and smoke and keeping both of these under control makes roasting much more pleasant. My approach is to keep the popper a box with a top-mounted vent connected to a bilge blower that exhausts through an insulated panel installed in a window in my garage.

Power for the bilge blower comes from an adjustable power supply on my workbench. By turning down the power to the blower and slightly closing the flaps on the box, I can improve how quickly the roaster warms up during cold weather. It is no fun waiting for a slow roast to finish in an unheated garage.

Automated Control Options

Without hacking into the electronics of the popper, this setup still offers two clear options for automated control. The first option is to use a hobby RC servo to control a vent (flap or sliding window) on the side of the box. The idea is to close the vent until and operate the roaster in the sealed box until the interior temperature of the box reaches a specific threshold (100 F?) to get the roast started quickly, even in cold weather.

The second option would be to add PWM control of the blower to run at be off or run at low speed until the temperature reaches the desired threshold. Again to help the roast comes up to temperature quickly in even the coldest temperatures while still ensuring the fan is on to vent smoke and chaff outside once the roast gets going. 

Roasting Technique

I start the popper and pour green beans into the chamber until the beans just stop swirling (maybe just a little extra). I will then give the roaster a few shakes (it might take a minute) until the beans are swirling on their own. The goal is to use as much coffee as the popper can circulate.

The bean will go through many stages during the roast. Where you stop the roast depends on the type of bean and the degree of roast that you want. The article below outlines the differences between the stages of roast.
Stages of Coffee Roast

As the beans warm the coffee beans will begin to change color and begin losing some of their chaff. As the beans begin to roast you will hear a popping sound, the first crack, and the chaff will come off of the beans very quickly. I like to stop the roast when the first crack has just finished. This is generally described as a City Roast. For this batch, I stopped the roast at a little under 6 minutes.

I feel most coffees reach their peak of flavor between the end of the first crack and the very start of the second crack. If you want to roast past City Roast the quickness of your cooling method becomes more critical as the roast begins to be exothermic and can coast for some time after being removed from the heat. If your cooling is too slow it is very easy to overshoot and get a darker roast than you intended.

Cooling the Roasted Coffee

I cool the roasted coffee by dumping into a wire mesh colander setting on a fan aimed straight up. I found that cooling time can be shorted by bending a dome into the bottom of the colander and using a little painter's tape to direct the airflow inward. With this set up the beans are cool to the touch in less than two minutes.

The dome keeps the beans away from the center of the fan that has low airflow. Before the dome, I had to shake the beans around to ensure even cooling. 

This batch yield 116 grams, or just over 4 ounces, of roasted coffee. The beans get lighter as they lose moisture and volatiles during roasting so this probably started out as close to 5 ounces of green coffee.

I usually do at least two batches of whatever I am roasting. This usually means two batches of caffeinated and two batches of decaf. This is just the right amount to fill the jars that I like. Coffee brewed with beans fresh from roasting tastes great to me but many types of bean will improve in flavor with a rest of 6 to 48 hours.

If you would like to try roasting yourself, I recommend starting with a hot-air popper and coffee sampler from Sweet Maria's. Try the half-decaf bundle and you may be surprised at how good decaff coffee can taste. My favorite everyday coffee is half decafintaed Indoneasian and half caffeinated Yeman or Ethiopean. I also like having decaf on hand for the occasional evening cup of coffee.

Hot Air Popcorn Popper

I hope you have learned something that helps you improve your coffee roasting.

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