Ecology

• Ecology
• Physical properties of coffee

ECOLOGY

Coffee is a tropical plant which grows between the latitudes of 25 degrees North and 25 degrees South but requires very specific environmental conditions for commercial cultivation. Temperature, rainfall, sunlight, wind and soils are all important, but requirements vary according to the varieties grown.

Ideal average temperatures range between 15 to 24ºC for Arabica coffee and 24 to 30ºC for Robusta, which can flourish in hotter, drier conditions but does not tolerate temperatures much below 15ºC, as Arabica can for short periods. All coffee is easily damaged by frost, a danger either in southern Brazil or, closer to the Equator, at altitudes around 2000 metres.

In general, coffee needs an annual rainfall of 1500 to 3000 mm, with Arabica needing less than other species. The pattern of rainy and dry periods is important for growth, budding and flowering. Rainfall requirements depend on the retention properties of the soil, atmospheric humidity and cloud cover, as well as cultivation practices. 

Whereas Robusta coffee can be grown between sea-level and about 800 metres, Arabica does best at higher altitudes and is often grown in hilly areas. As altitude relates to temperature, Arabica can be grown at lower levels further from the Equator, until limited by frost. All coffee needs good drainage, but it can grow on soils of different depths, pH and mineral content, given suitable applications of fertilizer.

Wind-breaks are sometimes planted to protect coffee plantations; shade trees, which may be economic crops such as bananas, are a common feature and mimic the natural habitat of coffee.

Standard references
Clifford, M.N. and Willson, K.C. (Editors) - Coffee; botany, biochemistry and production of beans and beverage. London, Croom Helm, 1985.
Wrigley, G. - Coffee. London, Longman, 1988.

PHYSICAL PROPERTIES OF COFFEE

All food products possess characteristics which are related to their state, aspect or appearance such as weight, volume, size, shape, colour, solubility, moisture content, texture, etc. Coffee is no exception. From the tree to the cup, the various physical characteristics of coffee in its different forms play an important part in the way it is treated and in the design of processing equipment. Coffee is harvested when its red colour indicates that the appropriate maturity has been reached. Flotation or winnowing is used to physically separate defective cherries on the basis of density and to remove twigs and stones. Size, shape and colour are used to grade beans after they have been dried to an even moisture content for storage. Because coffee beans have a porous, spongy texture, they can easily be contaminated by microscopic fungi, giving rise to off-flavours, or pick up strong odours, and deteriorate rapidly if allowed to become too moist.

Coffee is a natural product and therefore variable, but some typical physical properties of coffee are listed below:

Weight yields

Wet process: 250 kilos fresh cherry --> 100 kilos wet pergamino --> 55 kilos dry pergamino --> 45 kilos dry polished coffee;

Dry process: 250 kilos fresh cherry --> 90 kilos dry cherry --> 45 kilos dry polished coffee;

Roasting causes on average a 16 percent loss in weight and an increase in bean volume of 50 to 80 percent.

Moisture

Fresh cherry: 50 percent
Green bean: 12.5 percent
Roast coffee: below 7 percent (depending on humidity)
Soluble powder: below 4 percent

Standard references
Sivetz, M. and Desrosier, N.W. - Coffee technology.Westport, Connecticut, AVI Publishing Company, 1979.
Clarke, R. J. and Macrae, R. (Editors) - Coffee Vol. 1 Chemistry (1985) and Vol. 2 - Technology (1987). London, Elsevier Applied Science Publishers.