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Chocolate are semi solid suspensions of fine solid particles from sugar and cocoa. In another words we can say chocolate is a complex emulsion made by mixing cocoa mass, cocoa butter and sugar (sucrose). Chocolate is luxury food that during consumption and provide pleasant sensation. (1,2,3)
Primary chocolate categories are dark, milk, white that differ in the cocoa solid, milk fat and butter content. Some times the classifications based on the cocoa content like sweet chocolate and bitter chocolate because the sweet chocolate contains 25% of cocoa or less than that and 60% and above for the bitter chocolate. The main source of this cocoa is fruit of Theobroma cocoa. The chocolates are in continuous phase lipid composition, which influences mouth feel and melting properties. Chocolates are generally solid at ambient (20-25ÂÂÂÂ°C) and melt at oral temperature (37ÂÂÂÂ°C)(2). Report published by IBIS World states that the chocolate and confectionery manufacturing industry will grow by 1.1% in the last five years to 2009-10(4). While following chart shows the percentage share contribution of chocolate in sweet confectionary.
Fig.1. Pie chart shows % share contribution of chocolate
Chocolate has major share in sweet and chocolate confectionery; hence it is necessary to understanding the factors influencing chocolate microstructure, texture, rheology and appearance. Rheological properties of chocolates plays important role in
Manufacturing process of chocolate to get high-quality products as well as well-defined texture(5). This will help to improve quality of chocolate. Appearances, texture of chocolate are key parameters in consumer choice and acceptability. In this study our aim to reduce the problems with chocolates like its inconsistency in melting and coarse texture. These problems are all related to the chocolates rheological behaviour. So the problems mainly arise due to the particle size, particle size distribution and ingredient composition within a particular chocolate type. Following table 1 shows types of chocolate and major constitution.
Table 1. Types of chocolate and major constitution (1,6)
fat content %
So as shown in above table, any changes in content of constituent may affect the final product of chocolate. Fat content exerted greatest effect on texture and appearance. On the other hand the other factors like the processing and storage conditions affect the chocolate performance change its texture and its melting behaviour. During processing moisture and water content is an enemy of chocolate and show seizing of chocolate. It necessary to avoid water in the production of chocolate. The polymorphic forms of the chocolate has directly influenced on problem associated with chocolate melting inconsistence and coarse texture.
Problem in chocolate
Some of the important problems associated with problem manufacturing are summarized in following table 2
Table 2. Important problems associated with chocolates
Particle size and particle size distribution
Surface roughness, coarse structure
Improper conching and tempering
Inconsistent melting behaviour
Selection of wrong polymorphic form or lack of tempering process
Unpleasant mouth felling
Particle size and particle size distribution
We have already mentioned some problems related with the chocolate due to the manufacturing or constituent problem but we have some other problems related to the textural behaviour or its textural problems like poor caramel texture or gritty or grainy texture. This is briefly explained in following table. 2
Table 3. Textural problem, cause, solution(7)
Poor caramel texture
Too thick or poor elasticity
Decrease milk protein level
Increase milk protein level to increase viscosity
Gritty or grainy texture
Change in sugar crystal type
Large sugar crystal formed
Sugar crysatal formed on product surface
adjust balance or levels of sugar type for proper crystallisation
reduce lactose content. Check seeding and agitation during heating and cooling
optimise storage condition
The problems for chocolate are mentioned earlier that is the coarse structure and inconsistent melting. Rheologically, molten chocolates behave as non- Newtonian liquids with yield stress (minimum amount of energy to initiate fluid flow) and plastic viscosity (energy to keep fluid in motion) dependant on processing quality in finished chocolates is highly depending upon inherent particle size distribution(8). And rheological properties determine efficacy of mixing, conching, tempering. To solve these problems it is necessary to think on production, packaging and storage issue. But production sector is only where quality of chocolate largely depends. Hence we mainly focus on production criteria.
Manufacturing out line for chocolate
General outline for manufacturing of chocolate is basically divide into four steps,
4) Tempering (most important)
Schematic representation for chocolate production is as follows.(9)
Fig. 2 schematic flow chart of chocolate preparation
As name suggest in this step mixing of ingredients such as cocoa power, cocoa butter/liquor, sugar and milk power to form a pasty mass by using suitable mixing instrument. Various quantities are use depending upon nature of final product required(1).
The pasty mass is passing through roller to achieve desire particle size mainly less than 35 micrometer in case of dark chocolate. But particle size is affected by nature and quantity of ingredients used. Objectives of this step are (2,3)
-Particle size reduction
-breakdown of agglomers
-uniform particle distribution
The refined product is then entre in to stage 3.where final viscosity of the product is created. Also texture is maintained. Agitation is required at temperature greater than 500 C for several hours.(2) The length of conching process helps in determining final smoothness and quality of chocolate. For good quality of chocolate it is required to at least for 72 hours. Addition of remaining ingredients takes place to achieve final desire viscosity of the product.(1) Conching temperature and time varies and depending on type of chocolate and quality of chocolate.
The final process is tempering. A very precise cycle of heating and cooling takes place to get the stable crystals. Here controlled precrystallisation is carried out to achieve most suitable polymorphic form of cocoa. If cocoa butter undergoes uncontrolled crystallization, results in crystals of varying size. Varies to various size and even large enough to be clearly seen with the naked eye. This will result into mottled and matte surface of the chocolate. Some time even it breaks(1). When we melt the chocolate and let it cool it will set as unattractive, dull brown mass streaked with grey its texture when eaten will be chalky and grainy. Tempered chocolate, on the other hand, is shiny, even coloured, crisp, smoothing tasting and give pleasant mouth fell. So chocolate tempering is also the problem for inconsistent melting of the chocolate. The trick to tempering is to control the temperature of the melted chocolate very precisely first cooling it and then reheating slightly. Tempering is the process which controls the all the polymorphs of cocoa butter. Nowadays this tempering is done with computer controls. And it needs controlled and skilled stirring of the chocolate. An appropriate polymorphic form is crucial to achieve final product quality including surface, hardness and colour. Tempering process is mainly divided in to 4 steps.(10,11)
1) Melting to complex at 500C
2) Cooling to point of crystallization at 320C
3) Crystallization at 270C
4) Conversion of any unstable crystals 29-310C
Fig.3. Tempering sequence during lipid crystallization in chocolate(1)
Tempering involves slowly raising and lowering the temperature of melted chocolate while constantly stirring. This process causes the structure of the large cocoa-butter crystals in the chocolate to repeatedly break and then reform. When the chocolate is finally allowed to set again, the crystals of cocoa butter join in perfect chains, creating an extremely smooth, shiny chocolate that has a clean snap when broken. Following table 4 shows tempering temperature for different types of chocolate.
Table.4. Tempering temperatures (2,3)
then cool to
bring the temperature back
up to 32.32Â° C
then cool to
bring the temperature back
up to 30Â° C
then cool to
bring the temperature back
up to 27.77Â° C
Several steps are involved in production of quality chocolate. It will start from selection of raw materials, production line and last but not least storage of chocolate.
Here we majorly concentrate on problem related production steps to solve this problem.
Particle size distribution is a key determinant of the flow (rheological) properties in chocolates with a direct influence on sensory perception.(12)Beckett and et.al concluded that the largest particles are gives pleasant mouth feel sensation with respect to grittiness, but the smaller ones are more important with respect to chocolate flow properties. Bimodal particle size distribution Promoted viscosity reduction and better mixing Yielding improvements in final product shear, time and temperature Stability.(13) General particles diameter ranges from 20-30 micrometer and a ratio of 60% coarse particles to 40% fine particles can be used to get both properties.
Texture change in chocolate is usually due to uneven temperatures or stirring.
Agitation is required at temperature greater than 500 C for several hours. Generally it will take 60-72 hours depending on quality of chocolate you want. The undesirable crystal form occurs only when the mix was processed within a very narrow regime of temperature and stirring. If conching time increases it will give good quality of chocolate but due to increase in production time line, cost of chocolate also increases.
Tempering of chocolate is heart process for manufacturing in chocolate. Final quality of chocolate is largely depending on success of this process. Objective of this process is converting of fatty material into suitable stable form. Cocoa has properties of showing polymorphic form. Most suitable polymorphic form for production of quality chocolate is firm v.
5.3.1 Polymorphism/ lipid crystallisation
Cocoa butter can crystallise in a number of polymorphic form as a function of triglyceride composition. Cocoa butter has six polymorphic forms (I-VI). Form V Î² is the most desirable form in well tempered chocolate, giving a glossy appearance, good snap, contraction and resistant to bloom.(fig.4) This form has optimal density, melting behaviour, and surface appearance. This form is the second most stable form. Form VI is the most stable but has main cause of fat blooming and gives hard chocolate and takes weeks to form. Table 6 shows Melting point of the polymorphic forms of cocoa butter with properties.(1)
Fig.4. Polymorphic form structure (14)
Table 5. Melting point of the polymorphic forms of cocoa butter(1,10,14)
17Â Â°C (63Â Â°F)
Soft, crumbly, melts too easily.
21Â Â°C (70Â Â°F)
Soft, crumbly, melts too easily.
26Â Â°C (79Â Â°F)
Firm, poor snap, melts too easily.
28Â Â°C (82Â Â°F)
Firm, good snap, melts too easily.
34Â Â°C (93Â Â°F)
Glossy, firm, best snap, melts near body temperature (37Â Â°C).
36Â Â°C (97Â Â°F)
Hard, takes weeks to form.
If chocolate is poorly tempered the outcome is the Î² form IV which rapidly transforms into form V. In cocoa butter forms V and VI are the most stable forms. Form VI is difficult to generate although formed lengthy storage of tempered chocolate accompanied by fat bloom. And other point it has 36Â°C and crystals that are large gritty on the tongue(1). And other forms has different melting point and has different textures. Surface roughness, coarse structure and inconsistent melting behaviour of chocolate can be avoided by selecting proper polymorphic form. Selection of form v is very essential.(10,14) Maintaining temperature is also important factor to get form v. But it is difficult to maintain temperature of bath in large scale production. Distribution of even temperature throughout the bath is quite difficult. This problem can be solved by using heating coil at different corner of the bath. High degree Temperature sensors must use at different corner which is controlled by computerised program. Also in process analysis of chocolate mass is essential to understand and identification of a particular crystalline form converted during process. It will help to avoid under tempered or over tempered chocolate. Following figures 5 shows difference between under tempered chocolate, optimum tempered and over tempered chocolates at two different time period. (1,10,11,14)
Fig 5. (a) Fresh and (b) matured (conditioned) optimally-tempered, under-tempered and over-tempered dark chocolates,(15)
Overheated chocolate will lose the silky shine of melted chocolate and become thick and muddy. The best way to melt chocolate is to keep the water in a double boiler hot (but not boiling), and to employ a chocolate or instant-read thermometer while melting the chocolate. IfÂ the process isÂ upset atÂ any one ofÂ the tempering stages, this will beÂ reflected inÂ the appearance and consistency ofÂ the chocolate. For example, aÂ characteristic white bloom can appear onÂ its surface. Such aÂ "bloom" isÂ the result ofÂ incorrect tempering. Moreover, the "bloom" does not appear atÂ once, but some time later. Also, the chocolate can become hard-grained and crumbly due toÂ incorrect cooling. InÂ this case, its taste properties will beÂ retained, but its appearance for marketing purposes will beÂ hopelessly damaged. Hence it is very important to understand tempering process and find out optimum tempered range.
The temperature and mixing control by using temperature sensor eliminate inconsistent melting and coarse texture problem and it will help in savings in production time and reduce cost of the final product.
The packaging material used in chocolates play an essential role in preserving the quality of the product. Chocolate packaging materials consists of numerous types: -Oriented Polypropylene film- a transparent film with moisture and fat barrier. -Pearly-zed Oriented Polypropylene film or cogitated core - an opaque material which is mainly used for bar wraps as it possesses the stiffness of glassine. -Vacuum Metalized Polypropylene film which has increased moisture barrier and a metallic-like appearance primarily used in pouches. -Thin aluminium foil used for packing chocolate -Engraved and embellished metal containers for holding larger quantities of chocolate. -Moralized paper and cardboard cartons used for merchandising chocolate boxes.
These above said packaging materials are used in chocolate manufacturing to prevent the chocolate from the environmental conditions like moisture, temperature etc. which cause the chocolate melt and its bloom(16).
Chocolate should have a glossy surface, which must be free of fat and sugar bloom, and a compact, homogeneous texture. Well conched chocolate forms a homogeneous mass with a smooth mouth feel and without graininess on the tongue. It breaks cleanly and must not crumble. Storage conditions for chocolate related temperature and humidity are summarised in Table 7.
Table 6. Storage conditions for chocolate.(17)
Relative humidity in (%)
Storage room (ambient)
77.0 / 23.0
35.0 / 1.7
-17.0 / -22.2
The detrimental effects of moisture on chocolate viscosity and the ease of processing have been observed. When the melted chocolate comes into contact with water, the dry particles become moist and begin to stick together, quickly form a gritty, rough mass of chocolate.Â To prevent chocolate from seizing is to eliminate any chance of the chocolate coming into contact with water. Always make sure the bowls and utensils you are using are perfectly dry. Avoid using wooden spoons or boards, as they might retain moisture and impart this moisture to your chocolate.Â NeverÂ cover warm chocolate with a lid, as the heat of the chocolate might form condensation on the inside of the bowl, which will cause the chocolate to seize. In order to prevent the chocolate taking up moisture,(2) advised to keep the equilibrium relative humidity (ERH) at around 35-40% during manufacturing.
Analysis of chocolate
Chocolate texture can be evaluated by using instrumental measurements. But cheap and effective method is use of sensory evaluations and statistical evaluations can be performed(18) Sensory evaluations include visual inspection of gloss, colour, shape, roughness, and surface can be tested. Also taste evaluation can be perform. This will help in find out the quality of chocolate.
High degree Temperature sensors must use at different corner which is controlled by computerised program. Also in process analysis of chocolate mass is essential to understand and identification of a particular crystalline form converted during process. It will help to avoid under tempered or over tempered chocolate.
In process analysis of chocolate mass is essential to understand and identification of a particular crystalline form converted during process. It will help to avoid under tempered or over tempered chocolate
In case of Tropical regions
In case of tropical region where ambient temperature is more than 40 oC (Nigeria), consumption was less. Because chocolate imported into the tropical region melts at ambient temperature, resulting into formation of bloom on surface upon storage. This problem can be avoided by increasing melting temperature of the chocolate. So study focused on development of thermo resistant chocolate which will remain stable at ambient temperature in tropical region. But cocoa butter which is major constituent of chocolate melts sharp at 350C or softening around 30-320C. Addition of various quantities of cornstarch and gelatine significantly increases the melting point of chocolate. Use of cornstarch at a 10% and gelatine 10% in the standard chocolate recipe produced chocolate of elevated melting point (450C-500C). But excessive addition of both ingredients has a problem while mixing which become difficult. Sensory evaluation of the cornstarch chocolate shows no significant difference at 5 per cent probability level for colour, taste, smoothness and overall acceptability, but there was a significant difference in the sweetness of the chocolate product, when compared with the milk chocolate. Also, there was no significant difference at 5 per cent probability for colour. Sweetness and overall acceptability for chocolate made from gelatine.(19)