|
Coffee is the world's most popular beverage after water, with over 400 billion cups consumed annually.
Coffee is also grown in Hawaii, India and in Southeast Asia.
Geographically, coffee grows between the tropics of cancer and tropic of capricorn. Outside this area there is opportunity for frost which damages the coffee plant. Hilly mountainous areas near the equator are more likely to be exposed to frost.The main growing areas of coffee are Latin America, Africa, Caribbean Islands , the Arabian Peninsula, and Indonesia . In chosing a location for the growing of coffee the chief considerations are
(1) Altitude
(2) Soil
(3) Climate
(4) Diseases
(5) Economy
The higher the altitude, the better the quality of coffee. The limiting altitude is the frost danger zone. Frost damage turns the leaves of the coffee tree brown, killing them.
Prescence of an adequate supply of essential mineral elements,temperature, moisture, friability, ph, drainage, degree and orientation of slope are important. The soil must be porous to allow for easy drainage after heavy rains, organic enough to hold moisture between rains, wet and soft so that the feeder roots and deeper water tapping roots gowth is possible. Most of the worlds coffee is grown on volcanic soils in areas near extinct and live volcanoes, where soils are rich in minerals and slightly acidic (PH 4.5-5.0) Potassium and iron are some of the minerals that are important in healthy coffee shrubs
The best coffee climate is determined by mean temperatures diurnal as well as seasonal variations, the possiblity of frost, rainfall and its distribution throught the year,ability to irrigate, sunshine and cloud pattern.
One two or three seeds may occur in a single ripe coffee fruit, cold cherries or grapes. Seed maturity occurs 6-9 mths after blooming, which is triggered by rainfall. The fruit matures more slowly under shade
Today several hundred million people in the world drink coffee, Americans alone drink about 430 million cups of coffee a day. The commercially important species of coffee both of which originated in tropical Africa are now grown in some 80 countries in the four continents of which 50 export their crop. Judged by total value coffee is one of the leading commodities in international trade. Many African countries inluding Uganda, Burundi, Rwanda and Ethiopia have coffee as their major source of foreign exchange.
Coffee is cultivated from a plant called Caffea Arabica if its of the arabica species and caffea canephora from the Robusta species. It was discovered as early as the 15 th century and is indigenous to Ethiopia. The coffee tree belongs to a family called Rubiaceae. The shrub is a perennial, evergreen dicotyloden and can reach a height of 10 meter, however its usually prunned to 3 meters to facilitate harvesting and provide the right amount of shade.
The first flowers produced by the coffee plant are evident in the first three to four years and they have the following features:-
(1) They are creamy white
(2) Sweetly scented
(3) Appear in clusters
The Robusta coffee plant has to be cross-pollinated while the Arabica is self pollinated. The ovaries of the flower will develop into drupe(small pulpy fruit), the cherries are first green then ripen to a deep red colour.
Within the coffee berries there are beans which have seeds ( dicotylodens), each fruit having two seeds. The bean is covered by a closely fitting legumen called the silver skin, and then surounded by a partly loose skin called parchment, the later of which is enclosed in a mucilaginous pulp. If one of the beans fails to develop the bean is said to be pea-berry.
Coffee is grown in the tropical countries where the largest consumers are found. The world largest produce is south America.
The main coffee growing areas in Kenya are Central province, Eastern provine, Nyanza province and Western province.
The methods of processing coffee determine its quality. The two main methods or processing are:
(i) Dry Processing
(ii) Wet Processing
Wet Processing:
This method is mainly used on Arabica coffee and is extensively used in Kenya. It produces superior quality coffee. Only ripe berries are picked . The berries are soaked in water and fed into a pulper, a machine that removes the outer skin of the berries. The pulp (inside of the berry) is disposed of as waste leaving just the parchment (coffee seed). The pulp is a possible environmental pollutant if it is allowed to get into water systems. Click here to view the ways in which the pulp is recycled to reduce harm to the environment.
- Pulp contains 14.4% sugar content and gives ethanol.
-Coffee pulp is used to produce vinegar.
-Coffee pulp is about 10% protein and has been used in animal feed.
-Coffee pulp is also used as mulch or compost in the garden.
-It may also be sun dried on a terrace and used as fuel.
Dry Processing:
In this process, the coffee berries are allowed to remain on the tree past the fully ripe stage. After harvesting they are dried to about 12% moisture after which all the outer layers are removed by hulling. The coffee produced from this is of a lower quality compared to that produced by the wet method.
Coffee Processing( Wet Method ):
The wet method of processing has got various stages:-
Reception of Buni
The berries are quiclky transported to thier processing area to avoid heating the mass which would otherwise result in discoloured bean. The coffee is loaded into a a receiving tank which is filled with water and has an over flow weir with a device allowing floaters to be discharged from the rest, before coffee is processed it is manually sorted for under ripes, over ripes, leaves and twigs the recieving tank is eqipped with a siphon which will transport the heavier berries to the pulper by gravity
Pulpin Stage:
The outer skin is removed and this is done mechanically under running water leaving behind parchement and the mucilage. The mucilage acts as a lubricant where it prevents mechanical damage to the bean, Water also acts as a lubricant to the squeezing , helps to carry and clean the cherries. The pulping action entails squeezing compression and tearing. If cherries are unpulped they then pass through a narrow adjustment and repulped. Coffee pulping can be done by drum pulpers, disc pulpers and hand pulpers, where disc pulpers are commonly used in Kenya. The ripe fruit is squeezed in a pulping machine the later which removes most of thes oft outer pulp leaving a slipery exposed layer of mucilage. the disc pulper has
a rotating metal disc with a roughened surface and stationary metal or nylon board with an adjustable distance between them. cherries are pressed between the two surfaces to effect pulping.
Pregrading of parchement:
Freshly pulped parchment is graded on basis of weight and size by shaking sieves and water at a constant flow. pregrading sorts out unpulped cherries and skin and directs them to a repulper; it also seperates parchement into categories of quality
1 parchement 1
2 parchment 11
3 lights
lights are furthur processed seperatly with a lot of care. The grading is regulated by velocity of water flow. Heavy parchment sinks rapidly and passess through the holes in the shaking sieves according to size. Lighhts don't sink while unpulped and large beans sink but do not pass through the grading screens and are taken to the repasser pulper.
Fermentation
This is an enzymatic process which degrades the thick mucilage layer, which covers the pulped parchment. The mucilage is degraded into a simple nonsticky substances which can easily be washed of with water. Removal of mucilage is very important because it is sticky and inhibits drying, attracts dust, makes handling difficult and is a good subtrate for spoilage micro-organisims. Mucilage generally contains the following components
1) Pectins-33%
2) Reducing sugars-30%
3) Non reducing sugars-20%
4) Fibres and ash-17%
The natural enzymes in the mucilage are initially involved in the hydrosis. Later, yeasts and bacteria from the tank wall, the water used and the outer surface of the fruit skins begin to grow and form pectic enzymes which continue the process.
The length of the fermentation time diffes mainly as a function of climatic conditions and the condition of the crop. In regions of low altitudes, where robusta thrives fermentation time is very short, whereas at high altitudes fermentation generally takes some 48 hrs.
In the course of fermentation, the bacteria remains dormant during the lag-phase, there is an increase in bacterial activity where sugars are broken down. Consequently the bacteria multiplies so that
the rate of substrate degradation increases. The shortage of substrate with continous consumption and build up of catabolic products reduces bacteria growth.
Due to bacterial degradation on sugars , organic acids are produced. The acids then reduce the ph of the fermenting medium from 5.6 -less than 4.0 thus increasing yeast activity. When yeast degrades the sugars alchol is formed and is characterised by a strong odour. Fermentation is complete when the parchment feels gritty and is no longer sticky
Biochemically, lactic acid (lactose) and carbohdrates, are fermented with the production of propionic acid, acetic acid, carbon-dioxide and alcohol.
Washing:
After fermentation the parchmenrt is washed about 4 times to remove all traces of mucilage together with the breakdown products of fermentation of the mucilage, any remaining mucilage cna ferment giving the final product an undesirable flavour. During washing the beans are stirred with wooden shovels to remove all residue care is taken not to bruise and discolour the beans.
Soaking:
After washing, the coffee is soaked under water overnight. This under water soaking enhances final-coffee quality through modification of liqour characteristics. It also improves the appearance of the raw bean. After soaking overnight, the beans are then rinsed with clean water.
Onion Flavor:
This is a quality problem associated with faulty fermentation, it is an off flavour which deteriorates the quality of coffee.
The actual cause of onion flavor is has not been confirmed although the following sources have been suggested to cause onion flavor.
(1) Raw bean colour was suggested to be highly correlated with liqour flavour where beans with tints of blue are of high qualitry followed by grey and green
(2) Rayner(may 1950) concluded that onion flavouris most probably the result of processing susceptible coffee and to a lesser degree the result of using to much water especially before and during fermentation. Later Mccoly (feb 1950) suggested that delyed skin drying is possibly responsible.
It was also suggested that onion flavour reports on liqour was related to the occurence of propionic acid in the corresponding fermentation, and this depended on the amount, where high concentration of pioponic acid earned 'foul with onion flavour" while low concentrations were ascribed 'suspicion onion flavour" and on some occasions had no onion flavour dectectable by the liqouring department.
There as some factors that promote the production of propionic acid
(1) Over fermentation(over 72 hours)
(2) PH-proponic acid has not been detected in fermentationm with a ph of less than 4.3
(3) Suger concentration where very low initial sugar concentration is favorable for production of onion flavour.
(4) Pro-longed pre-washing; usage of large volumes of water promotes onion flavour developmnent
(5) Coffee maturity-presumably due to it's low initial sugar content, the under ripe cherry give rise to onion flavour than more mature cherry.
(6) Presence of offending microorganisims e.g yeasts moulds and bacteria which are introduced into the fermenation tank by means of water and the cherry can cause onion flavour.
Drying:
Drying is the process of reducing moisture content of a product so that it can be furthur procesed or stored for long periods without deterioration
Little information is available on the basic drying characteristics of the coffee-bean. The limited work undertaken to date indicate that, drying of coffee beans is greatly influenced by temperature, and sample properties which are thought to include:-
(i) Altitude at which coffee was grown
(ii) Degree of ripness.
(iii) Cultutival practices
(iV) Time of storage prior to drying
(V) Variety of coffee bean.
Two disticinct drying phases of coffee bean are known to exsist, the constant and falling rate stages. Depending on the temperature employed, the length of either phase invesely other. For coffee-bean to dry at a fast rate, the constant rate drying phase has to be made as long as possible. Since it is faster than the falling rate . It is possible to dry coffee-bean at a constant rate to 10-15 % moisture content, which is considered necessary for its stability against microbial activity. It is then possible to achieve this through a constant rate drying period with air temperature set between 75 degrees C and 150 degrees C. Use of air temperatures higher than 150 degrees c shortens the constant rate drying period, thereby lengthening the retention time and possibly winning the nutritive value of the dry bean. Due to the high moisture content and other inherent properties of coffee-bean it is normally rather expensive to lower its moisture content down to between 10% and 15% by drying alone because of the high temperatures required for fast drying. Use of low dryng temperature would make the drying period so long that the bean would have degenerated due to the length time
From experiments using various driers and drying systems, sun drying has been identified to be the most common and viable system in terms of technical and economical cosiderations despite the long weather dependent drying time which might lead to microbial contamination.
Freshly pulped fermented and washed parchment coffee has a moisture content of about 55 % which has to be reduced by drying to 10.5 % which is the safe level for hulling storage and roasting
In Kenya parchemnt is normally dried in the sun scince sunlight has a definite and proven quality benefit, during the soft black stage (30-20 %mc) of parchement, drying has been recommended in Kenya for at least 48 hrs.
Drying coffee is critical and should be done carefully. Under drying causes rapid fading of bean colour, while overdrying leads to unnecessary weight lose and quality degradation. Certain chemical and physical changes occur to the bean during drying and affect quality; however these changes (chemical and physical) need to be investigated
Distinct stages of parchment drying.
Skin Drying Stage:
This is the first drying stage, which removes surface moisture and moisture betweeen the bean and parchment from 55 % to 45 % mc. The drying is done quickly and rapidly after final washing to remove all the surface moisture that may cause bacterial growth and therfore taints. It is competed on the day of final washing to avoid rotting, gernmination , moulding and decay from occuring. The parchment is spread thinly on wire mesh tables and is turned frequently to encourage rapid evaporation and to make sure the parchment is fully exposed to the sun. A lot of labour is required and hand sorting is best done at this stage.
White stage drying(45-30mc)
At this stage the beans are whitish and soft but towards the end of the stage fatty acids cafestol and kahweol are formed in the bean and are of quality signicance. They have been sugeested to play part in the formation of the desirable bluish and greyish colours of raw coffee.
Coffee should not be strongly irradicatred at this stage so as to avoid cracking of parchment. The cafestol and kahweol esters formed at this stage are sensitive to irradition and can break down into complex products no longer capable of giving rise to the desirable colours. This stage requires slow drying and can be dried under shade during the hottest hours of the day, thus the coffee is usually covered on the drying tables around midday in hot weather.
Soft Black stage drying(30-20% M.C.)
This is the stage when the final colour of the bean is formed as the moisture drops from 30-20 %. Sunlight is very essential scince formation of the raw bean colours is photosensitive at this moisture level. It is therefore strongly recomended in Kenya that the coffee should be fully exposed to sunlight for a period of at least 2 days to improve the colour
Black Stage Drying
1 Medium Black Stage:
The bean is fairly hard and black all over . Drying can be done rapidly without aany effect on quality. Sun
or machines can be used for the drying or caoffee can be heaped to one inch thickness on tables quite safely.
In-case of congestion the coffee can be tempararily in ventilated storage bins and be taken outr later for final
drying.
II Hard- Black stage:
The coffee is now fully hard and can be dried rapidly without effects on quality
Conditioning (11.0-10.5 mc):
This is the final stage of drying and is usually done in ventilated stores or bins. Dry air is blown by fans to
even out the moisture content of the parchment at 10.5%, the parchment is fully dry and safe for storage. At this
MC and 60% relative humidity, the c
Coffee Bean- Defects:
(i) Black-bean:
The surface and the interior of the bean is wholly or partly dark. The defect may occur on faulty drying or
storage.
(ii) Stinker bean:
This is a brownish yellow bean whose embryo has been destroyed. It occurs due to fungal action on
pro-longed fermentation periods or over-heating during early stages of drying.
(iii) Insect damaged bean:
The bean has holes and tunnels caused by berry borers. The damage may occur in the field or in storage.
(iv) Amber bean:
The bean has a yellowish appearance. The defect develops in areas with very low iron content in the soil.
(v) Green water damaged:
Beans have a dark sea-weed colour with brown and partly black patches as well. They (beans) appear
shrunken and small in size. The defect is caused when beans are exposed to moisture while in the drying process or
when skin drying stage is prolonged. This defect is the initial stage of black bean development.
(vi) Woody coffee (aged coffee):
Beans are brown in colour with a whitish coating on the surface. The edges of the beans have a lighter
brown colour. The defect occurs when hulled coffee is stored for too long at uncontrolled conditions of
temperature and humidity.
(vii)Faded and mouldy coffee:
Beans have a whitish, pale appearance due to mould growth on the surface. Some of the beans are
ragged and dark at the tip. The defects occurs when coffee is uinder dried (above 11 % M.C.) and stored in humid
conditions.
(viii) Foxy beans:
Beans have a brownish silverskin. The defect occurs as a result of picking over-ripe cherries
Storage of Dried Coffee:
The dried coffee should not be stored in an enviroment where it can pick up or lose moisture causing
spoilage. In high relative humidities and warm temperatures, coffee beans will absorb moisture and mould growth
can occur. Beans may also be bleached out in colour and loose some desirable flavour properties.
Storage of coffee as parchment results in much less deterioration than when stored as clean coffee. Thje
parchement husk and silveskin coating are barriers to ambient influences that may damage the seed.
Packaging Method for roasted and ground coffee:
(1) Filling the coffee into cans which are either evacuated and sealed under vacuum or evacuated, flushed
with inert gas and then sealed.
(2) Packaging in flexible laminated or metallised pouches , with inert gas flushing, or in flexible vacuum
packages (brick-packs) both of which usually require a preliminary ‘ degassing” treatment to remove from the
ground coffee as much as possible the carbon dioxide which would otherwise would be released from it to produce
a “balloned” appearance
coffee suffers no quality losses.
1.2.4 Chemical Compostion of green coffee
The chemical composition of green coffee depends on the species and variety in question. It also depends on
other factors, like
(1) Agricultural practices
(2) Degree of maturation
(3) Storage conditions
(4) During roasting where the more labile componenents are degraded and the more reactive compounds interact to
form complex products
(5) On extraction to form coffee brew, the more water soluble components are preferentially extracted.
Coffee Roasting
This is the process of exposing the green coffee beans to a warming process that is sufficently fast enough to
drive off the free and bound moisture of the bean and the dried bean is heated to more than 400 degress
farenheit(200 c). At about this temperature pyrokysis or thermal decomposition and chemical change occurs within
the bean.
In a fraction of a minute, exothermic (heat liberating), chemical reaction occurs. The bean temperature rises
to 200c to 210c with an accompanying dry bean weight loss, rising from 4 to 6 %. The higher the % loss, the
darker the roast colour. The brown colour development of the bean occurs during this periond with the
simultaneous revelation of the chaff at the bean crevice
Termination of the roasting process
1 At the desired flavour which is equivalent to the desired degree of chemical pyrolysis and concitant weight
loss.
2 It is guided by the darkness of colour developed at the point of roasting
3 By the temperature of the beans as it is under automatic temperature control system on batck roasters.
Roast weight- Losses at two rates:
(A) 1st rate:
This is a slow rate (low slope) and it is due to the evaporation of water from the bean.
(B) 2nd Rate (steep Slope)
This is the rate where pyrolysis occur. As the rate of water loss falls of the rate at which carbon-dioxide gas
is evolved rises rapidly. This point of transition occurs at the beginning of prolysis at about 185 c or at about the
time of 10% weight loss of the green bean.
During roasting the actual time temperature and colour affects will vary with
(a) Method of roasting.
(b) Time cycle.
(c) Type of bean.
(b) Critical moisture
(e) Rate of heat transfer.
Some of the pyrolysis chemical products are
(1) Carbon dioxide
(2) Aldehydes
(3) Ketones
(4) Ethers
(5) Acetic acid
(6) Methanol
(7) Mist
(8) vegetable oil
(9) Glycerol-which are voltaile from the beans
When the bean roasting time exceeds half hour, the coffee beans tend to develop more of a flat baked
flavour than a rich aromatic flavour.
Roasting is accompanied by popping sounds and oily smoke which is mostly water vapour with a blue
colour.
As soon as the bean colour is reached the beans must be removed from the heated gasses and promptly
cooled by ambient air and or a water spray. Most of the sprayed water evaporates off cooling the beans with
hardly any water being absorbed by the beans, cooling the roasted beans stops the prolysis reactions.
Results of Bean Roasting
(I) About 2 % carbon dioxide gas is produced within the roast and the cell structure disrupts.
(II) Sugars and starches are converted to homolgus acids e.g aceticpropionic and butyric acids as well as homologus aldehdes like acetic-propyl.
(III) Water soluble proteins become denatured.
(IV) Many protiens react with sugars to form brown products and caramel.
(V) little %age of the coffee oils break down to yield fatty acids and glycerol.
(VI) The softening of the coffee- beans cellulose structure, with heat and pressure of pyrolysis products, causes the roasted bean to swell to twice its bean volume.
©2002, Batian Peak Coffee
|
