Cocoa and Coffee Processing

Prof. Samuel Sefa-Dedeh

Department of Food Process Engineering

Introduction

In 1720 Linne bestowed the name Theobroma cacao on the tree known in Mexico as quacahautl or caucautl.

Theobroma refers to 'Greek for food of the gods')

One of the products derived from cocoa is chocolate. The word derives from chocolatl, the Mexican name of the beverage.

Cocoa was prized for their food value and employed as a medium of exchange.

An important crop in Ghana agriculture and economy

Botanical Classification

All the members of the genus Theobroma are woody plants

Subgroup Buttneriasceae of the order Sterculiaceae

Family: STERCULIACEAE Genus: Theobroma Species: Cacao Two main Sub-species

- Cacao Criollo - Spaerocarpum (Forastero

Criollo

There are four types of Criollo

- Columbian Criollo

- Mexican Criollo

- Nicaraguan Criollo

- Pentagona

These have warty fruits, white and faintly purple seeds

Forastero Three main types

Forastero superior Angoleta

Cundeamor

Forastero Inferior Amelonado

Calbacillo

Forastero Amazonica

These have smooth fruits and deep purple seeds

Amelonado and Forastero Amazonico are the most commonly cultivated.

Cocoa Hybrids

This is a cross between Criollo and Forastero.

They are referred to as Trinitario.

Commercially Criollo and Trinitario types are classified as 'choice' from their quality of flavour.

Harvesting

Ideal harvesting time is one month after the pods are fully grown.

Uniform ripeness is an important index.

Harvesting involves cutting the fruit from the tree.

This usually piled on the ground in the farm.

The pods are cut open and the beans withdrawn either by hand or a wooden spoon

Design challenge: This is a manual operation

Harvested Cocoa Pods

Engineering Design Opportunities for Improved harvesting handling and pod opening

Harvesting rod-knife cutting mechanism

Assembling of pods

Pod breaking to release fresh beans

Fermentation

This is the first stage in the preparation of cocoa beans for the market.

The objective is to prepare a stable product with the desired flavour and aroma desirable for the manufacture of chocolate.

The main changes taking place during fermentation are: Breakdown and removal of pulp Death of bean Release of enzymes to reduce astringency Alteration of texture of seed coat Colour development

Methods of fermentation

Heap Method. This is predominant in Ghana.

The fresh beans are heaped on and covered with plantain leaves.

The heat generated cause the temperature to rise to about 50C

To ensure uniform heating and aeration, uncover and mix 2 and 4 days

Sweat boxes Use a series of perforated boxes constructed without

nails, because iron discolours the beans

Results of fermentation

Well fermented beans are plump, insufficiently fermented beans are flat

Color changes

Interior of white beans become light cinnamon, purple beans become chocolate brown

Drying

Simple sun drying is the preferred method in Ghana.

The fermented beans are spread on raised platforms on raffia mats.

This yields a better flavour than artificially dried beans.

This concludes the curing process.

Engineering Design Opportunities in Cocoa Fermentation and Drying

This is a natural fermentation system. The required conditions are created through regular aeration.

Consider bulk fermentation with a mixing system

Understand the critical drying process parameters in the indigenous sun drying

Mimick the traditional drying process (rate of moisture loss, rate of heating, mixing and aeration)

Cocoa processing-Introduction

Dried beans are cleaned, roasted and shelled.

Kernels are ground to give cocoa mass or chocolate liquor

Cocoa powder: obtained by pulverising the cake after cocoa butter (fat) is removed from the liquor

Chocolate: made by mixing chocolate liquor with sugar, cocoa butter and subjecting refining processes

Cleaning and Grading

Sifting, brushing and ventilating

Sorting into large, medium and small

Large beans are the best for processing cocoa and chocolate

Roasting

Purpose is to develop flavour and aroma,

render the cotyledon plastic for easy grinding.

Loosen seed coat to facilitate easy removal

Roasting Temperature 100-130C Criollo is lower 90-11OC

Forastero requires higher

Period of roasting 15 minutes to two hours

Continuous or batch operation

Roasting and Cooling

Batch roasting Rotating drum

Direct heating or passing blast of hot air through beans

Continuous roasting Drum type. Horizontal drum through which hot air is

passed or the tower type, in which the beans fall down a baffled tower with hot air

Beans discharged on to sieve and cooled by blowing air through perforation in sieve

Breaking and Winnowing

Shell is removed as thoroughly as possible because it impairs flavour and difficult to grind.

Brittle-roasted beans are cracked between toothed rollers and the fragments passed through a series of sieves.

Each sieve fraction meets a countercurrent of air the velocity of which is adjusted to effect the separation of shell and nib in the fraction.

Winnowing to separate nibs from shell

Grinding

This transforms the nibs to cocoa liquor

Different types of grinders are available.

Stones, steel rolls, discs or a combination

Manufacture of and Cocoa Butter and Cocoa Powder

To produce cocoa powder .. A percentage of cocoa

butter must be extracted by pressing from cocoa liquor. When use for the manufacture of cocoa powder, the

liquor is generally treated with alkali to improve the colour and develop the flavour.

The process originated from Holland and is referred to as the 'Dutch process'. It results in the production of alkalised cocoa. Commercially this is known as 'soluble cocoa', because the particles remain in suspension after preparation of beverage.

Alkali may be introduced prior to roasting or at the nib stage but more economical to mix with cocoa liquor.

Manufacture of and Cocoa Butter and

Cocoa Powder Contd

Pressing Production of cocoa butter requires the

pressing cocoa liquor leaving a cake containing only 10% fat or less

Use hydraulic press exerting a pressure of 300 to 600 kg per square cm

Calculation of amount of fat to be expressed

F = 100(T -t) 100-t

F = fat which must be expressed

T = Fat content of the cocoa liquor

t = required fat content of the cocoa powder

Cocoa powder

From the press, cocoa cake is very hard and must be broken up.

It is first reduced to lumps about the size of beans before reaching the pulveriser.

This involves the use of a disintegrator or stone mill. Temperature control between 2S and 30C by passing

cold air below the pulveriser to prevent the liquefaction of the fat. Otherwise the colour of the cocoa powder will deteriorate and it will appear dull and lustress.

Flavouring may be added-vanillin, cinnamon, almond, malted barley, groung hops to produce beverage.

Chocolate Manufacture

The operations include:

Mixing

Refining

Conching

Tempering

Cooling

Mixing

Cocoa mass and very fine sugar are weighed and delivered into a melangeur or kneading machine.

The amount of cocoa butter to be added to obtain chocolate mass can be calculated from:

x = F.C. + (100 - S - C)

x = The required fat content of the chocolate mass

F = The fat content of the cocoa liquor used

C = The amount of cocoa liquor in the chocolate mass

S = The amount of sucrose in the chocolate mass required

Example on mixing

The chocolate mass with 35% cocoa fat and 60% sucrose is to be manufactured. The cocoa liquor contains 55% cocoa fat. How much cocoa butter must be added?

35 = 0.55xC + (100 - 60 - C) C + 11.11kg The quantity of cocoa butter present in cocoa

liquor is given: (11.11) x (0.55) = 6.11 Therefore 35 - 6.11 = 28.89 kg fat/100kg

chocolate mass must be added.

Mixing cont'd

Flavour and lecithin may also be added

If milk chocolate is being manufactured the milk is introduced at this stage.

This is in the form of milk powder or block condensed milk.

If liquid condensed or fresh milk then need preliminary processing to eliminate most of the water.

Refining

Refining rolls are used to reduce the size of coarse particles in the mass by passing through the rollers.

Through efficient refining the dimensions of the sugar particles are reduced to between 30 and 25 microns or smaller

Conching

This is a process designed to improve the flavour and texture of chocolate.

Conching consists of subjecting the refined chocolate mass to intensive stirring at high temperature (85C) for varying lengths of time (1- 7 days)

During the process, cocoa butter is added to bring the chocolate mass to a suitable working consistency. Lecithin and volatile flavours may be made

Conching Cont'd

It is postulated that the following physical and chemical changes occur during conching.

- separation of the agglomerates into fine particles

- Emulsification of the particles in the fat

- Removal of moisture, air and acid materials

- Increased fluidity

- Rounding off the corners of the larger sugar

crystals to give greater smoothness

Conching cont'd

Several types of conching equipment are available

The equipment has a shell-like appearance (concha or shell in Spanish)

The equipment is designed to combine the processes of mixing, emulsification and aeration and must be capable of sufficient grinding to separate adhering sugar particles and possibly to round off their edges

Tempering

The conched chocolate is stoved in the hot room or in a double-

jacketed container prior to being tempered. The aim of tempering is to condition the chocolate until it is in an

ideal state for deposition into moulds or for coating centres During carefully regulated tempering, crystallization of

about 3% of the total fat takes place In bulk the chocolate is tempered in batches in a water

jacketed kettle equipped with scrapers, stirrers ot by continuous tempering machines which pass the chocolate through the appropriate temperature cycle over water- cooled rollers or down a spiral ribbon space in a water- cooled cylinder

Tempering Cont'd

In order to avoid supercooling and to check the tendency of the grains to coarsen, it is usual to cool the chocolate to below the desired temperature and then to bring it back by cautious reheating

Temperature of tempered chocolate will generally be in the range 86 to 92F

Cooling

Highly polished metal moulds are warmed up to the same

temperature as the tempered chocolate which they are to receive.

They pass beneath the depositing tank and an exact weight of chocolate is forced into each tin.

The filled tins proceed to cooling tunnels, subjected to mechanical shaking for the liberation of air bubbles

If it is chocolate-centered goods being manufactured, the centres (which can be nuts, fruits, caramel etc.) are passed under an enrobing device in which each centre receives a baptism of chocolate from the enrober tank.