GB2151454A - Manufacture of roasted cocoa and a roaster therefor - Google Patents

Abstract

Roasted cocoa is produced by (a) crushing raw cocoa beans and partially removing the husks, (b) drying the beans to a moisture content of 3-4%, (c) separating the husks from the kernels, (d) comminuting and drying kernels to 2-3% moisture content under vacuum. (e) roasting the kernels in a thin moving layer and (f) cooling the roasted kernels. This produces an evenly roasted cocoa with good aroma. The roasting step may be performed in a cylinder (1) surrounded by a heating jacket (2) divided into three zones. Cocoa is supplied via aperture (6) and is picked up by wiper blades (12) rotating on shaft (11) and the cocoa is distributed as a thin layer on the wall and roasted. The temperature inside the cylinder is measured by sensors (13) and results transmitted to (14) and control (15) which can alter supply of heat to the three zones. The roasted cocoa is discharged at outlet (16) and hot and/or dry air may be supplied via aperture (7) and discharged via outlet (9) with any entrained cocoa being stopped by baffle (17). <IMAGE>

Description

SPECIFICATION A method of and an apparatus for the continuous manufacture of roasted cocoa mass The invention relates to a method of manufacturing roasted cocoa mass, in which the cocoa beans are processed by drying, husk-removal, crushing, comminution and roasting to produce a roasted cocoa mass, and also to a roasting apparatus.

In chocolate manufacture, roasting plays an essential part with regard to quality of the finished product, particularly with regard to aroma and flavour properties. To-date, the practice has been almost exclusively to roast, i.e. to heat for a certain time to temperatures of up to about 1 50 C, cocoa beans from which the husks have been removed and which are either whole or only coarsely crushed. With this practice, two basic problems arise. One resides in the relatively large dimensions of the particles of roasted material and their greatly differing size distribution, the great temperature gradient between the surface of the roasted particles and their centre, so that over-roasting and/or under-roasting must be inevitable. The other lies in the very high content which may persist in the raw cocoa beans.As fundamental investigations have shown, a high water content at the commencement of roasting hampers and in extreme cases may even prevent altogether the aroma reactions which take place during roasting.

In order to avoid these disadvantages, it has been proposed firstly to remove the husks from and then pre-crush the raw cocoa beans, possibly subjecting them to a preliminary drying process, followed by cleaning, grinding the crushed cocoa into a viscous composition which is then roasted in a thin layer, further procedural steps being interposed or subsequently applied (DOS 2 238 519).

With this procedure, raw whole cocoa beans are dried, crushed and cleaned. The disadvantage with this process resides in the low process speed due to the fact that whole beans are being dried. The reason for this is the relatively low rate of diffusion of water from the interior of a cocoa bean. Also, there is always a moisture gradient within the cocoa bean. A further disadvantage lies in the fact that when pre-drying whole beans, cocoa butter diffuses into the husk and is then lost when the husks are separated from the crushed kernels.

Preliminary drying preferably takes place at a negative pressure. This does however entail the disadvantage that the aroma precursor compounds which are not highly volatile at normal pressure are expelled to a greater degree.

Where the plant is concerned, most equipment will meet the technical requirments.

However, what is not satisfactory is the result obtained from thin-layer roasting. According to DOS 2 238 519, every attempt should be made as far as possible to maintain the optimum roasting temperature. Fluctuations of only i 1 .5,C are permitted. In addition, this optimum temperature must be maintained in the total length and depth of the thin layer.

To achieve these conditions, it was already proposed in German Patent No. 297 888 for the raw cocoa beans from which the husks had been removed to be comminuted and roasted on smooth moving heating surfaces in a still and thin layer. It is proposed in DOS 2 238 519 that the roasting process be carried out on a belt or roller apparatus but still in a stationary layer.

However, tests have shown that even in a stationary thin layer, noticeable temperature gradients occur and the elimination of moisture from and degassing of the stationary thin layer are incomplete. The gas and vapour bubbles enclosed cause foam formation.

According to DOS 1 919 870, roasting should be carried out with agitation and in an enclosed container. In comparison with roasting, degassing in thin still iayers is better but even greater temperature differences arise in the cocoa mass which is to be roasted. With all the known roasting apparatus, there is only inadequate opportunity for influencing the temperature profile while is to be adjusted.

Accurate observance of a predetermined temperature-time regime is however the most essential prerequisite for optimum roasting of the cocoa mass. Therefore, accurate process control has a decisive influence on the result of the process. The necessary detection of the distribution of temperature in the material over the length of the apparatus is at present carried out in very expensive constructions which have apertures passing through the walls of the stator, the number of points of measurement being generally limited while the susceptibility to interference is very high due to the holes in the stator walls and the fact that the temperature sensors are stationary. In many cases, detection of the temperature profile is dispensed with entirely and only the temperature of the material at emergence is recorded.In plant where co-rotating measuring probes are used, the signal obtained by measurement is usually transmitted through slip rings to the stationary parts of the plant.

These difficulties from the point of view of measurement technology do in the case of all methods and equipment mentioned for thinlayer roasting give rise to factors which are intolerable in principle in process control, factors which are unacceptable to the assurance of constant product quality.

The object of the invention is to obtain an evenly roasted cocoa mass with optimum yield of the aroma potention.

The problem is to indicate a method wherein, prior to the roasting process, the water content in the material to be processed is sufficiently low in comparison with the initial state for further processing and wherein the temperature profile during the roasting process is locally regular and optimum over the entire roasting time.

According to the invention, from the procedural point of view, the problem is resolved by the following sequence of stages: --crushing, preliminary husk removal and preliminary separation of raw cocoa beans, -preliminary drying of the crushed cocoa beans to a moisture content of 4% to 3% at a temperature of 40"C to 90"C, -separation of the crushed kernels from pieces of husk, -omminution of the crushed kernels and secondary drying to a moisture content of 3% down to 2%, utilising the heat energy released during comminution and at a negative pressure of up to 0.5 atm roasting of the cocoa mass in a thin moving layer and with a continuous passage through temperatures of 100"C to 140"C, -cooling of the fully-roasted cocoa mass.

Preferably, preliminary drying is carried out at a temperature of 60"C to 80"C while the secondary drying process takes place up to a moisture content of about 2.5%, the secondary drying temperature amounting to a maximum of 90or.

With this proposed method of proceeding, the process speed is increased which is founded in the faster drying of the already pre-crushed beans (smaller parts and larger surface area). Thus, too, less heat energy is required. Since even prior to drying a major part of the husk material is carried away, there is also less loss of cocoa butter.

From the point of view of the apparatus, for the thin-layer roasting in a moving thin layer, a roasting apparatus of the following description is suggested: -a cylindrical heatable basic body is inclined in a variable position and is rotatable, -a plurality of rotating wiper blades are radially adjustably located in known manner inside the basic body on a centraily located shaft, --on at least one wiper blade there are, at a selectable distance from one another, a plurality of temperature sensors connected by conductor elements to a measured value process ing and transmitting part located on the shaft end -upstream of the measured value processing and transmitting part but not connected thereto there is an evaluating and control part which is connected to a process computer and/or recording and indicating apparatus.

The heating means is sectionally regulable and is disposed on the periphery of the basic body. The temperature sensors can be spirally staggered on all wiper blades and are built up on a semi-conductor base. In the measured value processing and transmitting part and also in the evaluating and control part there are in each case a transmitter and a receiver for bi-directional signal transmission.

Signal transmission takes place on a basis of infra-red rays. In the case of this proposed roasting apparatus, the roasting process can be clearly controlled. In particular, the temperature profile and the roasting temperature can be exactly controlled at all points and so the entire aromatic substances can be fully exploited.

It is intended to explain the invention in greater detail hereinafter with reference to an embodiment. The method of procedure is shown as a flow diagram in Fig. 1. Where the process is concerned, following a preliminary cleaning, the raw cocoa beans are crushed to provide crushed kernels and the loosely clinging husks are separated therefrom. In order to avoid as far as possible any losses of material and aroma precursor substances, these crushed kernels are subjected to preliminary drying at temperatures of 60"C to 75"C in a fixed bed dryer operating on a continuous basis with drying media conveyed on a crossflow principle, the moisture content at emergence being necessarily 3.5% Ma to 4% Ma, which must be respected.The pre-dried crushed kernels obtained in this way are subjected to a cleaning process in which at least 99% of the husks are separated off, followed by comminution, regulation of the negative pressure in the grinding equipment to values of normal pressure at most and to a minimum pressure of 0.6 bars, it must be possible to achieve a final moisture content of at least 2.5% and at most 2%.

The cocoa mass which is pretreated in this way in the apparatus according to the invention is roasted, de-gassed and de-humidified under normal pressure with no additional in feed of hot and/or dry air, a temperature profile being maintained which is character ised in that in the first third of the length of the apparatus the cocoa mass is heated to 1 25 C and is kept at a constant 1 25 C over the remaining two-thirds. To achieve this, heating medium temperatures of about 1 40 C are required in the first third and of about 1 25 to 1 30 C in the remaining two-thirds.

The dwell time in the roasting zone amounts thereby to some 40 to 60 seconds. The roasting time can be controlled by the inclined position of the roasting apparatus according to the invention. After it leaves the apparatus, the roasted, de-humidified and de-gassed co coa paste is rapidly cooled to a temperature of less than 80 to 85"C. The cocoa paste which is thus manufactured has a water content of about 1% by weight and thus very good flow and processing properties. Ascertained by the senses, the aroma quality of the cocoa mass which is roasted and pretreated in this way is characterised by a strong balanced cocoa aroma, pleasant bitterness, little astringent and acid.

The process of roasting in a moving thin layer can be carried out according to the invention in an apparatus such as is shown diagrammatically in Fig. 2. Fig. 3 shows a cross-section taken on the line A-A in Fig. 2.

The roasting apparatus consists of a cylinder 1 with, sub-divided into heating zones 2, a double casing to accommodate a heating medium. The illustration is of an advantageous embodiment which has three heating zones.

The double casing is in each zone provided with pipe connectors 3 for the supply of heating medium and pipe connectors 4 for the discharge of heating medium. At the intake end 5 of the cylinder 1 there is an aperture 6 for the in-feed of unroasted cocoa mass and a connector 7 for the supply of hot and/or dry air. Provided at the other end of the cylinder 1 is a separator assembly 8 in which there is an orifice 9 for the discharge of roasting gas and of the hot and/or dry air which was introduced into the apparatus. The actual separating head 10 is disposed inside the separating assembly 8.In the interior of the cylinder 1 and of the separating assembly 8 there is a shaft 11 which is axially orientated in relation to the cylinder 1 and separating assembly 8 and which carries a plurality of wiper blades 1 2 which are orientated radially in respect of the cylinder 1. As Fig. 3 shows, an embodiment has been chosen which has four wiper blades. The outer edges of the wiper blades 1 2 are at a finite distance which is greater than 0 from the inside wall of the cylinder 1, which can if necessary be of variable design.The entire apparatus is normally disposed in a horizontal position but can, however, be moved into an inclined position so that the resultant gradient between the inlet end of the cylinder 1 and the separating assembly 8 can favourably influence the flow conditions and thus the dwell time in relation to the method according to the invention.

The temperature profile of the cocoa mass is measured along the double-cased cylinder 1 by temperature sensors 1 3 which are preferably constructed on a semi-conductor basis and disposed along the edges of the wiper blades 1 2. These measuring sensors 1 3 which can be mounted on either one or on a plurality of wiper blade edges are distributed over the total length of the wiper blades 12. A particularly favourable arrangement consists in a somewhat denser distribution in the vicinity of the entrance to the cylinder 1 and in a less dense distribution in the vicinity of the transition from the cylinder 1 to the separating assembly 8 since it is possible thus to detect close to the intake any particularly marked axial temperature gradients.The temperatureanalogous signals generated by the temperature sensors 1 3 are, according to the invention, transmitted per wire to a measured value processing and transmitting part 14 disposed at the separator end of the shaft 11, whence they are transmitted through a bi-directional, non-contacting and advantageously disturbance-free transmission path based on infrared radiation to a stationary evaluating and control part 1 5. Enquiry of the individual temperature sensors 1 3 and thus recording of the temperature profile can take place both automatically, by process computer control or also by hand. The measurement arrangement according to the invention, on the on-line principle, provides facility for possibly process computer-supported control of the temperature profile.

A particularly advantageous embodiment of measured value detection and measured value processing system 14, 15, including the relevant temperature sensors 13, will be described hereinafter. Used as measuring sensors are high frequency transistors, of which the temperature-dependent base-emitter voltage at constant current flow if utilised.

Switch-over between the individual points of measurement is effected via analogue measurement point selecting switches controlled by a sliding chain. The temperature-analogous signals present in the form of a voltage are converted in a voltage frequency converter into a sequence of pulses, whereupon they are transmitted by an infra-red ray unit without contact and in such a way as to be insusceptible to interference. These functional units are disposed on the measured value processing and transmitting part 1 4 which is located on the shaft 11. In the contactlessly precedent evaluating and control part 15, the sequence of pulses arriving with the infra-red rays are received, further processed in a counting mechanism, indicated digitally and, after digital-analogue conversion, recorded on an analogue recording and indicating apparatus.At the same time, the stationary part 1 5 ensures control of the part 14 through the bidirectional infra-red transmission path by which the commands for the sliding chain, synchronisation and the timing for the voltage frequency converter are transmitted.

As the cocoa mass which is to be roasted is fed into the cylinder 1 through the intake aperture 6, it is picked up by the rotating wiper blades 1 2 and distributed as a thin layer over the inside wall of the heated cylinder 1 and is transported in the direction of the separator assembly 8. While this is happening, a more or less large bow wave forms in front of the wiper blades 12, the content of the bow wave being constantly interchanged with that of the thin layer, both the thin layer and also the bow wave being in constant turbulent movement, the result being that no measurable radial temperature gradient oc curs. The temperature sensors 1 3 plunge thereby into the thin layer or the bow wave, supplying thereby a signal analogous with the local temperature in the cocoa mass.While it is present inside the cylinder 1, the cocoa mass is roasted, the roasting gases and water vapour escaping and any hot and/or dry air possibly blown into the intake aperture 7 being entrained. When the end of the heated cylinder is reached, cocoa mass and gas mixture are separated in the separator head 10, which is advantageously so designed that the cocoa compositions can leave the cylinder 1 only in the immediate vicinity of the outlet orifice 16, while the gas mixture (consisting of roasting gases, water vapour and possibly air) can only leave the cylinder 1 in the vicinity of the rotating shaft 11. Any particles of cocoa mass which may be entrained in the gas mixture are thrown outwardly by the centrifugal action of the rotating shaft 11, the outlet orifice 9 being protected by a baffle 1 7 which is part of the separating head 10.The gas mixture leaves the apparatus through the outlet orifice 9, while the roasted cocoa mass leaves the apparatus through the outlet orifice 1 6. The temperature-analogous measuring signals supplied by the measuring sensors 13, converted as already described in the measured value processing and transmitting part 14 which is co-rotating on the shaft 11, are transmitted to the stationary evaluating and control part 1 5 where they are further processed to a temperature profile present in analogue and/or digital form. Via a corresponding link, the converted signals corresponding to the temperature profile are fed into a control unit or a process computer and.

after comparison with a predetermined temperature profile, act on the temperature and/or quantity of the heating medium to be supplied to the individual zones of the heating jacket of the cylinder 1.

Claims (9)

1. A method of manufacturing cocoa mass in which the cocoa beans are processed by drying, husk-removal, crushing, comminution and roasting to produce a roasted cocoa mass, characterised by the following sequence of procedural stages --crushing, preliminary husk removal and preliminary separation of raw cocoa beans, -preliminary drying of the crushed cocoa beans to a moisture content of 4% to 3% at a temperature of 40"C to 90"C, -separation of the crushed kernels from pieces of husk, ---comminution of the crushed kernels and secondary drying to a moisture content of 3% down to 2%, utilising the heat energy released during comminution and at a negative pressure of up to 0.5 atm roasting of the cocoa mass in a thin moving layer and with continuous passage through temperatures of 100'C to 1 40etc, ---cooling of the fully-roasted cocoa mass.

2. Method according to Claim 1, characterised in that preliminary drying is carried out preferably at a temperature of 60"C to 80'C while the secondary drying process is carried out to a moisture content of about 2.5%, the secondary drying temperature being a maximum of 90"C.

3. A roasting apparatus for thin-layer roasting of cocoa mass for carrying out the method according to Claim 1, with a heatable basic body having wiper blades disposed in the interior and rotatable via a shaft, characterised in that p cylindrical heatable basic body (1) is disposed so as to be inclined in a variable position, a plurality of radially adjustable wiper blades (12) are disposed in known manner on a centrally located shaft (11) so as to rotate within the interior of the basic body --on at least one wiper blade (12) there are, at a selectable distance from one another, a plurality of temperature sensors (13) connected by conductor elements to a measured value processing and transmitting part (14) located on the shaft end upstream of the measured value processing and transmitting part (14) but not connected thereto is an evaluating and control part (15) which is connected to a process computer and/or recording and indicating apparatus.

4. A roasting apparatus according to Claim 3, characterised in that the heating means is sectionally controllable and is disposed on the periphery of the basic body.

5. A roasting apparatus according to Claims 3 and 4, characterised in that the temperature sensors (13) on all wiper blades (12) are disposed in a spirally staggered arrangement and are constructed on a semiconductor base.

6. A roasting apparatus according to Claim 1, characterised in that in the measured value processing and transmitting part (14) and in the evaluating and control part (15) there are in each case a transmitter and a receiver for bi-directional signal transmission.

7. A roasting apparatus according to Claims 1 and 6, characterised in that signal transmission takes place on a basis of infrared rays.

8. A method of manufacturing cocoa mass substantially as described in the example disclosed herein.

9. A roasting apparatus as claimed in Claim 3 substantially as herein described with reference to the accompanying drawings.