Processing of cocoa beans

Transcription

1 Paper No. 09 Paper Title: Bakery and Confectionery Technology Module No. 29 Module Title: General aspects of cocoa bean processing: cocoa mass, cocoa butter and cocoa powder Introduction: Cocoa is a cash crop grown throughout the humid tropics. It is mainly consumed as chocolate confectionery, chocolate coated products (biscuits, ice creams), or in other food products containing cocoa powder, including beverages, cakes, snacks, etc. The cocoa or cacao tree (Theobroma cocoa L.) is a native of Amazon basin and other tropical areas of south & central America, although most commercial cocoa is produced in West African countries, with Ivory Coast counting for the 37% of the worldwide production and Ghana for the 20%. Most of the world's cocoa is grown in a narrow belt 10 degrees either side of the Equator because cocoa trees grow well in humid tropical climates with regular rains and a short dry season. The trees need even temperatures between o C, with a fairly constant rainfall of mm per year. The cocoa tree is relatively small, 12-15m in height. Trees start bearing pods after 2-3 years. The cocoa tree bears two harvests of cocoa pods per year: a small harvest at the beginning of the rainy season, a big harvest at the end of the rainy season. Around 20cm in length and 500gms in weight, the pods ripen to a rich, golden-orange colour. Within each pod there are purple, 2 cm long cocoa beans covered in a sweet white pulp. The beans consist of an outer shell or testa surrounding two cotyledons (Nibs) and a small germ. There are about 20 known varieties of the cacao tree and hundreds of hybrids. For chocolate making four types of cacao trees - Criollo, Forastero, Trinitario and Nacional are cultivated. The Forastero cacao constitutes approximately 80% of world production of cacao. It is used as a base to be blended with superior types of cacao such as Criollo, Trinitario and Nacional and considered as bulk bean. The other three are considered as flavor beans. The Trinitario is a crossbreed between the Forastero and Criollo It has its aroma from Criollo and its resistance to disease, productivity from Forastero. The Nacional is prone to disease and difficult to grow, but has an excellent aroma.

2 Processing of cocoa beans The pods are split open by hand and the cocoa beans along with the adhering pulp are removed. The cocoa bean then undergoes several processing technique for the production of cocoa mass, cocoa butter and cocoa powder. As per the PFA Standard, the cocoabean, coconib, cocomass, cocoa press cakes and cocoa powder (Fine/Dust) may be referred as 'Cocoa solids'. The various techniques for processing of cocoa bean are as follows: 1) Fermentation 2) Drying 3) Cleaning of nib 4) Roasting 5) Winnowing (cracking and fanning) 6) Grinding of nib to produce cocoa mass (liquor) 7) Expelling of cocoa butter from the liquor 8) Grinding of cocoa cake to cocoa powder 1) Fermentation After the pods are cut from the tree, beans (with adhering pulp) are removed and fermented by any one of the four different methods- heap, platform, baskets, boxes. The platform and heap method of fermentation or sweating is used traditionally by farmers in West African countries however, at present most of the commercial application involves box method of fermentation. The wet cocoa beans are placed in a wooden fermentation box, which has a slated floor, and covered with banana leaves. The slated floor of the box allows for the drainage of liquids during the process. The mass of fermenting cocoa beans is "turned" every two days. "Turning" the fermenting cocoa beans allows the dissipation of heat and also aids in the aeration of the mass. The entire fermentation process is completed in 6-8 days depending on weather conditions. The fermentation process develops the unique flavor and aroma of cocoa beans. The chemical changes occur during fermentation both in pulp and cotyledon (nib). The pulp is composed of approximately 85% water and 11% sugar with small amounts of citric acid, pentosans and proteins. During the fermentation process- Sugars in pulp break down to ethanol and lactic acid and temperature rises to about 45 C during first two days of fermentation.

3 During the remaining period of fermentation temperature remains between C. The ph rises to 5.0. Turning of heap aids in oxidization of alcohol to acetic acid. The cotyledons gain moisture during fermentation and the texture changes from cheesy coherent mass to a fissured structure. The colour of the bean also changes from slaty gray to purple, purple brown and finally to dark brown. The Forastero type beans achieve rich dark brown colour whereas a light brown colour is developed in Criollo types beans. The germination time, temperature and presence of carbon dioxide are the factors affecting the flavour and colour of beans. Germination must take place during the first stages of fermentation followed by death of beans in hours. After germination temperature must be maintained at around 50 C for several days. The carbon dioxide surrounding the beans must be removed by turning. 2) Drying The main objective of drying is to reduce the moisture content of the fermented cocoa beans to a level of 6-8% which is safe for storage. Also during drying, the fermentation process is completed. Sun drying and artificial drying are the two methods used, with sun drying being the preferred method. Drying should be gradual and the fermented cocoa beans should be turned regularly to ensure that the drying is uniform. On the first two days of drying, the cocoa beans should not be exposed to a full day of sunlight. In good weather, drying should be completed in 7 days ( sun hours), while artificial drying takes less time. Fermented and dried cocoa beans must be stored in suitable environment so that they do not pick up moisture during storage. Traditionally they are stored in kg jute sacks in well aerated rooms. The dried cocoa bean (6.5% moisture) contains 87.1% nib (cotyledon), 12% shell and 0.9% germ of which cocoa bean is the valuable part. 3) Raw bean Cleaning Raw cocoa beans received at manufacturing facility may contain minor amount of surface grit, bag fiber, and small stones. These must be removed for the following reasons:

4 To avoid damage to the machineries in subsequent grinding process. To have good quality roasted beans since the organic contaminants in beans affects characteristic roasted flavor of cocoa beans. The machinery for cleaning consists of a series of operations that uses screens of varying meshes, brushes, air lifts, metal detectors, specific gravity separators and magnetic separators. 4) Roasting Raw cocoa beans are roasted to develop further the true chocolate flavour. During the roasting of fermented and dried beans, the following changes occur: Loss of moisture in the beans: the raw nib and the shell contain 4-5% and 8-10% moisture, respectively which is reduced to 1.5-3% and 4%, respectively. Loosening of the shell Enhanced friability and darkening of colour of the nibs (cotyledon) Maillard reaction or non-enzymatic browning for color and flavor development The time and temperature of roasting and the rate of moisture loss greatly effects these changes. A heat treatment as an alternative to roasting is given in two stage- Low-temperature heating (< 100 C) to dry and loosen the shell only High temperature heating ( C) for roasting effect. Temperature in this stage is chosen depending on the requirement of manufacture (chocolate or cocoa powder/cocoa butter expression) As an alternative to whole bean roasting, some processor prefers roasting of nib. In case of nib roasting, machines used are very much similar to that of bean roasting. The nib roasting improves energy efficiency of roaster (because of smaller size of nib) and nibs are more rapidly and uniformly heated. There are two kinds of roaster available for either bean or nib roasting: Batch type roaster Continuous type roaster 5) Winnowing (cracking and fanning) A shell content of much above 1.5% may seriously affect the quality of nibs. Hence the shell and some of the germ are separated from the rest of the beans by winnowing process. This

5 separation is based on the difference in apparent density of the nib and shell. Winnowing machine takes combined action of sieving and air elutriation. For the winnowing process it is desirable that around 85-90% of the nib pieces should be over 3 mm in size because particles of smaller size may not be separated from the shells in air separation. Some pre-treatments like micronization reduce the amount of fine particles at the cracking stage. This treatment also reduces the transfer of cocoa butter from the nib to the shell. In the micronization treatment the cocoa beans are subjected to radiant heat for sec which causes differential heating and drying of shells and nibs. It results into detachment of the shells from the nib. The cocoa nib thus obtained after winnowing is either ground to produce cocoa liquor (cocoa mass) or subjected to expelling to obtain cocoa cake. 6) Grinding of nib to produce cocoa mass (cocoa liquor) The fat in the cocoa nib (approximately 55%), also termed as cocoa butter, is locked in the cells in solid form. In the grinding process, the cell wall ruptures resulting into release of fat. The frictional and applied heat melts the fat also. The particle size of non-fat constituent is also reduced. It results into the formation of a paste with enhanced fluidity. The following are the main aims of grinding the cocoa nib: To make the cocoa particles small enough (30 microns to 0.5 cm) so that they can be made into chocolate To remove as much fat as possible from the cells within nib (cotyledons) There are many machines for grinding cocoa nib to liquor (cocoa mass): 1) Impact mills 2) Disc Mills 3) Pin or hammer mills 4) Ball or bead mills The cocoa liquor is treated for flavour development and removal of unwanted flavours by using the following methods: Simple heating of thin films Thin film roasting and air scrubbing Thin film roasting with-vacuum

6 7) Expelling of cocoa butter Cocoa butter is obtained by hydraulic pressing of finely ground cocoa liquor (cocoa mass) in a horizontal press. Hot cocoa liquor is fed under pressure into the press, which is then pressed by a steel ram operating at a pressure of about 40-50MPa. The reduction of fat content in cocoa cake is dependent on the time cycle, weight of cocoa butter, and distance of ram travel. To obtain an optimum yield the following points needs to be considered: Optimum temperature of the liquor ( C) Moisture content (0.8 to 1.8 percent) Degree of roast (high roast beans) Homogenizing Particle size (98-99% particles passing through a 200 mesh sieve) Pressure Extruder, expeller or screw presses could also be utilized for the extraction of cocoa butter from winnowed nibs, whole beans and blends of winnowing products consisting of fine nib dusts, small nibs and immature beans. In this, the material is forced into the tapering tube of the press by the rotating screw. In the press the shearing action and increasing pressure on the material forces the fat out through the tube slits. Prior steaming of the material softens it and aids in release of fat in shearing action. The material remained after extracting cocoa butter from the nib is called cocoa press cake. Solvent extraction is also employed for extracting cocoa butter from the cocoa cake which is obtained from expelling of whole beans and blends of winnowing products consisting of shell. For solvent extraction the recommended solvent by PFA Standard is n-hexane (Food Grade). It has also set the maximum tolerance limit of 5.0 ppm for the solvent (n-hexane) in the refined extracted cocoa butter. As per the FSSR Standards, 'cocoa butter' means the fat obtained by expression from the nibs of the beans of Theobroma cocoa L. Press, expeller or refined cocoa butter may be referred as 'cocoa butter'. It shall be free from other oils and fats, mineral oil and added colours. It shall conform to the following standards:

7 Particulars FSSR limit Percentage offree fatty acids (calculated as oleic acid) Not more than 1.5 Iodine value 32 to 42 Melting point C Butyro-refractometer reading at 40 C OR 40.9 to 48.0 Refractive Index at 40 C to Saponification value 188 to 200 8) Grinding of cocoa cake to cocoa powder Cocoa powder is produced by milling the cocoa press cake obtained by hydraulic pressing, extrusion, expeller or screw press and solvent extraction. A cooled pin or hammer mill is used to finely grind cocoa press cake to powder. During grinding, the cocoa butter present in cocoa powder may melt at a temperature above 34 C which may cause the adhesion of the particles and clogging of the machinery. At temperature below 34 C, some of the glyceride fractions of the cocoa butter melt and cause the powder to cake. Hence the cooling and feed rate is adjusted so as to attain a powder temperature of C at the exit of the mill. Cooling is done by using dry air (RH of less than 50-60%) to avoid increase in moisture content of cocoa powder. The cocoa powder has to fulfil the third most important criteria of fineness after flavour and colour. The coarser the particle, the more objectionable sediments will be in milk or water. The fineness of cocoa powder may be determined by the 1) sediment test and the 2) sieving test. Cocoa powder finds several applications in beverages, confectioneries, baked products, ice creams and many more. The cocoa powder shall contain minimum 10% and 20% cocoa butter (on moisture free basis) in low fat and high fat cocoa powder, respectively (FSSR Standards). It may be subjected to treatments during manufacture with alkali and/or magnesium carbonate, bicarbonate, and with tartaric, citric or phosphoric acids. It shall be free from rancidity, dirt, filth, insects and insect fragments or fungus infestations. It shall conform to the following FSSR Standards:

8 Particulars Total ash (on moisture and fat free basis) Ash insoluble in dilute HCI (on moisture and fat free basis) Alkalinity of total ash (on moisture and fat free basis) Cocoa butter in low fat cocoa powder (on moisture free basis) Cocoa butter in high fat cocoa powder (on moisture free basis) PFA limit Not more than 14.0 per cent Not more than 1.0 per cent Not more than 6.0 per cent as K 2 O Not less than 10.0 per cent Not less than 20 per cent Alkalization Alkalization of the beans, liquor, nibs or powder is done to change their color. It is usually done with solutions or suspension of alkali, usually potassium or sodium carbonate. The other alkalis used are sodium or potassium bicarbonate or hydroxide, calcium hydroxide and ammonium carbonate or hydroxide. For powder treatment ammonium compounds are used as excess ammonia can be driven off by heat. Suggested readings Minifie BM (1997). Chocolate, cocoa and confectionery. CBS Publishers and Distributors, New Delhi. Beckett ST (2008). The Science of Chocolate (2 nd Edition). RSC Publication, UK. Talbot G (2009). Science and Technology of enrobed and filled chocolate and confectionary and bakery products. Woodhead Publication, UK.