Green coffee beans keep for several years; however, once roasted they lose almost half of their flavour within a few weeks. After they have been ground, they start to lose their flavour relatively quickly.  Consequently, the best way to have delicious full-flavour coffee every day is to buy some green beans, roast them yourself and grind them immediately before brewing your coffee. For most people that's too much like hard work; so, the next best thing is to buy freshly roasted coffee from a specialty roaster such as Abyssinica. All of our beans are roasted on the same day as they are shipped and can be ordered ground or whole.

Much is said about the types of beans that produce the best coffee, but the roasting process that brings out the aromatic essential oils is rarely mentioned. This is an oversight because when it comes to brewing delicious coffee, quality beans and precision roasting are opposite sides of the same coin. Top quality Arabica beans can be ruined by poor roasting while inferior Robusta beans can produce an acceptable cup of coffee if roasted to perfection. The roasting process is an art, and skill at roasting can only be developed by careful experimentation and sampling. At Abyssinica we only use top quality Ethiopian Arabica beans, regarded by most roasters as the best available, and every batch we receive, undergoes several trial roasts to determine the optimum roasting conditions for it.

The chemistry of coffee roasting is complex, and although it has been extensively studied by scientists, is still not completely understood. Basically, the beans give up some of their moisture, shed their outer skin known as chaff, lose about 10% – 15% of their caffeine and some of their sugars are burned or caramelised. In addition, the oils that give coffee its distinctive flavour and aroma are produced.

Stages in the Roasting Process

200 - 250°F internal bean temperature

This stage is referred to as the yellow stage and is reached after a few of minutes of roasting.  Steam starts to rise from the beans as they start to give up their moisture and a slight change of colour can be detected along with a grassy or damp straw smell.  It is surprising how different the smell of different beans can be at this stage even though it is only water vapour that is being given off.  At this time, the beans are undergoing an endothermic reaction during which they absorb heat very quickly.

250 - 300°F internal bean temperature

The next stage is the light brown stage which is reached after five or six minutes of roasting.  The amount of moisture being released starts to decline and the beans turn a light toasted colour giving off a baked-bread smell. The endothermic reaction continues and gains momentum as the beans lose the last of their moisture.

300 - 370°F internal bean temperature

As the internal temperature reaches 350°F an exothermic reaction takes place in the beans which begin to release their heat energy in a stage known as first crack.  This usually happens between about 7 - 12 minutes of roasting but it depends on the particular beans and the roasting equipment being used.  At this time, the beans expand, moisture and carbon dioxide are released, and the chaff which coats the beans separates and is removed in most roasters.  Sugars begin to caramelise and the oils that give coffee much of its flavour begin to form.  The beans begin to darken quickly and their unique fragrant aroma is given off.  Some beans sizzle quietly at this stage snap, crackle and popping like a bowl of Rice Krispies, others explode thunderously making loud bangs. The beans need to be watched carefully from this point as the optimum roast for most Ethiopian coffees is approaching.

370 - 420°F internal bean temperature

Approximately 15 minutes into the roasting process the beans begin to enter the City Roast stage.  Although this is not necessarily the optimum time to stop the roast, it usually provides you with the best opportunity to sense the unique origin character of the beans.  The beans are a light brown colour at this point.

420 - 450°F internal bean temperature

The next stage is the Full City Roast stage where the second crack takes place. Second crack is more volatile than the first crack and small pieces of some beans explode like shrapnel. This is because the beans contain some cellulose that reacts readily to heat and some that does not. Second crack can continue for a couple of minutes with the beans that crack first starting to turn quite dark. Smoke begins to be produced immediately second crack starts and becomes more profuse the longer the roasting process continues from this point. With a delicate coffee like Yirgacheffe, a good time to terminate the roast is about one minute after second crack begins.  All of the coffee we roast at Abyssinica is terminated between 1 - 3 minutes after second crack begins as this gives us the optimum range of roasts for Ethiopian beans. Any longer and the essential oils will start to be burnt off. We like to see the beans glistening with oil when they come out of the roaster.  This indicates that the coffee will have a rich flavour and aroma.

450 - 470°F internal bean temperature

Following on rapidly is the Vienna or Continental Roast where origin character begins to be replaced by roast character. The beans start to become very dark and their structure begins to break down as the aroma turns even more smoky.  Although this roast is popular in some parts of the world, much of the unique character of high quality Arabica beans is lost at this stage.  However, a small quantity of this roast could add to the complexity of a blend.  On its own, coffee roasted to this stage will be a little thin and will have a noticeable bitterness.

470 - 500°F internal bean temperature

The cellulose bean structure begins to carbonise during the next stage, known as the French or Italian Roast.  The beans expand further but loose mass as the aromatic compounds and oils are burnt off.  The beans will have a hollow sound and feel like charcoal.

500 - 530°F internal bean temperature

At this stage: the Spanish Roast, virtually no compounds contributing to flavour are left in the beans and the resulting coffee will taste very thin.  The beans will be jet black, and, once again, will feel like charcoal.   

Grinding

After roasting, the beans have to be ground so that their flavours can be easily absorbed by hot water. However, care must be taken not to grind the beans too excessively as this can cause the oils to evaporate and the resulting coffee to taste bitter and acidic. The beans are better ground between grinding stones than in a blade grinder as oils can be destroyed by the rapidly revolving blades. Only enough coffee should be ground for immediate brewing as flavour begins to be lost after grinding. However, if this in not practical the ground coffee should be stored in an air-tight contained and kept in a cool place. This will preserve the freshness for up to a fortnight without a huge lose in flavour. However, ground coffee stored for more than a month, even in an air-tight container, will undergo a discernable loss in flavour. Different methods of brewing require different grind consistencies.  Here is a brief guide:

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Last modified: 02-Mai-2008