Coffee Beans -
    Home Roasting

Rather than buy ready-roasted and powdered coffee sachets for brewing, it is quite possible to roast green coffee beans at home, and in doing so to produce your own very individual result.


About Coffee And Why It Is Roasted

Coffee is a small red fruit that must go through many stages to become the tasty brown bean we all know as coffee. 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.


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 it today's 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 has sparked an interest in reviving the traditions of roasting coffee at home. Fortunately, today we have the advantages of modern knowledge and devices 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 flavour essences that make a good coffee. The colours 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 flavour 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 flavour and aroma - the best reason to roast your own!


Basic Requirements For Roasting 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 to a fully automated roasting appliance.


Beans must be heated to temperatures of 370 F to 540 F. 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 properly.


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 F), 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 F. 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.




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:


Fresh roasted coffee

Colour: 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 flavour 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 flavour 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 flavour and aroma. The rest period allows excess CO2 to dissipate and permits the coffee bean chemistry to stabilize.



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