How To Roast Coffee Beans

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About Coffee And Why It Is Roasted

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Last update on 2020-05-06 / Affiliate links / Images from Amazon Product Advertising API

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Coffee is a small red fruit that must go through many stages to become the tasty brown bean we process in a grinder before brewing the drink we all know and love. 

Most good coffee is first wet processed to remove the outer skin, pulp (which is actually fermented away), and inner parchment skin. 

Then 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 dry pinto bean – it can be stored for a long time yet still become a fresh and aromatic food item after it is roasted or cooked and then introduced to your espresso machine.

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- in short, undrinkable. 

The relatively simple act of roasting coffee used to be a common home task, but in todays modern society it became shrouded in mystery as the process was taken over by large companies in the late 1800’s. 

The growing popularity of gourmet coffee and single-serve coffee makers has sparked an interest in reviving the traditions of roasting coffee at home.

Fortunately, today we have the advantages of modern knowledge and devices like pour over coffee makers to make coffee roasting easier than it was over a century ago.

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 truly delicious coffee for your drip coffee maker.

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. 

Just one week from the time it is roasted, the coffee has already started to lose some of its best flavor and aroma- the best reason to roast your own!

Basic Requirements For Roasting Coffee

Regardless if your chosen coffee is organic or not, to successfully roast your own 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 to a fully automated roasting appliance. 

Beans must be heated to temperatures of 370 oF to 540 oF. Faster air currents permit lower temperatures.

The coffee beans must be 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 and disposed of properly.

Coffee Roasting Methods

Although a relatively simple process, roasting your own coffee does take some practice to develop consistent results that will meet your expectations for an excellent cup of coffee. 

There are several factors which will determine the method you will want to use for roasting your own coffee – and yes, all of these add to the seed-to-cup carbon footprint – but less than you may think.

Some methods require more attention to detail and more of your time but are less expensive; others require a larger investment in equipment but will save you time. 

The instructions here are a summary only and are not intended to be the sole source of knowledge, especially when you are investing more in responsibly farmed coffee beans from the outset.

For more detailed roasting knowledge we recommend the book “Home Coffee Roasting, Romance and Revival” by Kenneth Davids.

Using a stovetop roaster

It is recommended that you purchase a crank style popcorn popper such as a whirley-pop but 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 (unless you want curry flavored coffee!), 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.

Note: The use of a candy or deep fry thermometer will greatly increase the accuracy of the roast and is highly recommended. A good basic thermometer is available in our online store.

  1. Start by heating the frying pan or roaster on the stovetop to a medium setting, or until temperature reaches about 475 oF. Add up to 8 oz. of green coffee beans and close the lid and begin turning the crank (or stirring) constantly.
  1. 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.
  1. About a minute after the first crack check the beans color frequently (once a minute) until the beans have reached the desired roast color.
  1. 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.

Fireplace, Campfire, or Barbecue:

Back in the days of the old wild west many frontier travelers carried green coffee and roasted it as they needed it. 

Sometimes the only method available was a cast iron frying pan over an open fire. With patience and practice, this method can produce a nice tasting roasted coffee, although it is nearly impossible to get an even roast. 

The process is basically the same as the stovetop method, above. A fireplace popcorn popper is an easy way to roast because the long handle helps keep your hands from getting burned and the lid keeps the heat in and helps to maintain an even temperature. 

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If roasting over an open fire, it is important to wait until the flames die down and there is a good bed of hot coals. 

Use the methods outlined to determine the right time to remove the beans from the heat and cool them down.

Fluid Air Bed Coffee Roasting Machines

Fresh Roast SR540

Purchasing a home coffee roasting machine is a more expensive option than the other methods in this article, yet the process is more automated and less messy. 

With the fast moving hot air of a fluid air bed roaster a very even roast is attainable. 

These 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, pictured right, which retails for about $90.

Fresh Roast SR540
98 Reviews
Fresh Roast SR540
  • Real-Time Temperature Display
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Last update on 2020-05-06 / Affiliate links / Images from Amazon Product Advertising API

Gas or Convection Oven Roasting

If you have a good quality gas oven or a high temperature convection oven (that heats to at least 450 oF), you can roast coffee in larger quantities in a few simple steps. 

Oven roasting usually produces a somewhat uneven roast because there is very little air flow, but the taste can be rich and complex for this very reason. 

You will need a flat baking pan that has been perforated with many small holes that are close together and a raised lip. 

You can find such a 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- 540 oF. 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.
  1. 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.
  1. 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.

Guidelines For All Roasting Methods

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 some 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, this method 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 at the bottom of this page 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 even after the heat source is removed. 

To speed the cooling process if roasting with an oven, stovetop, or 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 even 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). 

In the absence of an exhaust fan, 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.

Coffee Roast Style Chart

Roast ColorName of RoastBean SurfaceAve. Bean Temp.(at end of roast)AcidityBodyAromaSweetnessComments
 Light Brown/ CinnamonDry380- 400 oF“First crack”HighWeakMediumLowVery light roast that is rarely used. Can taste grainy and sour.
         
 
Medium light Brown/ American
Dry400- 415 oFHighFullFullMildCommon roast in eastern US
         
 Full Medium Brown/ CityDry415- 435 oF“second crack”HighFullStrongMildCommon roast in western US
         
 Medium-dark brown/ Full City/ Viennese/ Light FrenchSlight oily surface435- 445 oFMediumVery fullStrongStrongCommon roast in Pacific northwest
         
 Dark brown/ French/ EspressoShiny surface445-460 oFLowFullMediumFullCommon roast for France and Italy
         
 Very dark (nearly black)/ Dark French/ SpanishVery shiny surface460- 480 oFvery lowWeakMildLowBurned tones are distinct or even dominate. Not popular in the US.

*Note: the above colors may not be accurate due to color changes that can occur with individual computer and web browser settings.

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