Patent Application
20090274803
The invention relates to a rapid and simple method for crystallizing (or tempering) real chocolate in the form of stable Beta V polymorph crystals by dispersing seed crystals into a liquid chocolate mass. The invention further relates to a method and system for predicting the optimal temperature of the chocolate at admixing.
Cocoa butter, a major component of chocolate, is a polymorphic product. The fats in cocoa butter can crystallize in six different forms (polymorphous crystallization). Making good chocolate is about forming the most of the type V crystals (Beta. V form). Tempering is therefore an important step in the production of chocolate and chocolate products.
Pre-crystallization of chocolate serves to initialize the crystallization of part of the fat of a chocolate mass into polymorphic forms V and VI (when using the terminology of Wille and Lutton), also called polymorphic forms Beta 2 and Beta 1 (when using the terminology of Larsson). Polymorphic forms V or Beta 2 are further referred to as Beta V crystal forms.
Chocolate users (chocolatiers) should pre-crystallize the chocolate mass before using it. Tempering is a way to induce an appropriate pre-crystallization. Tempering is the process of inducing satisfactory crystal nucleation of the liquid fat in chocolate so that the chocolate forms stable Beta V crystals. The stable crystals function as seeds during further cooling. The liquid chocolate crystallizes around these seeds in the right form.
It is however difficult to obtain Beta V crystals by simply cooling chocolate. Tempering is therefore required.
Tempering is typically a thermal process, and generally involves melting the fat by heating the chocolate mass to typically about 40-50° C. and then slowly cooling it with constant stirring to about 25° C.-27° C. to form nuclei for fat crystal growth (id est to initialize fat crystallization). Then, the chocolate mass is typically reheated about 0.5° C.-4.0° C. with the aim of melting most of the unstable crystals, and of preserving the content of Beta V crystals, which melt at higher temperature than unstable crystals. An amount of about 0.1%-5% (percentage on the total fat contained in chocolate), more typically about 2%-4% of stable crystals is typically preserved in the mass ready for depositing and further use.
To obtain pre-crystallized chocolate, the chocolate mass is typically cooled and scraped on a marble at room temperature of about 18° C.-20° C., or on a cooled scraped surface of a heat exchanging device.
Disadvantages of these classical methods are amongst others the cost of materials and equipments needed to guide and control the temperature, the labor and necessary knowledge (skills) of the user.
In addition to that, with the traditional tempering processes, besides the highly desirable stable Beta V crystals, unavoidably a content of more or less instable crystals is created such as the Alpha (α) and Beta IV crystals.
Recently, attempts have been made for securing a content of only the desirable type of crystals in the mass simply by adding a content of seeding crystals in powder-form into a liquid, temperature controlled chocolate mass.
Such a method is for instance known from DE 10118354 (Sollich). In DE 10118354 thermally treated seed crystals in powder-form are suspended into a branched off chocolate stream in a mixer and then supplied to a mixing stage at the end of a tempering machine, i.e. at a position after the cooling stages. This means that in a first step, the mass is cooled down to a temperature (T) below 37° C., so that at least the desirable high melting stable Beta V crystals survive, before adding of the seed crystals.
Another such method is described in WO 01/06863 whereby seed material consisting of a cooled mixture at a temperature above 30° C. is added to a pre-cooled chocolate mass.
A disadvantage of such methods is that the chocolate mass has to be pre-cooled, which requires an expensive device and means a loss of energy.
U.S. Pat. No. 6,391,356 describes methods to postpone crystallization of the fat phase until final cooling with the aim of minimizing dramatic increases in viscosity typically associated with tempered chocolate. In the methods described in U.S. Pat. No. 6,391,356 melting of the seeding agents is avoided. Specific and expensive equipment is needed, amongst others to pre-cool the chocolate mass before seeding, to maintain a certain processing temperature after seeding, to quickly cool the chocolate after seeding etc.
EP 0 521 205 discloses a continuous tempering method wherein a slurry comprised of seeds (shea stearin crystals) in a liquid fat (cocoa butter) is added to a liquid chocolate mass. The described method is not applicable to batch processes and again requires particular and expensive machinery to keep the slurry at a strictly controlled temperature.
All references cited above are incorporated by reference herein.
It is an aim of the present invention to provide a method and means for the rapid and easy (pre-)crystallization of chocolate into the highly desired stable Beta V crystals.
It is an aim of the present invention to provide a method that does not have the drawbacks of the prior art.
It is a further aim of the invention to provide a method to pre-crystallize at least a part of the fat contained in a chocolate mass so that the final product, the solidified chocolate, will develop no or only a slight amount of white efflorescences (fat bloom) upon prolonged storage.
It is yet another aim of the invention to provide a method for artisanal use.
The present invention relates to a rapid and simple (batch) method to pre-crystallize (temper) a chocolate mass (a real chocolate mass) without any cooling devices such as tempering machines.
The present invention provides for a (batch) method to pre-crystallize real chocolate in the form of Beta V crystals, said method comprising the following (subsequent or concurrent) steps:
determining (identifying) an initial temperature (TCi) for a chocolate mass (to have) before seed crystals are admixed thereto, said TCi exceeding its (the chocolate's) critical temperature,
obtaining a liquid chocolate mass by melting it to this initial temperature (TCi),
dispersing into said liquid chocolate mass at the initial temperature (TCi) solid crystal seeds consisting of at least one ingredient selected from the group consisting of (solid) cocoa butter, a (solid) cocoa butter equivalent and/or (solid) real chocolate, wherein the crystal seeds contain a dominating amount of stable Beta V crystals,
mixing the chocolate mass and the crystal seeds until the seeds are melting, which means that these seeds are completely melted or almost completely melted, and may let a small amount (advantageously between (about) 10% and (about) 0.1%, preferably between (about) 5% and (about)0.5% (w/w)) of crystals not melted and maintained as seeds,
cooling down the thus obtained mixture that is continuously stirred to a pre-crystallization temperature (Tpc), said cooling being achieved through the admixing of the crystal seeds and through heat exchange with the environment to obtain a pre-crystallized chocolate, and
Optionally maintaining the thus obtained mixture at the pre-crystallization temperature to maintain the chocolate mass in a pre-crystallized state.
In a method of the invention, the optimal TCi is determined, id est predetermined, identified, or established in advance (see below), whereafter the chocolate mass to be seeded is simply melted to said temperature. Unlike in many methods of the art, the chocolate mass is thus not melted (heated) and subsequently pre-cooled before seeding.
The desired initial temperature of the chocolate mass (TCi) can be determined (identified, established) experimentally or can be predicted trough modeling.
This temperature TCi varies in function of (a) the type of chocolate, (b) the amount (mass) of chocolate treated, (c) the amount (mass) of crystal seeds added, (d) the temperature of those crystal seeds at admixing, (e) the material (most often plastic or inox (stainless steel)) of which the container (or recipient) is made in which the mixture is cooled, (f) the form or geometry of the container (most often a hemispheric bowl with a given diameter), and (g) the environment in which the container is placed to allow cooling (e.g. ambiant air or a thermostatic water bath at e.g. 32° C.).
The optimal TCi is advantageously determined (identified, established) by modeling the variation of internal energy or heat exchange in the system. Once determined, tables or figures may be prepared which help a person without skill in choosing/determining the correct TCi.
The chocolate mass that is treated preferably is a real chocolate mass prepared by admixing dark chocolate, milk chocolate, household chocolate and/or white chocolate.
Advantageously, the crystal seeds of the invention (also referred to as cocoa butter pieces or CB pieces) have an initial temperature equal to or close to the ambient temperature (Tamb). By <<ambient temperature>> is meant the temperature of the medium (e.g. air) surrounding an object (in casu the chocolate mass). Depending on the environment or medium and the working conditions, the ambient or room temperature may vary between (about) 10° C. and (about) 30° C., yet more typically between (about) 18° C. and (about) 29° C. Most often, the ambient temperature is between (about) 18° C. and (about) 25° C., even more typically between (about) 19° C. and (about) 21° C. By <<close to >> is meant the ambient temperature±1° C. (precision of thermometer). Preferably the CB pieces (crystal seeds of the invention) thus have a TBi of between (about) 10° C. and (about) 30° C., preferably of between (about) 18° C. and (about) 29° C., more preferably of between (about) 18° C. and (about) 25° C., even more typically of between (about) 19° C. and (about) 21° C.
In a method of the invention, <<solid>> crystal seeds according to the invention are added to a chocolate mass at TCi, which means that the crystal seeds are in a solid state or solid form prior to addition to the chocolate mass. Preferred seeding agents are solid cocoa butter seeds. Alternatively (solid) real chocolate and/or (solid) cocoa butter equivalent (Directive 2000/36/EC) such as those based on Illipe, Borneo tallow or Teng kawang, Palm oil, Sal, Shea, Kokum gurgi and/or Mano Kernel may be used as seeding agent.
After addition to the chocolate mass (at TCi) the solid crystal seeds according to the invention start melting into the chocolate mass, as the melting temperature of the seeding material advantageously is below the TCi (see the Examples).
The (batch-wise) adding of the (solid) crystal seeds or CB pieces to the liquid chocolate mass advantageously serves two purposes: they are a cooling source and they help initiate crystallization of the chocolate in the right form (Beta V form). Advantageously no cooling equipments are needed. The recipient in which the mixture (of the chocolate and the CB pieces) is cooling down (is allowed to cool down) may be left to the air or may be placed in a thermostatic bath of e.g. 32° C.
The (batch-wise) addition of solid CB pieces or crystal seeds according to the invention accelerates the cooling of the chocolate to be tempered. As melting is an endothermic process, there is an initial rapid drop in temperature after dispersion of the CB pieces (crystal seeds) into the liquid chocolate mass. The melting of the crystal seeds or CB pieces (e.g. pastilles), slows down as the temperature of the chocolate lowers.
Advantageously CB pieces (crystal seeds according to the invention) are spherical or hemi-spherical in form. Their diameter may vary between (about) 20 and (about) 2 mm, yet preferably they have a diameter of between (about) 10 and (about) 5 mm. Other forms of CB pieces (crystal seeds) may be used, yet beads or (hemi-)spherical particles are most practical for many reasons. A powder may be used yet this may cake.
Preferably between 1% and 20% (w/w % of the chocolate mass to be seeded) of (solid) seed crystals or (solid) CB pieces are dispersed into the liquid chocolate mass. More preferably between 6.5% and 17% (w/w) of seeding agents according to the invention are added.
Most preferably (about) 10% (w/w) of seed crystals (e.g. cocoa butter seeds) are dispersed into the liquid chocolate mass.
Preferably the initial temperature of the chocolate mass before adding the crystals seeds (TCi) is (then) more than 1° C. above the critical temperature. And preferably the pre-crystallization temperature (Tpc) is (then) (about) 0.5° C. to (about) 2° C. below the critical temperature. Advantageously the pre-crystallization temperature is below 37° C., preferably between (about) 30° C. and (about) 35° C., possibly between about 33° C. and about 33.2° C., yet more preferably between (about) 31° C. and (about) 33.5° C., even more preferably between (about) 31° C. and (about) 33° C.
Advantageously the initial temperature TCi of the chocolate mass is chosen (determined) such that a pre-crystallization temperature of below 37° C., preferably of between (about) 30° C. and (about) 35° C., possibly between about 33° C. and about 33.2° C., yet more preferably between (about) 31° C. and (about) 33.5° C., even more preferably between (about) 31° C. and (about) 33° C. is reached within 1 to 10 minutes, more preferably within 3 to 6 minutes, advantageously within 5 to 6 minutes. Said time to reach the Tpc, e.g. 6 minutes, is advantageously set (entered) as a fixed parameter into the modeling. Alternatively, the time needed to reach a pre-crystallization temperature like the above is determined experimentally or is predicted (through modeling).
The pre-crystallization temperature should preserve the crystal seeds initialized by the partial melting of the CB pieces.
For optimal TCi temperatures in case of adding (about) 10% (w/w) solid CB pieces according to the invention, see e.g.
After pre-crystallization the chocolate is typically poured into a mould and put into a refrigerator where it further crystallizes. Chocolate as such tempered may be used amongst others for the making of chocolate bars, pralines, ganaches etc.
The invention further relates to a computer system for modeling temperature changes in a chocolate mass, said system comprising the coding means adapted to model temperature changes in a liquid chocolate mass to which solid crystal seeds containing a dominating amount of stable crystals are (batch-wise) admixed, and this in function of the time, said system further comprising the means to determine the time needed to reach the pre-crystallization temperature, and the means to determine on the basis thereof the preferred initial temperature (TCi) of the chocolate mass (to have at seeding) so that the pre-crystallization temperature can be reached in an acceptable time (e.g. within less than 6 minutes). Advantageously the time for reaching the desired Tpc is fixed or set (in the sense of a fixed parameter or starting condition) at a value between 1 and 10 minutes, preferably at a value between 3 and 6 minutes, most preferably at 5 or 6 minutes.
Another aspect of the invention concerns a computer system for identifying the optimal initial temperature (TCi) of a chocolate mass, said system comprising the coding means adapted to model temperature changes in a liquid chocolate mass to which solid crystal seeds containing a dominating amount of stable crystals are (batch-wise) admixed, and this in function of the time, said system further comprising the means to determine the time needed to reach the pre-crystallization temperature, and the means to determine on the basis thereof the preferred initial temperature (TCi) of the chocolate mass (to have at seeding) so that the pre-crystallization temperature can be reached in an acceptable time (e.g. within less than 6 minutes). Advantageously the time for reaching the desired Tpc is fixed or set (in the sense of a fixed parameter or starting condition) at a value between 1 and 10 minutes, preferably at a value between 3 and 6 minutes, most preferably at 5 or 6 minutes.
Yet another aspect of the invention concerns a computer system for identifying the optimal initial temperature (TCi) of a chocolate mass, said system comprising the coding means adapted to model temperature changes in a liquid chocolate mass to which solid crystal seeds containing a dominating amount of stable beta V crystals have been (batch-wise) admixed, and this in function of the time.
The <<preferred or optimal TCi>> in the context of the invention advantageously is the initial temperature of a chocolate mass needed to reach a pre-crystallization temperature of between (about) 30° C. and (about) 35° C., more preferably of between (about) 31° C. and (about) 33° C. within an acceptable time, e.g. within (about) 1 to (about) 10 minutes, preferably within less than (about) 6 minutes from adding the crystal seeds of the invention to the chocolate mass. Most advantageously the time needed to achieve the pre-crystallization temperature needed is pre-set at 5 or 6 minutes.
Accordingly, another embodiment of the invention concerns a computer system for identifying the optimal initial temperature (TCi) of a chocolate mass, said system comprising the coding means adapted to model temperature changes in a liquid chocolate mass to which solid crystal seeds containing a dominating amount of stable beta V crystals have been (batch-wise) admixed, and this in function of the time, wherein in the model the time for reaching a pre-crystallization temperature (Tpc) of between 30° C. and 35° C., more preferably of between 31° C. and 33° C. is set at a value between 1 and 10 minutes, most preferably at 5 or 6 minutes.
Advantageously the model—in casu the heat exchange model—takes into account the following parameters: (a) the type of chocolate, (b) the amount of chocolate treated, (c) the amount of crystal seeds added, (d) the temperature of those crystal seeds at admixing, (e) the material of which the container or recipient is made in which the mixture is cooled, (f) the form or geometry of this container, and (g) the environment in which the container is placed to allow cooling.
The system of the invention may further comprise means to store a database(s) containing the optimal TCi's, function of the above parameters, and/or the means to generate tables and/or graphs containing this information. Some of the parameters, e.g. form or geometry of the container, temperature of the crystal seeds, ambient temperature, may have to be determined prior to input.
The invention provides for a novel method to (pre-)crystallize a chocolate mass such as a real chocolate mass in the right form (Beta V form).
The method of the invention consists of adding to a liquid chocolate mass CB pieces crystallized in the right form, the Beta V form. The crystal seeds are added to chocolate having an initial temperature TCi.
The TCi is chosen such that when the chocolate reaches a temperature of (about) 30° C.-33° C., the temperature at which stable Beta V crystals are formed, also referred to as the pre-crystallization temperature, some CB pieces (crystallized in the Beta V form) will remain that have not melted and that can seed the chocolate mass. These remaining seeds allow the initiation of crystallization in the right form.
During tempering the mixture of chocolate and CB pieces is manually stirred and allowed to cool in the air, or more rarely in a thermostatic (water) bath (at about 32° C.).
The method of the invention in fact involves only two short steps: (1) the melting of a chocolate mass to a temperature TCi, which exceeds the melting temperature of type VI crystals, in order to melt all six polymorphic crystal forms, and (2) cooling the chocolate to the crystallization point of Beta V crystals (about 30-33° C.) by adding crystal seeds to the liquid chocolate mass and subsequently through heat exchange with the environment (or surroundings). The addition of solid crystal seeds to a liquid chocolate mass significantly accelerates cooling of the chocolate mass.
The method of the invention has several advantages compared to techniques known in the art.
The method of the invention does not require special skills from the user. Tables, figure or charts may be provided to the chocolate user (for possible charts resulting from modeling according to the invention, see the Examples) from which he can easily derive the optimal TCi.
Further, no special or expensive equipments are needed to control and guide the cooling and tempering of a chocolate mass.
The method of the invention is thus simpler to apply than methods in the art wherein seeding crystals as tempering accelerators are added during the setting step of chocolate, which requires a pre-cooling of the chocolate mass to be seeded.
With the method of the invention, the pre-crystallization temperature is reached relatively fast, e.g. within 6 minutes. In classical tempering methods this takes in general about 20 minutes.
Yet a further advantage of the method of the invention is that the desired TCi of the liquid chocolate mass is more or less the same for all types of chocolate (dark, milk, white, household), whereas classical methods require an adaptation of the temperature according to the type of chocolate.
The method of the invention is thus more simple and faster than methods existing in the art to pre-crystallize a real chocolate mass.
By a <<real chocolate>> is meant a chocolate that requires tempering such as dark chocolate, milk chocolate, household chocolate and/or white chocolate as described in the EC directive 2000/36/EC of the European parliament and the council, which relates to cocoa and chocolate products intended for human consumption (directive of 23 Jun. 2000, incorporated by reference herein). Cocoa butter may be replaced in these chocolates by more than 5% of cocoa butter equivalents.
<<Cocoa butter equivalents>> (CBE) are defined as fat compositions having a solid fat content measured at 30° C. with IUPAC method 2.150 a, the fat composition not being subjected to a thermal treatment, that differs at least 8% absolute from the solid fat content measured at the same temperature with IUPAC method 2.150b, the fat composition this time being subjected to a thermal treatment program described in that method.
The CB pieces (the crystal seeds of the invention) are admixed to or dispersed into the chocolate mass by simple techniques such as manual mixing with a supple spatula or mixing with the help of a mixer of e.g. the type Hobart (laminar flow conditions to mimic manual mixing). The mixing will assure the complete or almost complete melting of the CB pieces. However, a small amount of crystals are advantageously maintained in the chocolate mass as seeds.
These CB pieces will seed the chocolate mass and assure its pre-crystallization. When using a tempering method of the invention (about) 10% to (about) 0.1%, more preferably (about) 5% to (about) 0.5% of seeding crystals remain on the total fat contained in the (seeded) chocolate mass.
The crystal seeds or CB pieces according to the invention consist of one or more components or ingredients selected from the list of cocoa butter, cacao butter equivalents and/or real chocolate as defined in the EC directive 2000/36/EC of 23 Jun. 2000 (see above).
The CB pieces (crystal seeds according to the invention) should contain a dominating amount of stable crystals such as the Beta V crystals. Methods to achieve such dominating amount of stable crystals are known in the art. EP 1 425 975 describes one way of obtaining such dominating amount of stable crystals. By a <<dominating amount>> is meant more than 50%, preferably more than 70%, most preferably more than 90%. EP 0 765 606 describes how chocolate mass from a vessel may be subjected to ultrasonic treatment in order to form stable Beta V polymorph crystals. Both references are incorporated by reference herein. CB pieces having a dominant amount of stable crystals are available on the market.
In the present invention the CB pieces (crystal seeds according to the invention) are dispersed into a chocolate mass heated to above the melting temperature of type VI crystals. The initial temperature of the chocolate (t° at admixing or seeding, or TCi) exceeds the critical temperature, preferably by at least 1° C., more preferably by at least 2° C., most preferably by at least 4° C.
In the present application the <<critical temperature>> is the temperature at which all forms of crystalline fat have changed into a molten state. This temperature may be determined by melting a sample (of the chocolate mass) whose fat is in the Beta (β) condition (obtained for example by leaving molten chocolate for at least three days at a temperature of about 22° C.) and to heat it to a temperature X and to maintain it to for one minute at that temperature X. The mass is subsequently cooled to about 23° C. at a rate of about 1° C./min. (while avoiding that the liquid chocolate mass comes into contact with a surface whose temperature is more than about 3° C. lower than that of the chocolate mass), and examined to see whether the Beta (β) or β′ (Beta prime) phase develops. This experiment is carried out mechano-statically.
That temperature X is the critical temperature (Tc) with which after cooling again solid chocolate is obtained whose crystallization phase is substantially β′ (Beta prime).
The melting point of chocolate depends to some extent on the rate of cooling during production. Moreover the melting point is not one single value, because chocolate has a melting range of several degrees (WO 01/06863).
It was found that the pre-crystallization temperature (Tpc) to which the mixture of chocolate and CB pieces is cooled down should be about 0.5° to about 2° C. below the (thus determined) critical temperature (X) of the chocolate mass, at least in the case of adding about 10% w/w of CB pieces.
It was further found that the initial temperature (TCi) of the chocolate mass before adding of the CB pieces should exceed the critical temperature (X) by at least 1° C.
The temperature TCi varies in function of the container used, the chocolate used, the temperature, amount and properties of the CB pieces, the cooling environment. More specifically, the temperature TCi varies in function of the geometrical form of the vessel (also referred to as the container or recipient), the thermal properties of the vessel like the emission (ε) and the exchange of the external surface (wall) and free surface with the ambient air (hex), the quantity of the chocolate mass (MC), the specific heat of the chocolate (Cp), the thermal conductivity of the chocolate (k), the quantity or amount of CB pieces added (MB), the melting kinetics of these CB pieces (dα/dt), the latent heat of these CB pieces (lf), the initial temperature of these CB pieces (TBi), the thermal properties of the environment (k of air (e.g. in the case of plastic container) or water (e.g. in the case of an inox (stainless steel) container placed in a thermostatic water bath)) and the temperature of the environment (Tamb).
The invention will be described in further details in the following examples by reference to the enclosed drawings, which are not in any way intended to limit the scope of the invention as claimed.
In this particular example the optimal TCi was determined through modeling using the FLUENT® Flow Modeling Software. Other suitable software systems exist and are available to the person skilled in the art.
The model serves to reproduce the evolution of the temperature of the chocolate during tempering. To achieve this, one has to start from physical phenomena translated into mathematical formulas.
The energy balance calculated for a portion of the volume (in the x direction in Cartesian coordinates) containing a uniform repartition of the CB pieces in the chocolate mass can be written as:
(ρCp)m∂T/∂t=k∂2T/∂x2−(ρCp)mUx∂T/∂x−Qf [formula I]
wherein (ρ Cp)m ∂T/∂t is the total variation of internal energy in the system; k ∂2T/∂x2 is the variation of internal energy through conduction; (ρ Cp)m Ux ∂T/∂x the variation of internal energy by convection due to agitation; and Qf the shaft item, said shaft item standing for the heat consumed by the melting of the CB pieces in the liquid chocolate mass
and wherein
The losses by convection with the outside (surrounding environment) can be calculated with the law of Newton:
Q
c
=U
ex
A
system(
wherein
During preliminary experiments it became clear that the convection term is sufficiently small to allow the modeling of a manual stirring by introducing an effective thermal conductivity coefficient.
This approach consists in integrating in a single coefficient the action of conduction and convection in the heat exchange balance [formula I]. One considers that convection loss can be expressed as a function proportional to the temperature gradient [see formula II]. This assumption simplifies considerably the numerical simulation.
The aim of this approach is to adjust the thermal conductibility k to a value superior to the real thermal conductivity. If the effective thermal conductivity coefficient, keff, is adjusted to a value above the reel thermal conductivity, the amplification of heat transfers created by the movement of convection induced in a stirred system is taken in consideration.
The evolution of the temperature in the recipient (containing chocolate mass and CB pieces) can thus be rewritten as:
(ρCp)m∂T/∂t=keffΔT−Qf [formula III]
The initial conditions and the conditions at the limits can be calculated as follows: Conditions at limits, at free surface and at the walls of the recipient, take into account a heat transfer term by convection and a heat transfer term by radiation with the environment. The radiation term is function of the emissivity ε of the material of the container used: emissivity ε depends on the nature of the emitting surface (in this case the external wall of the recipient).
The chocolate user typically uses a recipient or container made of plastic or inox (stainless steel). The values of εinox and εplastic can be found in the literature: εinox=0.21 and εplastic=0.93.
When working in air (e.g. in the case a plastic recipient is used) a value for hwall of 4 W/m2K at the wall of the recipient (most often a bowl) and a value for hfree surface of 6.8 W/m2K were used as they were find satisfying. When working au bain marie (e.g. when using an inox (stainless steel) bowl placed in a water bath of e.g. 32° C.), the following values were taken: hwall=125 W/m2K and hfree surface=6.8 W/m2K.
When working in air, T∞=Tamb whereas in water T∞=the water temperature and Tamb the temperature of the ambient air.
The shaft item Qf, regroups the heat consumed during the melting but also takes into account the heating of CB pieces in the solid state and subsequently in the liquid state.
If α (alpha) is the liquid cocoa butter fraction at a given moment during the melting process, then we get:
wherein Vt=Vchocolate+VCB pieces, MBO and MB are respectively the total volume (of the chocolate mass+the CB pieces), the initial mass and the mass at a given moment of the solid CB pieces. Rho (ρ, Kg/m3) is herein the ratio between the instantaneous mass of the solid CB pieces and the total volume Vt.
The melting velocity of the CB pieces can then be calculated as follows:
wherein A0(s−1) is the pre-exponential factor, Ea(kJ/mol) is the energy of activation, R(kJ/mol) the gas constant, T(K) the absolute temperature and n the reaction order. This is an empirical formula based on DSC analyses.
The shaft item in the energy equation is defined as:
Q
f=[the heat requested for heating the solid and liquid CB pieces]+[[melting kinetics]×[latent melting heat]].
For the melting kinetics, see formula IV.
If R is the ratio of the mass of the CB pieces (MB) over the mass of the chocolate (MC) and lf is the latent melting heat of CB pieces (for cocoa butter an lf of 157 000 J/kg is found in literature); and if we assume that the heat used to heat the solid, next liquid CB pieces (e.g. cocoa butter) is negligible, then the heat balance can be written as:
(McCc+MBCB)ΔT=lfMB+MBCB
from which we derive that:
This mathematical model was introduced in the FLUENT® Flow Modeling Software.
The above mathematical model was validated against experimental data.
A bowl with a volume of 1.8 l, with a lower diameter of 10.74 cm and an external diameter of 24.4 cm was used as recipient containing the chocolate mass and the CB pieces. This is a typical example of a recipient used in the art by the chocolate user. A plastic recipient was used for working in air and a stainless steel, more particular an inox (stainless steel) recipient for working in water (a water bath).
The temperature was measured via thermocouples of the T type. The thermocouples were connected to a data logger having 8 channels and registering the temperature every second. The precision of the thermocouples was +0.2° C.
A first thermocouple was placed relatively far from the chocolate surfaces and was measuring the ambient temperature. A second thermocouple measured the temperature of the water bath (in case of a cooling au bain marie). Two thermocouples were submersed into the chocolate mass, at the same depth but at different radial positions. The temperature of the chocolate in each case was determined close to the surface near the extremity of the bowl where the temperature gradient is the highest.
During the tempering process, the chocolate is normally manually stirred to ensure a uniform suspension of the CB pieces (e.g. cocoa butter pastilles) in the chocolate mass. In order to reproduce such manual stirring, a mixer as shown in
The accuracy of the model was tested amongst others for an experiment performed in water. In this experiment 10% (w/w) of cocoa butter pastilles, approximately semi-spherical in form, with a radius of about 2 cm, and of a transparent yellow color were added to a chocolate mass of 2.4 kg of chocolate (in this particular case dark chocolate) so that R=0.1. The initial temperature TCi of the chocolate was 51° C., the initial temperature of the cocoa butter pastilles TBi was 21° C., and the ambient temperature Tamb was 22° C. The recipient used was a metallic bowl that was cooled au bain marie.
These curves further show that the admixing of the solid crystal seeds (the CB pieces) induces a very rapid decline in temperature of the mixture. This is caused by the melting of the CB pieces. According to the model, the drop in temperature continues until the CB pieces are almost completely melted. Thereafter, cooling proceeds through heat exchange with the environment.
In the present example, the initial temperature of the CB pieces (same type as in Example 2) TBi was identical to the ambient temperature (Tamb). The recipient used was hemispheric in form with a radius of 24 cm and made from plastic. The vessel (recipient) was placed in ambient air. Data and predictions were generated for different ambient temperatures.
The modeling allows us to determine the TCi of a chocolate mass needed to reach a pre-crystallization temperature of between 31° C. and 33° C. five (5) minutes after adding of the CB pieces to the chocolate mass.
The data generated can be presented in the form of a graph like
The above shows that the method of the invention is easy, highly reproducible and fast. In the present example, in order to favor the cooling due to the melting of CB pieces and to limit the cooling due to conduction, the recipient or vessel containing the chocolate and CB pieces, was placed in ambient air. The above example demonstrates the applicability of the method of the invention under such working conditions.
However, for the same reasons, it is preferable to use a recipient or vessel made of plastic rather than metal (inox) to limit the loss via radiation.
Pre-crystallization is achieved when the temperature of the chocolate TC, 300 seconds after the addition of 10% of CB pieces to the chocolate mass, is below the critical temperature. Preferably X>TC>X−2° C., wherein X is the critical temperature and TC the temperature of the chocolate at t=300 seconds. After 300 seconds there should be no CB pieces visible with the naked eye.
After melting of the CB pieces and in order to maintain the chocolate mass in a pre-crystallized state, the recipient containing the seeded chocolate mass can be put in a caloporteur fluid (also known as a heat conducting fluid) kept at the pre-crystallization temperature±0.5° C. in a heating device.
The (optimal) Tci was determined for 3 types of chocolate (dark chocolate, milk chocolate and white chocolate) using the mathematical model according to the invention. The parameters were the following:
Plastic bowl with the following dimensions:
Total Height: 10.5 cm
Bottom diameter: 13.2 cm
Upper diameter: 24.8 cm
This vessel was placed in air. The agitation of the chocolate+the cocoa butter pieces was done manually with a plastic spatula, as currently used in the art.
The volume occupied by the chocolate in the bowl varies following the amount of chocolate considered (1 kg, 2 kg or 3 kg). The dimensions used in the mathematical model to calculate the volume are given in the following table:
The <<pre-crystallization>> is defined as the state at which chocolate is in liquid form and contains crystals seeds (for example after cooling with CB drops), i.e. the state at which the chocolate is tempered.
The optimal pre-crystallization temperature (Tpc), where enough crystal seeds are present, was determined experimentally with the help of the Sollich Tempermeter.
The Sollich Tempermeter characterizes the thermal properties of a pre-crystallized chocolate subjected to a controlled cooling regime. This technique measures an inflection point in the cooling curve or traces and uses this data to produce a Temper slope value for the inflection.
Higher Temper slopes values correspond to higher levels of pre-crystallization in chocolate.
The Sollich Tempermeter is typically run using a 10 minutes test period to produce the cooling trace for the tempering determination. If a chocolate does not show an inflection during the 10 minutes run, it would typically be described as having no pre-crystallization.
If a chocolate shows an inflection with a Temper slope value between 4 and 6, it is defined as <<well pre-crystallized>>.
If a chocolate shows an inflection with a Temper slope value lower than 4, it is defined as <<low pre-crystallized>>.
If a chocolate shows an inflection with a Temper slope value higher than 6, it is defined as <<high pre-crystallized>>.
The Temper slope value is measured 6 minutes after the addition of the CB pieces in the system.
The optimal pre-crystallization of the chocolate mass is reached when, 6 minutes after adding of the CB pieces, the temper slope value is between about 4.5 and 5.5, more preferably between 4.8 and 5.2.
The optimal pre-crystallization temperatures (Tpc) correspond therefore to the temperatures of chocolate mass when the optimal pre-crystallization of the chocolate mass is reached 6 minutes after adding of CB pieces. The determined pre-crystallization temperatures (Tpc) are 33.3° C. for dark chocolate, 32.4° C. for milk chocolate and 32.6° C. for white chocolate, were introduced in the mathematical model.
The optimal Tci temperature was calculated by the mathematical model for a series of ambient temperature (from 18° C. to 29° C.) for each quantity of chocolate (1 kg, 2 kg, 3 kg) and for each type of chocolate. This calculation was based on the criterion that the pre-crystallization temperature (Tpc) had to be reached after 6 minutes. The chocolate was then considered as pre-crystallized.
Using these parameters for chocolate masses of 1 kg, 2 kg and 3 kg, the mathematical model gives the following data and graphs (
Therefore, according to the model, if a quantity of CB pieces corresponding to 10% of the quantity of chocolate and having a temperature Tbi identical to ambient temperature (Tamb) is added at the optimal chocolate temperature Tci, the temperature of the mix obtained after 6 minutes of manual agitation with a plastic spatula will be equivalent to the optimal pre-crystallization temperature (Tpc).
The tolerance on the values of optimal temperature Tci (i.e. the variation on Tci acceptable to obtain a well pre-crystallized chocolate after 6 minutes) was measured experimentally in some of the combinations ambient temperature/mass of chocolate.
This was done with the Sollich Tempermeter. Cocoa butter was added to chocolate at different temperatures under and above the calculated Tci. The Temper slope was measured after 6 minutes. When the Temper slope was between 1.0 and 7.0, it was considered that the initial temperature is within the acceptable temperature region.
Under the conditions considered here, tolerance was determined to be Tci+/−0.4° C.
The three following tables give the Tci values and the minimum and maximum acceptable values, for the three types of chocolates at different temperatures (between 18° C. and 29° C.) and for different masses of chocolates (1 kg, 2 kg, 3 kg).
| Number | Date | Country | Kind |
|---|---|---|---|
| 06114338.4 | May 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/054882 | 5/21/2007 | WO | 00 | 10/8/2008 |
