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The New Home-Brew

Coffee Bean Roasting is becoming the new home-brew. Coffee is a small red fruit that must go through many stages to become the brown bean we all know (and love) as coffee. Most good coffee is first wet processed to remove the outer skin, pulp (which is actually fermented away) and inner parchment skin. The inner seed, or bean, is dried and becomes the green coffee that is shipped and stored around the world.

Green coffee is a lot like a dried pinto bean- it can be stored for a long time and still become a fresh, aromatic food item after it is roasted or cooked. The final step to make the coffee bean ready for brewing coffee is to roast the green beans. Without roasting, a beverage made from the green coffee bean would be bitter and extremely acidic and basically undrinkable. 

Roasting your own coffee might be easier than you think.  You can roast beans in your oven, a popcorn popper or go all-out with a roasting machine.  During roasting, the beans “crack,” meaning the beans dry out and some sugars from the beans are caramelized, which gives the beans its flavor. You will hear a popping sound from your beans, known as the first or second crack.  The first crack occurs at about 380 degrees Fahrenheit, while second crack happens around 415 degrees.  The hotter you roast your beans, the darker the roast. Lighter roasts are more acidic and medium roasts (around the second crack) are popular in the western United States.

During the roasting process the green coffee changes dramatically. The process of roasting forces water out of the bean, causing it to dry and expand in the process. Some of the natural sugars in the bean are transformed into CO2 gas and others are caramelized into the complex flavor essences that make a good coffee. The colors darken and at the end of roasting the bean is about 18% lighter in weight and 50 to 100% larger than when it was green. After roasting the coffee continues to “degas”, emitting CO2 which helps protect the delicate flavor and aroma of the coffee. 

To roast your own coffee at home, the following basic requirements must be met for a successful roast. There are several methods available to home roasters that meet these requirements, from a stovetop popcorn popper (a crank style popper is highligh recommended) to a fully automated roasting appliance. 
  • It is best if the coffee beans are in constant motion to prevent scorching or uneven roasting. 
  • The beans must be cooled quickly to prevent over roasting.
  • Roasting coffee produces smoke which must be vented properly.
  • The roasted beans shed the outer skin during the roasting process and the light weight skins (called chaff) can make a mess if not handled properly.

Roasting in an Oven

If you have a good quality gas oven or a high temperature convection oven (that heats to at least 450oF), you can roast coffee in a few simple steps. Oven roasting usually produces a somewhat uneven roast because there is very little air flow, however the taste can be rich and complex for this very reason. You will need a flat baking pan with a raised lip that has been perforated with many small holes that are close together. You can find this type of pan at many gourmet kitchen supply stores, or you can make one with a sturdy baking sheet an a power drill with a 1/8” metal bit. Holes should be spaced about 1/2” apart and small enough so the beans do not fall through.

  1. Preheat oven to 500 - 540oF. Put the green coffee in pan so the beans are one layer deep and close together and covering the entire surface of the pan. Place the pan on the middle oven shelf.
  2. Roast for 15 to 20 minutes, or until desired roast is reached. If roast takes longer than 20 minutes, you should roast at a higher temperature. Every oven is different, so it may take several batches to achieve the best results. By taking notes, you should be able to duplicate these results every time. 
  3. Once the beans are roasted to your satisfaction, immediately remove from heat and pour into a large metal colander to cool. Toss or stir the beans to remove excess chaff and speed the cooling process.

Stove Top Roasting

As mentioned above, is recommended that you use a crank style popcorn popper such as a whirley-pop,  however this method can be used with a simple old fashioned cast iron skillet or heavy frying pan. If using a frying pan, make sure to use one that does not have absorbed cooking smells and be prepared for a somewhat uneven looking roast. Roasting on the stovetop takes longer and will produce a roast with more body and deep notes but will lose some of the bright notes and aroma of a faster roast such as a fluid air bed roasting machine.  The use of a candy or deep fry thermometer will greatly increase the accuracy of the roast and is highly recommended.  

  1. Heat the frying pan or roaster on the stovetop to a medium setting, or until temperature reaches about 475 oF. 
  2. Add up to 8 oz. of green coffee beans and close the lid and begin turning the crank (or stirring) constantly.
  3. Continue stirring. Beans must be agitated constantly for an even roast. At a minimum, beans must be stirred every 30 seconds. In 4- 7 minutes the beans will start to make crackling sounds. At this time coffee smelling smoke will start to appear. If you have a fan hood, turn it on now, or open the window.
  4. About a minute after the first crack check the beans color frequently (once a minute) until the beans have reached the desired roast color.
  5. Once the beans are roasted to your satisfaction, immediately remove from heat and pour into a large metal colander to cool. Toss or stir the beans to remove excess chaff and speed the cooling process.

Roasting Machines

Purchasing a home coffee roasting machine is a more expensive option, however the process is more automated with less mess. With the fast moving hot air of a fluid air bed roaster a very even roast is attainable. The roasters operate on the same principal as a hot air popcorn popper: air is heated and then blown directly over the beans. This heats the beans and keeps them in constant motion, resulting in a faster, more even roast. Coffee roasted by this method usually has a good strong aroma and bright flavor notes, but can sometimes lose the deeper notes of a stovetop or drum roasted coffee. Currently there are several models of home roasting appliances available, including the FreshRoast, which retails for about $90.

Guidelines For All Methods of Roasting

The most important consideration when roasting your own coffee is knowing when to stop the roast. As you become more experienced you will be able to stop the roast with more precision while relying on the following methods:

  • Color.  Start with roasted coffee that is roasted to the style you prefer. Use these beans as a guide, or refer to the chart at the bottom of this page.
  • Temperature. Use a candy or deep fry thermometer to measure the temperature of the beans while roasting. If using a roasting machine, a thermometer is not necessary.
  • Smell.  When the beans are nearly done the smell will change from a wet grassy vegetable smell to a coffee smell. As you gain experience, you sense of smell will become more refined.
  • Sound. Once the beans get hot enough they start to crackle as the water in the coffee turns to steam and is forced out. There are two distinct stages of cracking, commonly referred to first and second crack. See the chart below for temperature ranges for these two important stages.
  • Time.  All other factors being equal, such as type and weight of the beans and the roasting temperature, you can duplicate previous efforts by timing the duration of the roast and recording this information for each type of green coffee you roast. This method is especially useful when roasting coffee in an oven or with a coffee roasting appliance.

Cooling the Beans and Removing Chaff

As soon as a batch of coffee is done roasting, it should be cooled as quickly as possible. The coffee beans will continue roasting from residual internal heat. To speed the cooling process if roasting with an oven, stovetopor campfire method, dump the hot beans into a colander immediately after removing from the heat source. If you have a large quantity of beans, using 2 colanders is more efficient. Pour the beans back and forth between the 2 colanders slowly. If you do this outside and there is a slight wind you can effectively remove the chaff this way as well. It is not necessary to remove every bit of chaff as it will not affect the flavor in small quantities.

Venting the Roasting Smoke

Roasting coffee produces a bit of smoke, and this will have to be vented if you roast coffee indoors. A stovetop exhaust fan is typically adequate to vent smoke from most roasting efforts unless a large quantity of coffee is roasted very dark.  The darker the roast, the more smoke is produced.  If an exhaust fan is not available, a portable fan in front of an open window will usually take care of the smoke.

Resting & Degassing: The 24 Hour Wait to Prime Time

Fresh roasted coffee reaches its peak flavor and aroma about 24 hours after resting. A 24 hour rest period is not necessary but is preferred by many coffee lovers to allow the beans to fully develop their flavor and aroma. The rest period allows excess CO2 to dissapate and permits the coffee bean chemistry to stabilize.  


Roasting chart from Seven Bridgest Cooperative website, a source for organic brewing ingredients

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