The Manufacturing Process of Chocolate and Final Product Analysis.

As the focus of this report is on the mixing and shaping of chocolate, only the conching and moulding/cooling processes will be looked at in detail.

Bulk Ingredient Mixing

Before the milling (process to reduce the particles sizes of ingredients) of the ingredients, they will need to be mixed together. Cocoa liquor, granulated sugar, milk components and some cocoa butter are mixed together in a heavy duty mixture to create a uniform paste with the appropriate consistency for it to go through the milling process.

Conching

The main mixing process used in the production of chocolate is conching. There are two different aims of conching. The first is for flavour development, the flavour components of the chocolate are produced earlier in the process when the cocoa beans go through fermentation and roasting, as well as the pleasant taste of chocolate these processes also produces astringent/acidic ones which are removed in the conching process. The second aim of this process is to turn the chocolate from its powder, flaky or thick dry paste form into a free flowing liquid that can be used to make the chocolate in further stages. 

Conching can be split into three phases called dry conching, the pasty phase and liquid conching. When the chocolate first enters the conching machine it is a powder containing excess moisture which is detrimental to the flow properties of the chocolate. The powder is mixed at an elevated temperature to remove some of this excess moisture which also allows for the removal of some of the acidic content improving the flavour of the chocolate, the escape of the moisture is made easier because a lot of the surfaces are not coated in fat.

As the temperature in the conche rises cocoa butter melts which causes the particles to stick together producing a paste. This paste contains many particles which are not coated in fat and need to be coated because the proper coating of these particles will mean that the chocolate will melt at body temperature. The thickness of the paste has a big effect on this process; a thick paste will give a higher chance of particles being coated by the shear/ smearing action of the conche while in a thin paste particles will just be moved around and not coated in fat. It is therefore important that the paste is kept as thick as possible for as long as possible.

The final function of conching is to give the chocolate the correct flow properties so that it can be used in the next processing steps. This stage can also include the addition of fats and emulsifiers which thins the liquid chocolate and reduces the amount of mixing which can take place.

Conching machines have rollers or paddles which continuously knead/ mix its contents over a period of hours or days depending on the quality of chocolate. There are number of different conching machines available these include the long conche, the rotary conche and continuous low volume machines.

The main process that takes place during conching is the movement of flavour molecules between the components of chocolate. At the beginning of the process the flavour is concentrated on the surface of the cocoa particles and in the fat while the sugar has none of the flavour. By the end of the process the flavour is transferred to the sugar giving a near uniform distribution of flavour of these components as can be seen in diagram. 

Other changes seen in the conching machines are the removal of acid which is reduced when excess moisture is removed. This change is at its biggest near the beginning of the process and decreases over time as can be seen in diagram.

Moulding

The shaping of chocolate is done using moulds. This can include solid bars, hollow chocolates (like easter eggs) and chocolates filled with other ingredients. The moulding process starts with the tempered chocolate being deposited into a mould with a mirror image of the desired design. The moulds are shaken to evenly distribute the chocolate and to remove air pockets which would cause the chocolate to have holes. The mould can also be scraped to remove any excess chocolate before it enters the cooling area. Once the chocolate is sufficiently cooled it can be removed from the mould by inverting it and either tapping or twisting the moulding depending on the material that the mould is made from.

The main types of moulds include solid, shell and hollow moulds. Moulds can be made up of either metals or plastics and the plastics are the more common type. The distribution of chocolate is done through a depositing head which contains nozzles. The amount of nozzles in the depositing head is equal to the amount of indents in the mould below it. The nozzles are designed so that they can deposit an exact weight of chocolate into the mould. The transporting mechanism sometimes lifts the moulds until they are very close to the nozzles. When the right amount of chocolate is in the mould they are then lowered very quickly which will break any strands of chocolate between the mould and nozzles a standard nozzle can be seen in the diagram.

Technical challenges that must be overcome

The properties of chocolate such as its glossiness and the way it snaps are dependent on the structure of the cocoa butter. Chocolate contains a continuous phase of cocoa butter which is substantially crystalline at room temperature and makes up between 30 and 35% of the total chocolate, in which sugar and cocoa solids are suspended.

Cocoa butter is polymorphic and can exist as one of six different structures, these are numbered I to VI. The following tables show some of the properties of these structures and the properties that they give to the chocolate.

        Table: Cocoa Butter Polymorphs,

As can be seen in the above table the preferred form of cocoa butter crystals is form V. This crystal form is made in the tempering process. The tempering process is the controlled cooling of liquid chocolate with agitation to form the right forms of fat crystals within the chocolate. Agitation, temperature and time are all important factors in the tempering process and the right conditions will give chocolate most of its important properties such as a good snap and gloss, proper texture, bloom resistance, contraction for easier demoulding and an increased shelf life. 

As stated previously the moulding process will include a section where the vibration of the mould is needed to remove air bubbles from the liquid chocolate before it is solidified. Liquid chocolate is a Non-Newtonian fluid and has a yield value which stops air bubbles within it rising through the fluid. A shaking system operating at the correct amplitude and frequency causes the chocolate to act as a Newtonian fluid reducing the viscosity of the liquid chocolate making it easier for the bubbles to be removed. An example of the reduction of the viscosity of an example milk chocolate with increasing frequency at three set amplitudes can be seen in diagram . This graph shows that it is important to select the correct value for frequency and amplitude as  low values will only mean that energy is being wasted and only very minor changes in viscosity are made and very high values will also be a waste in energy as the viscosity can only decrease to a point and any further energy input will not show positive changes in the viscosity and can even increase its viscosity from it minimum value. 

Product evaluation

Flavour

The testing of chocolate flavour is done by sensory panels. The reason for this is because there are no correct flavours and in different countries there are different favourites. There are instrumental methods in the testing of chocolate flavour but these are more to do with determining off flavours and odours rather than the actual chocolate flavour. These instruments include artificial noses and liquid chromatography.

Texture

The testing of texture is also done by sensory panels but as they are expensive, the testers can only evaluate a few samples per day and it is hard for small changes in texture to be detected because of this it is important to have some instrumental methods. The snap and hardness are important properties for chocolate bars. Snap can be tested by a three point bend test, where chocolate is made into a uniform bar and kept at a constant temperature for an extended time to make sure the test is accurate. The hardness can be tested by texture measuring instruments which drive blades or probes into a sample measuring the resistive forces.

Conclusion

Stability and Shelf-Life of Food

http://www.rsc.org/education/teachers/learnnet/inspirational/resources/4.1.4.pdf

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