Module 12. Cocoa and chocolate products

Lesson 44

 CHOCOLATE PRODUCTS – II

44.1 Production of Chocolate

The major ingredient of chocolate is cocoa mass, which is mixed with sugar, and in case of ‘milk chocolate’, also with milk powder. The conching process then follows, which is important for the development of full chocolate flavour. Melted cocoa butter is added, the chocolate mass becomes liquid and is cooled, tempered and poured into moulds to form chocolate products. The flow chart for production of Chocolate is given in Figure 44.1.

44.2 Mixing of ingredients

Sugar, cocoa mass and milk powder are intensively mixed forming a dry powder. This powder is pre-ground in various types of mills and then finely ground in a 5-roll refiner. The size of particles in chocolate is between 15-70 mm (average 25 mm). Small operators use vertical ball mills.

Optimum flow properties are required for further processing. The yield value required differs according to the potential use (e.g. hollow moulding or enrobing). The particle size affects both the yield value and the plastic viscosity.

In order to reduce recipe costs, the most expensive major constituent (i.e. fat) should be used in the smallest possible proportion which will give correct flow characteristics.

44.3 Refining

Refining is essentially a grinding process during which the broken cocoa bean cotyledons (i.e. nibs) are further reduced in particle size. The process is high temperature (250°C) for a short time because of the high pressure rollers used. The refining of sugar, cocoa butter and nibs promotes the formation of amorphous sugar which absorbs aromatic components and in turn masks burnt flavours from the sugar due to the high heat of refining.

The roasting process reactions may continue during refining, but it does not affect the flavour to the same degree as roasting. Steel roll refiners are used for precision grinding. An internal water circulation system ensures that the heat generated by the grinding action of the rolls is dissipated evenly and a constant temperature is maintained throughout the length of the roll.

An average palate cannot detect differences in fineness < 35 mm. The finer the chocolate, the better the gloss – as a smoother surface gives greater reflection of light. Finer particles provide greater adhesion and retention of fat, when chocolates are exposed to higher temperatures.

Fig. 44.1 Production of ‘Milk chocolate’ from cocoa mass

44.4 Cinching

It is the working of chocolate flake and crumb into a fluid paste. It produces the finest eating chocolate. It uses a machine ‘conche’, so named because of its resemblance to the conche shell.

44.4.1 Objectives

The objective of conching are as follows:

(a) Conversion of powdery, crumbly refined product into a flowable suspension of sugar, cocoa and milk powder particles in a liquid phase of cocoa butter.

(b) Allows the chocolate mass to be further mixed.

(c) Removes the undesirable flavour while developing the pleasant ones; bitterness is reduced, perhaps allowing other flavour notes to be more pronounced.

(d) Develops a mellow chocolate with a smooth mouthfeel.

(e) Develops the flow properties as well as flavour by coating the new surface with fat.

It is a mechanical treatment of chocolate mass in large containers fitted with rollers, paddles or a variety of other devices. The refined chocolate mass is placed in longitudinal/circular conche with other ingredients (i.e. cocoa butter, lecithin and flavouring). The outer casting containing granite beds and rollers are designed to hold single or twin pots. The pots are steam-jacketed and the temperature of the mass is thermo statistically controlled. Chemical and physical changes take place under the influence of air, which is brought into the mass, at a temperature of about 60°C and of rubbing and shearing process. The time taken for ‘circular Conche’ is about 7-9 hours.

Some manufacturers prefer to limit the conching time by restricting the conching process to primarily one of liquefying the chocolate. This is made possible by treating the cocoa mass at an earlier stage in order to remove some of the less desirable volatile chemicals.

44.5 Type of Conches

Batch Conches – (i) Longitudinal conches, (ii) Rotary (round) conches.

Continuous Conches.

44.5.1 Phases in conching process

44.5.1.1 Dry phase

Shearing, moisture evaporation, removal of other volatiles.

44.5.1.2 Pasty phase

Flavour development by means of shearing and heating, moisture removal, homogenizing.

44.5.1.3 Liquid phase

Homogenizing by means of intense stirring, shearing.

Cocoa butter is added during this phase of conching; chocolate mass becomes liquid.

A 0.15% reduction of moisture content obtained by intense dry conching is equivalent to a 1.5% saving of fat. The final reduction of viscosity is usually made at or near the end of conching by the addition of emulsifying agent lecithin @ 0.3%. One part of commercial lecithin can substitute for 9-10 parts of cocoa butter. Conching is carried out at 82°C for 0 to 24 h or even 44 h.

44.5.2 Effect of conching

In the Conche, the water content of chocolate masse is lowered from ~ 1.6% to 0.6-0.8%. As the moisture is removed, it takes with it many unwanted flavour components. In this way approximately 30% of short chain volatile fatty acids (viz., acetic acid) and up to 50% of low-boiling aldehydes are volatilized. Such removal of volatilized acid component is necessary to give the finished chocolate a full ‘rounded’ flavour.

The Strecker degradation, which starts during roasting is continued during conching leading to significant formation of free amino acids, contributing to flavour development.

There is rapid loss of phenols. There is loss of polyphenols through oxidation and enzymatic mechanisms (in tanning process) forming complexes with amino acids, peptides and proteins. The decrease in phenols during conching may be due to irreversible protein-phenol interactions. This reduces the astringency character of phenols, providing a more mellow chocolate after conching. The bitterness of cocoa mass is muted by the coating of the particles with cocoa butter. The same happens with sugar particles also. Clean sweetness of sugar is not as obvious in conched chocolate.

The head space volatiles decreased by almost 80% during the first hours of conching before leveling off. Conching continues the process of changing the Phlobatanins contained in the raw beans into brown or red, insoluble amorphous Phlobaphenes (this determines the colour of chocolate), which has already been partially accomplished by the roasting process (i.e. colour is enriched).

The previous grinding process will have created many surfaces, particularly of sugar, which are not coated with fat. These prevent the chocolate flowing properly when the fat is in liquid state. Conching process coats these new surfaces with fat and develops the flow properties as well as the flavour. The solid particles on being coated with a film of fat give rise to increased palate solubility. There is wearing off of the jagged edges of sugar granules giving chocolate a smooth feeling in the mouth.

44.5.3 Variables affecting conching

44.5.3.1 Temperature

Plain chocolate is conched at 71.1-76.7°C for about 10 h. Milk chocolate is conched at very much lower temperature. It should be sufficient to eliminate the fatty aroma of the milk, but not destroy the characteristic flavour of milk chocolate.

44.5.3.2 Time of conching

Since the temperature of chocolate masse determines the degree of liquidity of the cocoa butter and thus the length of time needed to conche, there exists a relation between time and temperature.

44.5.3.3 Size of particles

Controlling the particle size might allow for maximum conching. Larger particles require less cocoa butter per unit volume of coverage; it is easier to conche. More liquid the cocoa butter, the faster the conching and coating can proceed. The final degree of viscosity is very important; the melted chocolate must be sufficiently thin to fill all the cavities of the moulds.

44.6 Cooling and Tempering

It is critical to the appearance, gloss, shelf life and mouthfeel of chocolate i.e. the way it is cooled before solidifying in moulds.

44.6.1 Objectives of cooling and tempering

To develop a sufficient number of seed crystals to encourage the total fat phase to crystallize in a more stable polymorphic form. This in turn, will produce a better overall contraction and a more stable product.

Temper is the induced partial pre-crystallizaiton of cocoa butter. Tempering, in general, involves reducing the temperature of the chocolate to induce crystallization of both stable and unstable polymorphs. The temperature is subsequently raised to a point where the unstable polymorphs melt, leaving only polymorphically stable crystals which can then ‘seed’ the crystallization of the bulk chocolate in a stable polymorphic form.

It is the technique of controlled crystallization, which is necessary to induce the most stable solid form of cocoa butter in the finished product.

44.6.2 Polymorphism of cocoa fat

It is the ability of a molecule to crystallize in a number of different crystal packing configurations.

Six forms: Form I to Form VI

Three forms:  a (Alpha),   b (Beta prime) and b (Beta)

Form V is the state which is produced in a well-tempered chocolate. On lengthy storage, this can very slowly transform into form VI, a change which would occur after some hours or days. This results in a loss of gloss and the formation of white fat crystals (> 5 μm) on the surface of chocolate, the so-called ‘fat-bloom’.

If tempering is omitted, it results in:

(a) Fat bloom and (b) Softening of product.

44.6.3 Tempering process

The tempering steps include the following:

1. Complete melting
2. Cooling to the point of crystallization
3. Crystallization
4. Melting out of unstable crystals.

Tempering for ‘Dark chocolate’ would be 2-3°C higher than those indicated.

The liquid chocolate at a temperature of 45-50°C is cooled to 32°C, then to 27-27.5°C; stable and unstable crystals are formed during this cooling. The temperature is now raised to 30-32^oC, causing the crystals of unstable forms to melt.

 The actual temperatures for tempering chocolate vary depending on:

(a) the equipment used

(b) the fat composition of chocolate i.e. type of chocolate.

For instance, ‘Milk chocolate’ needs lower tempering temperatures than ‘Dark’ ones.

During tempering, the amount of solid particles is slightly increased and so too is viscosity.

After the tempering, the chocolate is still liquid, ready to be poured into the moulds i.e. pumped into enrobers or into the depositor of the moulding machine.

44.7 Moulding and Enrobing

Chocolate articles are made in two distinct ways (a) Moulding and (b) Enrobing.

44.7.1 Moulding

The chocolate is poured into the mould at 32°C; the filled moulds pass over a tapping section to remove the air bubbles. The moulds then moves on a belt through a cooling tunnel (7.7-8.3°C). After setting, the mould is turned upside down and as a result of volume contraction of cocoa butter, the article will easily fall out of the mould. Solid bars are then ready for packaging.

To make ‘Easter eggs’ and other ‘hollow products’, a small quantity of chocolate is poured into a split mould. The mould is then closed and put in a shaking machine to cool. The chocolate sets against the inner wall.

44.7.2 Enrobing

In enrobing, the liquid chocolate is poured over a solid centre. Many different products are made in this manner such as candy bars, biscuits, cakes and ice cream. In the well of the enrobing machine, the chocolate is again agitated gently and maintained at a temperature of 31-32°C. All the centers to be coated should themselves be a 26.1°C, as they enter the coating chamber of the machine.

This prevents undue expansion taking place in the cold centre, which otherwise causes:

(a) burst coatings, or

(b) retard cooling.

 The viscosity of the chocolate determines the thickness of the layer. This can be controlled with the fat content of the chocolate, which is usually a bit higher than that of moulding chocolate.

44.8 Cooling

The coated centres pass from the enrober to a cooling tunnel, controlled at a temperature of 7.7-8.3°C. The room should be air-conditioned. The room temperature should not exceed 22.2°C.

To cool and solidify chocolate properly, it must first be allowed to cool gently, in either radiant or gently moving air conditions. If the chocolate leaving the enrober is subjected to fierce cooling, it has effect of drawing the cocoa butter up to the surface of the product, quickly resulting in ‘fat bloom’.

The second stage of cooling may be by forced cooling at mild temperature (13°C) or by convection/radiation.

44.9 Packaging

The Packing room conditions should favourably be at 16°C, 55% RH.

The packaging materials should be able to protect product against moisture and against odours, which can easily be picked up by the chocolate fat. The outside of packaging must radiate the delicacy and luxury, which is the image of chocolate.

The packaging materials include decorative foils and papers. Polyethylene films of at least 100 m are used to provide protection against attack by insects. ‘Saran’ based on polyvinylidene is a vermin resistant package. Multi layered package can include Aluminium foil – Paper or heat-sealed foil – Cardboard box. Amongst the three layers, the centre one is impregnate with insecticide.

44.10 Storage and shelf life

Chocolate with its very low moisture content (< 1.0%) and natural antioxidants has a very good shelf life. The desired storage temperature is between 14.5 to 20°C. However, for ‘Dark covered chocolates’ and ‘Chocolates containing milk fat’ storage temperatures of 26.7-29.4°C and 22.8 -25.0°C is recommended respectively.

Irregular storage temperature may cause formation of ‘fat bloom’.

Other defects can be:

(i)  Sugar bloom

(ii) Production of off flavour upon prolonged storage due to production of delta-lactones (3,5-octadiene-2-one) from lipids.

44.11 Sugar and Fat Bloom in chocolates

Chocolate bloom is a moldy-looking white coating that can appear on the surface of chocolate. There are two types of bloom: Fat bloom, arising from changes in the fat in the chocolate; and Sugar bloom, formed by the action of moisture on the sugar ingredients. The unsightly crystals of fat and sugar bloom limit the shelf life of many chocolates. Chocolate that has ‘bloomed’ is still safe to eat, but may have an unappetizing appearance and surface texture.

44.11.1 Sugar bloom

While the most common is fat bloom, sugar bloom also occurs and is not necessarily distinguishable from the fat bloom by appearance. In freshly sugar bloomed samples, sugar bloom feels dry and does not melt to the touch, while fat bloom feels slick and melts. With fat bloom, the droplet simply beads up. With sugar bloom, the droplet quickly flattens and spreads, as the water dissolves the microscopic sugar particles on the surface. Alternatively, gentle warming of the surface will cause the crystals of fat bloom to melt, removing the appearance of bloom, while leaving sugar bloom unchanged.

Sugar bloom is caused by moisture. Condensation on to the surface of the chocolate or moisture in the chocolate coating causes the sugar to absorb the moisture and dissolve. When the moisture evaporates, the sugar forms larger crystals, leaving a dusty layer. It is caused by:

· Storage of chocolates in damp conditions

· Deposit of ‘dew’ during manufacture from damp cooler air or allowing chocolates to enter a packing room at a temperature below the dew point of that room

· Use of hygroscopic ingredients (low grade or brown sugars)

· High-temperature storage conditions of chocolate-covered confectionary, where the centers have a high relative humidity and the water vapor given off is trapped in the wrappings

44.11.1.1 Method to minimize sugar bloom

· Maintain an appropriate storage temperature (< 20°C) for chocolate products. A psychrometric chart is a valuable tool in determining the temperature above which food must be maintained in order to avoid condensation.

44.11.2 Fat bloom

It is generally accepted that visual fat bloom in chocolate is the cocoa butter that has separated toward the surface. It is caused by:

· Poor (incorrect/incomplete) tempering of the chocolate

· Incorrect cooling methods, including covering cold centers

· The presence of soft fats in the centers of chocolate-covered units

· Warm storage conditions

· The addition to chocolate of fats incompatible with cocoa butter

44.11.2.1 Methods to minimize fat bloom

· Maintain an appropriate storage temperature (< 20°C) for chocolate products

· Use an appropriate recipe for the fat (use compatible fat extenders)

· Add a bloom inhibitor such as surfactants like lecithin

Add seeding crystals

44.12 Uses of Chocolate

Chocolate can be consumed as such.

Much used as an ingredient on or in other foodstuffs e.g. enrobing of biscuits. Chocolate drops go into biscuits. Chocolate used in between wafers.

Chocolate is a popular flavour for desserts, ice cream, cakes, etc.

In UK, milk chocolate with typical crumb caramel note is predominant.

Cocoa flavour combines very well with many others; the popular combinations are Vanilla, peppermint, coffee and orange. Fruit flavours include nuts, cardamom, etc.