Coffee of various origins is usually blended in the trade in different proportions so as to make a cup with varying acidity and taste characteristics. Several batches of coffee are likely to taste different to each other because it is a natural product. Blending is one way in which constant quality can be achieved. With more than 100 coffee growing regions in the world, each producing beans with distinctive characteristics, proper blending is obviously essential to balance the flavors needed to create a superior espresso. A single coffee bean will generally not possess the complexity necessary for a great espresso. Many espresso blends will contain 3-7 different types of beans. Roasters still argue which should come first, the roasting or the blending. Some people believe that roasting each variety separately and then blending will maximize its flavor and produce the best result. While others believe that if roasted together the aromas of the different combinations are homogenized. Blending before roasting can certainly be difficult in that the homogeneous roasting of beans of different size, weight, and country of origin has to be achieved.
When green, coffee keeps for a long time, provided it is protected from dampness. Keeping it, actually improves it. It is entirely devoid of smell. To release the aroma, coffee has to be roasted, an operation which many coffee lovers insist on performing themselves. A good roaster must be part artist and part scientist, to maintain quality and consistency.
In the development of flavors, roasting is probably the most important step. Well-roasted coffee should be varying degrees of brown, but never black. If not sufficiently roasted, it produces a colorless infusion, and is rough and astringent. If over-roasted it produces a black drink, bitter and unpleasant. In the roasting process coffee beans undergo many hydrolytic reactions that lead to the formation of the substances responsible for their sensory qualities, accompanied by important physical changes. It is during the roasting that the sugars and other carbohydrates within the bean become caramelized, creating a substance that is known as coffee oil. Technically, this fragile chemical is not actually oil, but it is what gives the coffee its flavor and aroma.
The modern machines used for roasting evolved in 1200 AD from crude stone vessels. The first cylindrical design was developed in 1650 which are now used by major coffee companies. In the 900 years that coffee has been roasted, the basic concept remains the same: create a flavorful, evenly roasted bean from the green coffee of the fields. During the industrial roasting process a small quantity of sugar molasses or various other products is sometimes added, to ‘coat’ the berries. This coating, which is permissible by law, gives the berries a better color and more shiny appearance. It helps prevent the loss of aroma and provides an advantage to the merchant of increasing the weight. Unfortunately this system allows some producers to use inferior quality or damaged grains. It is important to watch out for this when buying coffee! Specialty coffees, on the other hand, are generally roasted in small batches. The two most common roasting methods are drum and hot air roasting.
Drum Roasting: Drum type roasting machines roast the coffee beans as they tumble in a rotating drum that is typically heated by gas or wood. When the desired roast is achieved, the beans are poured into a cooling hopper to keep them from overcooking. There are three main parts in a traditional drum-roasting machine: a heat generator; a vessel, where coffee is continuously agitated by rotation of the vessel or by forced heated air; and a cooler, where the coffee temperature is reduced.
Most green coffee is roasted at approximately 400 degrees F. The roasting process causes the coffee beans to swell and double in size while reducing the weight. Once the beans have left the roasting machines they must be cooled immediately to prevent auto combustion from modifying the proper grade of toasting. There are three ways of cooling roasted beans.
- Water-cooling: a shower of water chills the hot roasted beans. Since coffee absorbs water easily this process increases the specific weight considerably.
- Cooling in normal air.
- Cooling in forced air.
A light roasted coffee bean may range in color from cinnamon to a light chocolate. Lighter roasts are generally not used for espresso since they produce a sharper, more acidic taste. Darker roasts have a fuller flavor approaching a bittersweet tang. As a roast darkens, caffeine and acidity decrease proportionately. Dark roasts can range in color from medium-chocolate brown with a satin-like luster, to a black bean with an oily appearance. The darker a roast, the more you will taste the char, rather than the flavor of the bean. As a result, an extremely dark roast will tend to have a smoky flavor and are better suited for brewed coffees rather than espressos. The amount of oil drawn to the surface of the beans increases in proportion to the length of roasting time.
Beans can roast at home by using an ordinary frying pan. It is important to stir often or the beans will burn. A hot-air popcorn popper may also be used. The beans temperature is just right for roasting coffee and the motion of the air will keep the beans moving quickly so they do not scorch. At first, the beans will be too heavy for the hot air to move them. The beans must be stirred until they start moving. After roasting, coffee does not keep its aroma for long. It is best not to roast or buy coffee exceeding one needs. It is advisable to keep it in jars with well fitted lids or in the freezer if certain guidelines are followed.
- A single coffee bean will generally not possess the complexity necessary for great espresso.
- Many espresso blends will contain 3 to 7 different types of beans.
- Arguments still exist among roasters as to which should occur first, the roasting or blending.
- To release aroma and flavor, coffee has to be roasted.
- Well-roasted coffee should be brown, of varying degrees of darkness, but never black.
- Specialty coffees are generally roasted in small batches. The two most common roasting methods are drum and hot roasting.
- The roasting process causes the beans to swell and increase in size by over 50%, while at the same time reducing their weight by about 20%.
- As the roast darkens, caffeine and acidity decrease.
- The amount of oil drawn to the surface of the beans increases with the length of the roast.