Coffee Roasting

Coffee is roasted to removing toxins, enhance taste and concentrate aroma. An unroasted coffee bean starts out as a green coffee bean, it is very hard, has little smell and contains compounds that are bitter to the taste. The coffee beans must be roasted in order to change the physiology and chemical make up of the green coffee bean. The roasting process involves exposing the fresh coffee beans to a hot gas, another method which is still used by some small roasters and can be used at home is laying the beans out on a hot metal surface; the resulting chemical and physical changes lead to coffee that tastes and smells wonderful.

 

The coffee roasting process
Many different mechanisms have been developed to roast coffee in order to create better tasting coffee. Nearly all methods of coffee roasting use the same basic processes. Initially the green coffee bean is heated up; this results in evaporation of water in an endogenous way. Once the coffee bean reaches about 160oC exogenous chemical reactions take place, these reactions reach their ultimate potential at around 220oC. Further increases in pressure within the bean lead to carbon dioxide and water vapor being forced out of the bean, and a lowering of coffee bean density. This in turn leads to an expansion of the coffee bean in size, and a splitting and popping of the bean. Once the bean has been roasted long enough (from nine to fifteen minutes depending on the roast required), it is rapidly cooled by use of water or cool air.

 

Changes in the coffee bean during roasting
The process of roasting coffee results in many changes in a coffee beans appearance: The bean changes from green to brown or almost black in colour; The density will decrease by around 40%; there will be an increase in volume by almost half the size of the bean again; and there will be a massive loss (up to 85%) in water content.

 

Different methods used in commercial coffee roasting
Usually coffee beans are placed in either a horizontal rotating drum, or a vertical rotating drum, that has paddles to move the coffee around. They are then exposed to hot gasses, which reach temperatures of almost 450oC when they enter the drums, but which cool when mixed with the coffee beans. The coffee beans are then left for between 9 and 15 minutes until they have reached the required roast. In general the greater the ratio of Gas: Coffee then the quicker a bean can be roasted, and the lower the temperature that roasting can be achieved.

 

One of the most common ways of commercial coffee roasting is that of Fluidized Bed Roasting. In fluidized bed roasting coffee beans are given bursts of high velocity gasses from beneath; this enables the beans to move across the fluidized bed in a controlled way, and results in a high quality end product. During the roasting process coffee beans increase in size and therefore it is essential to modify the speed that the gas comes out in different parts of the machine to ensure uniform roasting.

 

Other methods of commercial coffee roasting include Fast Roasting. In the fast roasting process  coffee beans are rapidly roasted, and it can take as little as one minute to completely roast the beans (it may take up to four minutes). Fast Roasting makes use of a high Gas to Coffee ratio. The coffee from the Fast Roasting process typically has a higher brew strength than normally roasted coffee; it is also notable that the beans are also greater in both density and volume.

 

Many different methods that are used to roast coffee, the procedure has a large impact upon the way a coffee looks and tastes. The art of coffee roasting transforms a hard, aromaless green bean changing it into the deep smelling, good looking, and great tasting coffee that we all love.

 

 

 

 

 

The different roasts are determined by timing. The longer coffee is roasted, the darker and less acidic it becomes. Depending on the temperature, type of coffee and the equipment, roasting time is usually between 9 and 15 minutes.

 

The 6 most common roasts are:

 

Light Roast: Coffees roasted for a shorter time or at a lower temperature may retain a little of the green flavor, these beans are a light brown color, smooth tasting and often used in a traditional breakfast blend coffee.

 

Medium Roast: Prefered as a traditional American roast these coffee beans have a medium brown color and all traces of a green taste are removed but the coffee beans have not yet relesed ther oils and do not have the sheen of the darket roasts. Medium roast coffee is used as a base form many flavored coffees.

 

City or New England Roast: Before Starbucks changed out tastes to deeper roasts this was the most popular coffee roast. Hard to achieve, it is between the medium and full city roast. The nutty flavors come out with no darker roast bitterness or smokey taste.

 

Full City Roast: This is the most common roast denoting the full development of coffee flavor. It is dark brown with few traces of oil on the surface of the bean. The flavor is caramel to chocolate like with some hints of smokiness.

 

French Roast: Very dark brown with large amounts of oil on the beans. It is bittersweet, smoky and pungent.

 

Italian Roast: Coal black and soaked with oil, amazingly aromatic before brewing with more pronounced characteristics of the French Roast and lower acidity.