Elimination of odours in cocoa industry - Bluer Medio Ambiente, S.L.U.

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Elimination of odours in cocoa industry


Origin of cocoa

The cocoa tree, or cocoa, is a perennial plant that yields several crops per year. It receive the scientific name of theobroma cacao L. which means "food of the gods", and comes from Greek language. It began to grow in America, where it already was a basic product in some cultures before the European colonizers arrived. The Aztecs believed that the god Quetzalcoatl had taught the cultivation of this species to their ancestors and, many times, cocoa seeds were used as currency in commercial transactions. Cocoa comes from the tropical regions of Mexico and Central America, although in the sixteenth century it was introduced in Africa, where it is most cultivated today. In America today it is grown mainly in Brazil, Ecuador, Mexico, Colombia, Venezuela and the Dominican Republic.

It reaches an average height of 6 m and has glossy leaves up to 30 cm in length and small pink flowers that are formed in the trunk and in the older branches. Only about thirty of the approximately 6,000 flowers that open during the year form a fruit, which is called “pineapple” or “maraca”, and must be collected at the appropriate time of maturity.

The “pineapples” or “maracas” are oval or spherical and have a length of about 20 cm. At their point of maturity they have a golden or red color with longitudinal stripes and emit a characteristic sound when hit. This sound is produced by the seeds contained inside the fruits, sometimes called cacao beans. These cocoa seeds, of bitter taste, are purple or white and look like almonds. The fat (cocoa butter), which seeds contain in large quantities, is used in the manufacture of medications, cosmetics and soaps. The pulverized residue, which is also called cocoa, is the raw material from which chocolate is manufactured.

Cocoa tree

Cocoa is obtained from the seeds of the fruit of this tree. After harvesting, the seeds are fermented to obtain their distinctive aroma. Cocoa contains almost 20% proteins, 40% carbohydrates and 40% fat and is very nutritive. Ivory Coast, Ghana, Nigeria and Brazil are the first producers.

Leaves, flowers and fruits of cocoa tree

Cocoa tree, originating from the tropical zones of the center and south of the American continent, has large leaves of bright green. The flowers, pink and white, appear inserted directly into the trunk or in the old branches. The fruits, like a capsule, contain many seeds that are allowed to ferment and then they are toasted and milled in order to prepare the chocolate.

Cocoa and chocolate manufacturing process

Once the fruits of the cocoa are collected, a long preparation process is started, known as the beneficiary of cocoa, which results in the raw material from which the chocolate industry will develop the derivatives of cocoa.

First the pulp and the seed are separated. This is done by fermentation, which develops the compounds responsible of the flavour. In the smallest plantations it is done by wrapping the pulp and the grains with largest leafs of banana tree or large wicker baskets, while in larger plantations it is developed in large wooden or concrete tanks.

Once clean, the grains are dried under the sun for about a week to remove humidity and improve his conservation. Sometimes the heat of the fire and drying chambers are used. When the cocoa sounds like crumpled paper, the drying is finished. Then the impurities, the broken or deficient seeds are removed and the cocoa beans are classified according to their size. Next, it is toasted, which is decisive in the development of the flavour and the color of the final product. Cocoa toasting is carried out with the purpose of decreasing the humidity content of the grains, developing the aroma and flavour of cocoa with the loss of volatiles and facilitating the elimination of the husk. There are two alternatives in the production process: the conventional toasting of the whole beans (at a temperature between 100 and 140 ºC for a time of 45 to 90 minutes) or subduing the beans to a previous heat treatment. The final product is known as cocoa beans.

The last phase consists in packaging, in paper or jute bags. Now the cocoa seeds are ready to be sent to the chocolate industry.

Toasted seeds are roughly milled and separated from the husk. In this way toasted cocoa is obtained, without the husk. The next phase involves a fine milling to obtain the paste or cocoa liquor. In this phase lies the secret of chocolate makers: the final product will depend on the selection and combination of the seeds.

The cocoa paste can be pressed to extract part of the fat and like this obtain the cocoa cake. If the residual fat of the cocoa cake is extracted with solvents, the disintegrated or defatted cocoa is obtained. The extracted fat is what is known as cocoa butter.

The butter, the paste and the cocoa cake and the cocoa without butter are the main ingredients in the chocolate elaboration.

Chocolate means the product obtained by a suitable process of elaboration from one or more of the following ingredients: cocoa beans without husk, cocoa paste, cocoa pressing cake, cocoa powder, partially defatted cocoa, cocoa butter, with sweeteners (white sugar, glucose, invert sugar or their mixtures).

According to its content of sweeteners, chocolate can be divided into sweet, semi-bitter or bitter. Chocolate may be added to milk, cream, whole or fractionaed seeds of almonds, hazelnuts, nuts, toasted and peeled peanuts, cereals, candied fruit or honey.

The chocolate texture is obtained with the kneading process (conching) that requires more than 72 hours and specialized machinery. The unctuousness and the texture depend on the conching. That, together with the flavour, determines its quality.

White chocolate is defined as the product obtained by a suitable process of elaboration from cocoa butter, milk powder, sugars (white sugar, glucose, invert sugar or their mixtures).

Characteristics of the gases emitted in the process

The gases emitted in the cocoa manufacturing process have the following characteristics:

  • Typical flow: between 6,000 and 40,000 Nm³ / h

  • Temperature: 60 ºC

  • Humidity: between 5.1 and 6.3% v / v

  • Concentration of VOC's: 250 mg/Nm³ of T.O.C. with peaks of 800 mg/Nm³

The emitted gases smell of chocolate.

Adequate tecnology to clean the emitted gases

Among the different technologies available for the elimination of odors, the most suitable for this application is a thermoreactor due to the following reasons:

  • It is a very proven and highly reliable technology.

  • Its maintenance is very low.

  • It does not need personnel in charge of the installation, due to the fact that operation is totally automatic.

  • It does not generate secondary waste as a consequence of the purification (as in gas scrubbers).

  • It is not affected by the presence of moisture (which don’t recommend the use of activated carbon) or lipid compounds (which don’t recommend the use of catalysts).

  • The operating cost is low: for every 1,000 Nm³/h of gases, 10 kW (8,700 kcal/h) in the burners and 2,8 kW in the fan.

These advantages compensate the somewhat higher cost compared to technologies such as gas scrubbing or biological beds.

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