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Comparison of precrystallization of chocolate
Journal of Food Engineering 0 1998 Elsevier PII:
Science
SO260-8774(98)00046-6
35 (1998) 281-297 Limited. All rights reserved Printed in Great Britain 0260-8774198 $19.00 + O.OO
ELSEVIER
Comparison of Precrystallization
of Chocolate
S. Bolliger, B. Breitschuh, M. Stranzinger, & E. J. Windhab*
T. Wagner
Swiss Federal Institute of Technology Zurich (ETH), Institute of Food Science, Laboratory of Food Engineering, CH-8092 Zurich, Switzerland (Received
26 May 1997; accepted 20 February
1998)
ABSTRACT Two continuous processes for the precrystallization of chocolate were investigated. An Aasted temper AMT 250 is compared to a newly developed high shear crystallizer The main features of the high shear crystallizer are the compact design, the improved heat and mass transfer; and the highly efficient homogeneous energy dissipation. Starting from the same chocolate recipes, the differences in precrystallization between the conventional and the high shear crystallization technique are compared. Several analytical methods were used for comparison of the chocolate at process outlet and storage temperatures. In the liquid state, viscosity junction and temper curves were established. The final chocolate bars, after moulding and cooling, were compared by calorimetric and color measurements. The comparison of the two processes shows that with a high shear crystallizer the same chocolate crystallization quality can be achieved at a significantly reduced residence time and lower outlet temperature. Furthermore, the new process can be easily adapted to different chocolate recipes by changing the rotational speed. Due to the improved secondary nucleation in shear Jlow. even lower temper values produce bloom stable chocolates. 0 I998 Elsevier Science Limited. All rights reserved
NOMENCLATURE A a”
Aasted temper Color abscissa in the L*a*b*-color
*To whom correspondence
should be addressed. 281
table
282
S. Bolliger et al.
b*
Color ordinate in the L*a*b*-color table Saturation Saturation before Bloom test Saturation after Bloom test Chocolate temper unit Differential scanning calorimeter Brightness in the L*a*b*-color table Rotational speed of the inner cylinder of the high shear crystallizer
c”:, C *n CTU DSC L* RPM
b-Pm1
S
T Cooling Tin
T O”t T z”“e I T zoneII T zinc K
bath
High shear crystallizer Temperature of the cooling medium Temperature at process inlet [“Cl Temperature at process outlet [“Cl Temperature in zone I of the Aasted temper [“Cl Temperature in zone II of the Aasted temper [“Cl Temperature in zone K of the Aasted temper [“Cl INTRODUCTION
The aim of this project was to compare two different principles of continuous devices for the precrystallization of chocolate. A conventional precrystallization process (Aasted temper AMT 250) and a newly developed high shear crystallizer (ETH Zurich, pilot plant device) were compared. For the same milk chocolate various process experiments were carried out to describe the crystallizer characteristics. Precrystallization is the most important step during the crystallization of chocolates. One aim is to produce a precrystallized mass with a low viscosity. This goal is important in the moulding and coating processes which follow precrystallization. A good tempered* chocolate will exhibit excellent gloss on surfaces as well as good mould release (contraction during cooling). It will provide both the best possible resistance to fat migration and coating softening and general blooming during storage. According to Seguine (1991) a precrystallized chocolate exhibits better flow properties if it has many very small crystals instead of a few larger ones. A fraction of l-3% of the cocoa butter can be crystallized if the seeds are sufficiently small without altering the flow properties appreciably. Conventional precrystallization is done by pumping the liquid chocolate through different tempering zones. In the high shear crystallizer only one zone is required. The principle of high shear crystallization to precrystallize chocolate masses has been investigated by Windhab et al. (1993) and Ziegleder (1993). Windhab and coworkers found that exceeding a shear stress of 0.5 Pa led to typical viscosity functions when gap temperatures of less than 25°C were established (stress controlled cone-plate rheometer). With increasing shear stress, lower viscosities and significantly shorter solidification times were found. By means of calorimetric measurements (DSC) it could also be shown, that related to shear stress higher levels of the fiv-modification could be detected. In another work of Windhab (1987) it was shown that the former results can be transferred to a continuous process setup. *Temper: conventional expression in chocolate manufacturing.
Comparison
of precrystallization
of chocolate
283
The influence of shear on mechanical properties of crystals containing suspensions other than food was investigated by Seidel and Friedrich (1992). The authors could show that the viscosity of the melt of glass ceramic decreases with increasing shear rate because the initial platelets (glimmer crystals) were fragmented by shearing. TEMPER The conventional
DEVICES
precrystallizer (Aasted temper AMT 250)
A conventional industrial Aasted temper AMT 250 (Aasted-Mikroverk, Farum, Danmark) was used for precrystallizing the chocolates investigated. Figure 1 shows a scheme of the Aasted tempering system. The chocolate is pumped through the Aasted temper from the bottom to the top, passing through the ‘cooling zone I’ and the ‘crystallization zone K’ (part of the cooling zone) where nucleation is initialized at cooling temperatures between 16 and 18°C and leaving the reheating ‘zone II‘ with an outlet temperature of 2%31°C. Zones I and II are divided into four disklike zones. Each of these zones (as well as zone K) includes a rotating blade to stir the chocolate (82.6 rpm) and improve heat transfer. The high shear crystallizer Figure 2 illustrates the newly developed high shear crystallizer. The primary nucleation is initialized at the surface of the cooling jacket (temperatures between 1 and
outlet
,
H
stirring blades zone II ( reheating)
zone K ( crystallization) zone I (cooling) inlet
I,
1 Fig. 1. Principle
of the conventional
Aasted temper AMT 250.
284
S. Bolliger et al.
19°C Table 2). Two scraping blades remove nuclei from the wall. The high shear flow (up to -500/s) in the narrow annular gap of the apparatus (5 mm) improves heat and mass transfer as well as secondary nucleation of the fat crystals. Furthermore, it could be shown in basic crystallization experiments carried out in comparable rheometric gaps that besides a remarkable reduction in precrystallization time, or residence time (residence time is between 30 and 100 s for a mass flow rate of lo-30 kg/h), the mechanical energy input in high shear flow influences the
outlet
rotor with scraping
ing jacket
Fig. 2. Principle of the high shear crystallizer.
Parameters Sample A01 A02 A03 A04 A05
TABLE 1 and Process Data Used for the Aasted Temper
,Z& 50.1 50.0 50.1 50.1 50.2
28.7 28.7 28.7 27.5 27.4
TZonsI (“Cl
T,oneK (“Cl
TZoneII
26.5 25.0 25.0 25.0 25.0
16.0 16.0 18.0 16.0 18.0
28.0 28.0 28.0 26.5 26.5
/“Cl
285
Comparison of precrystallizationof chocolate TABLE 2 Process Data for the High Shear Crystallizer Sample
RPM (limin]
sol-100 so4-150 SO5-200 SO6-250 so7-300 SO8-320 so9-350 Sll-451 S12-600 s13-700 s15-100 S16-200 s 17-300 S18-500 s19-100 s21-200 S22-300 S23-400 S24-500
100 150 200 250 300 320 350 451 600 700 100 200 300 500 100 200 300 400 500
[$,
p:;
50.0 49.1 50.1 50.0 50.0 50.2 50.4 50.2 50.2 50.1 50.4 50.1 50.2 50.1 50.4 50.2 50.1 50.0 50.0
28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 27.4 27.4 27.4 27.4 26.4 26.4 26.4 26.4 26.4
Tcooling hath (“Cl
Torque [Nml
19.0 19.0 18.0 16.8 15.6 15.9 15.0 13.0 7.0 1.0 17.0 16.6 15.5 9.6 15.0 15.0 13.7 11.1 7.4
5.5 5.6 6.25 7.75 9.0 8.95 9.2 11.1 14.2 16.1 3.7 6.0 7.8 12.5 4.1 6.4 8.4 10.8 13.0
-Pressure [bar1 -1.6 1.7 1.7 1.7 1.8 1.8 1.9 1.9 2.1 2.3 1.7 1.7 1.7 I.9 1.5 1.7 1.8 I.‘) 1.9
crystal modification distribution of the polymorphous cocoa butter. Due to the flow field in the gap, the dissipated energy from the rotor and the nascent crystallization enthalpy are removed quickly.
ANALYTICAL
METHODS
Temper curve measurements Studies on methods to describe the ‘degree of precrystallization’ of chocolates have been made by many authors (Kleinert, 1973; Motz, 19.57; Vaeck, 1973; Vos, 1965). The goal of all methods is to be aware of the crystallization/storage behaviour of the chocolate as early as possible. For determining the degree of precrystallization of a chocolate, cooling curves were measured in a Tricor tempermeter (Model S05A, APV Baker Limited, Strassbourg, France). The chocolate sample was filled into a PVC cup at process temperature and inserted into a ‘Peltier-controlled’ cooling chamber. During a period of 5 min., the sample was cooled from the process outlet temperature (~26.528.7”C) down to 9°C. The temperature in the centre of the sample was measured and plotted versus time. Interpreting this cooling curve involves determining the slopes at two points of inflection generated by the reheating due to crystallization (Fig. 3). As shown in Fig. 3 the so-called chocolate temper unit (CTU) value is dependent on the temperature at the intersection point of the tangents at the inflection points. According to industrial experience, the CTU-value for conventional ‘well-tempered’ chocolate (optimum precrystallization) is between
286
S. Bolliger et al.
3 and 5. A CTU-value below 2 or above 5 means ‘under-tempered’ (too few crystals) or ‘over-tempered’ (optimum crystal content exceeded), respectively. The slope at the second inflection point is an additional criterion (between -0.6 and + 0.6 = well-tempered, above + 0.6 = under-tempered and below -0.6 = over-tempered). Viscosity measurements The viscosity of the precrystallized chocolate was measured off-line in a shear controlled viscosimeter (Bohlin Visco 88, Bohlin Instruments Inc., Cranbury, NJ). The measuring system was a coaxial cylinder with a cylindrical gap width of 0.7 mm. The outer cylinder was temperature controlled at outlet temperature of the precrystallized chocolate. The viscosity as a function of time at a constant temperature and constant shear rate (18.4 s-‘) was measured to specify the solidification behaviour. The torque (shear stress) was measured every 15 s, using a 12 s delay time and 3 s integration time.
I
I CTU = TCTU -17.2C” +CTU ADJUST Tangent l-Indicator where heat of crystallization is first detected
Tangent 2- Slope is indicator of rate of crystallization (provided as SLOPE result by Tempermeter
TCTU
Time [s] First inflection point
Fig. 3. Definition
Second inflection point
of CTU and slope value.
Comparison
qf precrystallization
of chocolate
287
Bloom-test To characterize the temperature related behaviour of the chocolates during storage, processed chocolate bars (Fig. 4) were tested under defined ‘temperature-sweep’ conditions. Four days after the chocolate had been processed, two bars, stored at 18°C were inserted into a temperature controlled box (Heraeus BK 6160, HeraeusVoetsch GmbH, Balingen, Germany) for 24 h. A four step temperature cycle was carried out consisting of 6 h each at 31, 21, 31 and 21°C. The degree of bloom and/ or color changes, respectively, was assessed using the Chroma Meter CR-300 (Minolta AG, Dietikon, Switzerland). Color L*a*b*-measurements To analyze the ‘color values’, ‘ brightness’ and ‘saturation’, the stored chocolate bars were measured, using an L*a*b*-standard-color-configuration method. Measurements were performed before and after the bloom testing. L* represents the brightness, and the saturation is given by C* =,N”+ h”. The L*a*b* color table is organized according to the a* and b* values, which indicate the abscissa and the ordinate, respectively. The measuring tool was fixed right above
Shear Crystallizer
/cooling chamber (10%) 1
1 demoulding at 18 “C
1
color measurement Bloom Test 31”, 6h/ 21”, 6h/ 31”, 6h/ 21°, 6h color measurement
Fig. 4. Flow sheet of process and analytics.
288
S. Bolliger et al.
the sample. The whole set-up was installed in a room, which was held at a constant temperature of 18°C. Before each new start of the color measurements, the Minolta Analyzer was calibrated with a white plate. Each chocolate bar was measured eight times, two times per bar segment. The eight measured data sets (brightness and saturation) were averaged. DSC Calorimetric measurements were carried out on a differential scanning calorimeter (TA Instruments DSC 2910, TA Instruments GmbH, Alzenau, Germany). The melting curves were determined with a heating rate of 3°C per minute, starting at 15°C and going up to 40°C. The melting enthalpy was calculated from the onset point to the offset point. From all curves, the peak maximum was determined and denoted as the ‘melting point’. Samples were taken directly after cooling, as well as one week and one month after processing. The samples were always taken from the same bar and were transferred from the storage room to the DSC measuring equipment in a tempered vessel. About lo-20 mg of a sample were inserted into an aluminium measuring cup and closed.
CHOCOLATE
PROCESSING
Process scheme After steady state conditions were reached in either one of the tempering machines, controlled by the analytical methods described before (refer to Fig. 4), the chocolate mass (milk chocolate, 28% total fat content) was filled into moulds. Each form contained 14 moulds with defined volume of 14 ccm per mould (76 x 30 mm). To avoid the inclusion of air bubbles and to achieve a homogeneous distribution of the chocolate mass inside the moulds, the chocolate forms were throbbed. Thereafter, the surface was scraped to achieve plane chocolate bottoms and constant sample thickness. After moulding, the chocolate form was placed into a cooling cabinet with a constant temperature of 10°C. After a cooling time of 15 min. (core temperature around 15°C) the chocolate was transferred to a climate chamber with a temperature of 18°C. Inside the climate chamber the chocolate was throbbed out of the forms and stored for further analytical tests. Precrystallization
experiments
Experimental data sets for the Aasted temper
In the Aasted temper, chocolates were precrystallized under different temperatures comparable to those used in industry. Tempering values for good tempered chocolates were available from production lines. The mass flow rate was kept constantly at 167 kg/h and the temperatures in the three zones were adjusted to reach the given temper values. Table 1 shows the parameters used in the Aasted temper.
Comparison of precrystallizationof chocolate Experimental
28Y
data sets for the high shear crystallizer
The first aim of high shear crystallization was to reach the same temper values (CTU and slope) as the Aasted temper, if possible at the same outlet temperature; the mass flow rate was kept constant at 27 kg/h. Since it was not possible to reach the same degree of precrystallization at constant outlet temperatures of 28.7”C, the outlet temperature in the high shear crystallizer was reduced to 27.4”C and 265°C (Table 2). For this purpose the temperature of the cooling jacket had to be decreased. Different parameter settings for rotational speed (shear stress), cooling temperature and mass flow rate (residence time) were chosen for the shear crystallization experiments (refer to Table 2). Rotational speeds from 100 to 700 rpm were considered; 100 rpm was the lowest adjustable revolution number on the pilot plant crystallizer, and 780 rpm the highest possible speed, depending on the viscosity of the chocolates and the related measured torque (torque transducer). The outlet temperature of the high shear crystallizer was chosen so as to achieve the same outlet temperature of the chocolate as the conventional Aasted temper (if possible). Increasing the rotational speed led to an increase of the dissipated energy. Consequently, the temperature of the cooling bath had to be reduced to reach the same outlet temperature. The temperature of the cooling jacket (mean value of the temperature at the inlet and at the outlet of the cooling jacket) was adjusted with a powerful cooling water bath.
RESULTS Due to the influence of the precrystallizers outlet temperature on the analytical results of precrystallized chocolate, the results are grouped according to constant outlet temperature in the following chapters. Temper values of precrystallized chocolate Figures 5-7 show the results of the temper value measurements (CTU and slope) after processing at outlet temperatures of 28.7, 27.4 and 26.4”C, respectively. The chocolate precrystallized in the conventional Aasted temper showed well-tempered (AOl, A04, A05) and slightly over-tempered (A02) CTU and slope values. For the high shear precrystallized chocolate (index S) well-tempered values were reached at lower temperatures (26.4”C), whereas the under-tempered (according to conventional tempering criteria) chocolate at 28.7 and 27.4”C showed no difference in gloss properties and showed no bloom after storage. Using a rotational speed in the range of 100-400 rpm produced comparable results in CTU and slope values. Viscosity measurements Figures 8-10 show the results of the viscosity measurements (viscosity as a function of time at constant shear rate and constant temperature) after precrystallization at an outlet temperature of 28.7, 27.4 and 26.4”C. At the same outlet temperature of 28.7 and 27.4”C, respectively, lower sheared chocolates (1200 rpm) showed reduced viscosity at the beginning of the test than the samples precrystallized in the Aastcd
290
S. Bolliger
et al.
temper; the chocolates precrystallized in the Aasted temper showed a faster crystal growth (increase of viscosity with time) in the viscosimeter. The high shear precrystallized chocolates at 2°C lower outlet temperatures (26.4”C, Fig. 10) were comparable in viscosity to the samples precrystallized in the Aasted temper (Fig. 8). For the high shear precrystallized chocolates, the increase of the rotational speed yielded an increase in viscosity at the beginning of the tests for all outlet temperatures (28.7, 27.4 and 264°C). As expected, a lower outlet temperature of the precrystallized chocolate decreases the time necessary for the system to solidify in the shear gap of the rheometer (Fig. 10). Color measurements for bloom effect characterization All produced chocolates considered showed a steady behaviour during bloom testing and storage. None of the chocolates showed significant bloom after temperature cycling. The chocolate samples were tested for brightness (L*-value) and saturation (c*-value). As shown in Figs 11 and 12, the brightness of the high shear crystallized chocolates is higher than that of conventionally precrystallized chocolates. No significant relationship between outlet temperature and brightness of the chocolates was evident. Figure 11 shows the L*-value that has a maximum peak for samples with
7
54-
1
I Ii
6-
0
0
H E .-c
‘E g = c .-
.AL
3-
‘F; = .-ci
1.5
I 1 .o
05*
4
-1.5 -1 .o () -0.5 0.0
? 0
2-
A
l-
T5
)
o-
-l-2
t -r
> (
Fig. 5. Temper values for chocolate at an outlet temperature of 28.7”C.
Comparison
ofprecrystallization
qf chocolate
291
rotational speeds of 300 rpm. As could be shown independently, a maximum crystal content (up to 2.5%) can be reached, when a certain optimum rotational speed is used in the high shear crystallizer. This is true regardless of the outlet temperature. Differences in L*-values before and after bloom testing showed no significant tendency. From Fig. 13 one can see that the saturation of the high shear precrystallized chocolate and conventionally precrystallized chocolate is similar at different outlet temperatures. According to Fig. 14, which shows the difference in saturation between samples measured before and after bloom testing, a higher rotational speed leads to a lower loss of saturation during bloom testing. DSC measurements The samples were measured 1 h after bar production, as well as 1 week and 1 month later. Table 3 indicates a slight tendency of enthalpy to increase for the samples stored during the first week. The melting peak remains constant. The produced chocolates precrystallized in the high shear crystallizer indicate a similar tendency of enthalpy increase during the first week of storage (Table 4). There is no significant relationship between the production temperature and the melting point or enthalpy of the crystals for conventional or high shear precrystallized chocolates.
71.5
6-
4S3 0 A
3 1.0
5-
0.5
% 0.0 4 l
*-
-0.5
l-
-1 .o
O-l-
-1.5
-2F
9 5
,$
,6’ 5
Fig. 6. Temper values for chocolate at an outlet temperature of 27.4”C.
292
S. Bolliger et al.
DISCUSSION The investigations on the Aasted temper showed that the process could be easily handled and controlled. For a given set of parameters, the process reached a steady state condition. The process was shown to be adjustable by altering the degree of precrystallization. The temper values (CTU and slope) were found to be more influenced by a change of the temperature in the first zone (zone I) than by the other adjustable temperature zones. To achieve a small change in the degree of precrystallization, it is recommended to change the temperature in zone K. The outlet temperature, which depends on the chocolate recipe, had a similar effect on the CTU values as temperature changes in zone I, but causes a steep increase or decrease of the slope. This goes along with the existence of more or less stable crystals. It could be shown that with the high shear crystallizer, chocolates of similar good quality compared to the conventional Aasted temper could be produced (equal CTU and slope conditions). For comparable CTU and slope values, the outlet temnerature of the chocolate was slightlv lower. However, the residence time of the chocolate in the high shear crystalliz& hith a minimum of 30 s is much lower than in the Aasted temper. Compared to the Aasted temper, the high shear crystallizer shows: (1) Significantly kinetics);
reduced
residence
time
(caused
by improved
crystallization
7
‘I
654-
Fig. 7. Temper values for chocolate
at an outlet temperature
of 264°C.
Comparison 20 .
--+--A01 A02 soi-100 --so5200
ofprtmy~tallizution qf’docolate
-SO6-250 .-b---Sil-450 --~(-1---S1 2-600 --p-s73-700
7i 1
L
I
100
1000 Time [s]
Fig. 8. Viscosity as a function
of’time
for chocolates
precrystallized
at 28.7”C.
20
--CA04 A05 515-100 I .- -S16-200 --Sl8-500
7LL-ILL_ 10
100
1000
Time Is]
Fig. 9. Viscosity as a function
of time for chtrcolatcs precrystallized
at 77.4”(‘.
S. Bolliger et al.
294 20
I
s19-100 --s21-200 S22-300 -S23-400 -S24-500
F E .z? UJ 8 ._ > 10'
7.
Fig. 10. Viscosity as a function
of time for chocolates precrystallized
37.5 37.0 36.5 36.0 35.5.
1
’
35.0 34.5. 34.0.
Fig. 11. L*-value before bloom test.
at 26.4”C.
Comparison
of preuystallization
of chocolate
2%
38.0 37.5 37.0
1
36.5 Q) 36.0 1 p 35.5
t
L 35.0 34.5 34.0 33.5 33.0
I i ’
296
S. Bolliger et al.
-0.6 1 +
I
I
.
-0.8
1
L =’
1
-1.o.
I
-1.4. -1.6.
I
I
.
n
I n
Fig. 14. Difference of c*-values (c*” = value after bloom test, c*’ = value before bloom test).
(2) crystallization control by rotational than conventional thermal control).
speed regulation
(reacting
much faster
Due to crystallization control by the rotational speed (dissipation control), the outlet product structure (in terms of crystal content and modification) can be easily adjusted. Under the same precrystallization conditions for both processes, the high shear crystallizer requires a smaller volume to produce the same crystal amount because of the reduced residence time and better heat and mass transfer. Furthermore, there are less product losses and cleaning efforts for the high shear device in the case of product change (-300 ml volume). It was shown that high shear precrystallized chocolate (high shear crystallizer) with even lower CTU and higher slope values (under-tempered in the conventional sense) than the ‘industrial standard’ provided good chocolate quality. This gives an estimate that the lower TABLE 3 DSC Results for Chocolate Precrystallized in the Aasted Temper Code
A01 A02 A04 A05
Melting peak (“Cl production 30.0 29.9 30.3 30.1
Enthalpy
Melting peak
Enthalpy
[J/g/
(“Cl
lJk1
production 19.7 22.4 22.0 22.7
1 week
1 week
30.3 29.6 30.2 30.1
25.3 24.0 27.2 25.5
Melting peak
Enthalpy
1 R:!th
1 month
30.5 30.0 30.0 30.3
IJkl
23.8 24.2 21.7 18.2
291
Comparison of precrystallization of chocolate
TABLE 4 DSC Results for Chocolate Code
sol-100 so4-150 so5200 SO6-250 so7-300 so9-350 s15-100 S16-200 s17-300 s19-100 s21-200 S22-300
Precrystallized
in the High Shear Crystallizer
Melting peak
Enthalpy
Melting peak
Enthalpy
Melting peuk
I”Cl production
IJkl
(“Cl
[Jkl
(“Cl
29.9 29.3 29.7 29.8 29.9 30.0 30.1 30.2 29.8 29.7 29.8 29.8
production
21.2 21.9 20.9 21.1 22.1 22.0 21.3 18.1 22.5 21.6 21.7 21.2
Enthalpy
1JM
I week
1 week
1 month
I month
30.2 30.1 29.9 29.8 29.9 29.9 30.3 29.9 30.2 30.6 30.2 30.9
25.9 24.8 24.8 25.0 25.3 25.4 25.5 23.6 23.5 24.9 22.9 23.9
30.2 29.8 29.8 30.5 29.8 29.6 29.9 30.1
246 24.5 22.5 23.0 24.5 23.2 24.0 .!3.?
30.2 30.1 30.2
24.1 24.1 25.2
total crystal amount at lower CTU values in the high shear crystallizer more (smaller) crystals of the stable /&modification.
contains
ACKNOWLEDGEMENTS The authors gratefully acknowledge Aasted-Mikroverk (Farum, Denmark), APV Baker Limited (Strassbourg, France), Systech S.A. (Fribourg, Switzerland) and Mettler-Toledo (Schweiz) AG (Greifensee, Switzerland) for technical and financial support. U. Glunk, D. Kiechl and A. Wahl from the Food Engineering workshop of
ETH Zurich are especially acknowledged
for their technical advice and support.
REFERENCES Kleinert, J. (1973). Enthalpie-Kurven - Hilfsmittel zur Beurteilung der verarbeitungstechnischen Eigenschaften von Fetten und Fettmischungen. Rev. Irzt. Choc., 28(3), 54-69. Motz, R. J. (1957). Die Messung des Temperiergrades von Schokolade. Rev. Int. Choc., 12, 470-476. Seguine, E. S. (1991). Tempering-the inside story. Manufuct. Confectioner, May, 117-125. Seidel, T. & Friedrich, C. (1992). Influence of shear rate and temperature on the crystallization of spontaneous crystallizing glass-ceramic. J. Mater: Sci., 27, 263-269. Vaeck, S. V. (1973). Uber Enthalpie und Erstarrungskurven von Kakaobutter. Rw! Int. Choc., 28( lo), 257-258. Vos, H. J. (1965). Bestimmung der Erstarrungskurven von Fetten mit Hilfe des ShukoffApparates. Fette, Seifen,,,Anstrichmittel, 67(2), 69-72. Windhab, E. J. (1987). Uber die rheologischen Eigenschaften vorkristallisierter Schokoladenmassen, Zentralfachschule der deutschen Stisswarenwirtschaft. Windhab, E. J., Niediek, E. A. & Rolfes, L. (1993). Tieftemperatur-Scherkristallisationneue Aspekte der Temperiertechnik. Siisswaren, 3, 32-37. Ziegleder, G. (1993). Vorkristallisation von Schokoladen-Einfltisse durch Produkt und Maschine. Siisswaren, 1-2, 54-58.
Science
SO260-8774(98)00046-6
35 (1998) 281-297 Limited. All rights reserved Printed in Great Britain 0260-8774198 $19.00 + O.OO
ELSEVIER
Comparison of Precrystallization
of Chocolate
S. Bolliger, B. Breitschuh, M. Stranzinger, & E. J. Windhab*
T. Wagner
Swiss Federal Institute of Technology Zurich (ETH), Institute of Food Science, Laboratory of Food Engineering, CH-8092 Zurich, Switzerland (Received
26 May 1997; accepted 20 February
1998)
ABSTRACT Two continuous processes for the precrystallization of chocolate were investigated. An Aasted temper AMT 250 is compared to a newly developed high shear crystallizer The main features of the high shear crystallizer are the compact design, the improved heat and mass transfer; and the highly efficient homogeneous energy dissipation. Starting from the same chocolate recipes, the differences in precrystallization between the conventional and the high shear crystallization technique are compared. Several analytical methods were used for comparison of the chocolate at process outlet and storage temperatures. In the liquid state, viscosity junction and temper curves were established. The final chocolate bars, after moulding and cooling, were compared by calorimetric and color measurements. The comparison of the two processes shows that with a high shear crystallizer the same chocolate crystallization quality can be achieved at a significantly reduced residence time and lower outlet temperature. Furthermore, the new process can be easily adapted to different chocolate recipes by changing the rotational speed. Due to the improved secondary nucleation in shear Jlow. even lower temper values produce bloom stable chocolates. 0 I998 Elsevier Science Limited. All rights reserved
NOMENCLATURE A a”
Aasted temper Color abscissa in the L*a*b*-color
*To whom correspondence
should be addressed. 281
table
282
S. Bolliger et al.
b*
Color ordinate in the L*a*b*-color table Saturation Saturation before Bloom test Saturation after Bloom test Chocolate temper unit Differential scanning calorimeter Brightness in the L*a*b*-color table Rotational speed of the inner cylinder of the high shear crystallizer
c”:, C *n CTU DSC L* RPM
b-Pm1
S
T Cooling Tin
T O”t T z”“e I T zoneII T zinc K
bath
High shear crystallizer Temperature of the cooling medium Temperature at process inlet [“Cl Temperature at process outlet [“Cl Temperature in zone I of the Aasted temper [“Cl Temperature in zone II of the Aasted temper [“Cl Temperature in zone K of the Aasted temper [“Cl INTRODUCTION
The aim of this project was to compare two different principles of continuous devices for the precrystallization of chocolate. A conventional precrystallization process (Aasted temper AMT 250) and a newly developed high shear crystallizer (ETH Zurich, pilot plant device) were compared. For the same milk chocolate various process experiments were carried out to describe the crystallizer characteristics. Precrystallization is the most important step during the crystallization of chocolates. One aim is to produce a precrystallized mass with a low viscosity. This goal is important in the moulding and coating processes which follow precrystallization. A good tempered* chocolate will exhibit excellent gloss on surfaces as well as good mould release (contraction during cooling). It will provide both the best possible resistance to fat migration and coating softening and general blooming during storage. According to Seguine (1991) a precrystallized chocolate exhibits better flow properties if it has many very small crystals instead of a few larger ones. A fraction of l-3% of the cocoa butter can be crystallized if the seeds are sufficiently small without altering the flow properties appreciably. Conventional precrystallization is done by pumping the liquid chocolate through different tempering zones. In the high shear crystallizer only one zone is required. The principle of high shear crystallization to precrystallize chocolate masses has been investigated by Windhab et al. (1993) and Ziegleder (1993). Windhab and coworkers found that exceeding a shear stress of 0.5 Pa led to typical viscosity functions when gap temperatures of less than 25°C were established (stress controlled cone-plate rheometer). With increasing shear stress, lower viscosities and significantly shorter solidification times were found. By means of calorimetric measurements (DSC) it could also be shown, that related to shear stress higher levels of the fiv-modification could be detected. In another work of Windhab (1987) it was shown that the former results can be transferred to a continuous process setup. *Temper: conventional expression in chocolate manufacturing.
Comparison
of precrystallization
of chocolate
283
The influence of shear on mechanical properties of crystals containing suspensions other than food was investigated by Seidel and Friedrich (1992). The authors could show that the viscosity of the melt of glass ceramic decreases with increasing shear rate because the initial platelets (glimmer crystals) were fragmented by shearing. TEMPER The conventional
DEVICES
precrystallizer (Aasted temper AMT 250)
A conventional industrial Aasted temper AMT 250 (Aasted-Mikroverk, Farum, Danmark) was used for precrystallizing the chocolates investigated. Figure 1 shows a scheme of the Aasted tempering system. The chocolate is pumped through the Aasted temper from the bottom to the top, passing through the ‘cooling zone I’ and the ‘crystallization zone K’ (part of the cooling zone) where nucleation is initialized at cooling temperatures between 16 and 18°C and leaving the reheating ‘zone II‘ with an outlet temperature of 2%31°C. Zones I and II are divided into four disklike zones. Each of these zones (as well as zone K) includes a rotating blade to stir the chocolate (82.6 rpm) and improve heat transfer. The high shear crystallizer Figure 2 illustrates the newly developed high shear crystallizer. The primary nucleation is initialized at the surface of the cooling jacket (temperatures between 1 and
outlet
,
H
stirring blades zone II ( reheating)
zone K ( crystallization) zone I (cooling) inlet
I,
1 Fig. 1. Principle
of the conventional
Aasted temper AMT 250.
284
S. Bolliger et al.
19°C Table 2). Two scraping blades remove nuclei from the wall. The high shear flow (up to -500/s) in the narrow annular gap of the apparatus (5 mm) improves heat and mass transfer as well as secondary nucleation of the fat crystals. Furthermore, it could be shown in basic crystallization experiments carried out in comparable rheometric gaps that besides a remarkable reduction in precrystallization time, or residence time (residence time is between 30 and 100 s for a mass flow rate of lo-30 kg/h), the mechanical energy input in high shear flow influences the
outlet
rotor with scraping
ing jacket
Fig. 2. Principle of the high shear crystallizer.
Parameters Sample A01 A02 A03 A04 A05
TABLE 1 and Process Data Used for the Aasted Temper
,Z& 50.1 50.0 50.1 50.1 50.2
28.7 28.7 28.7 27.5 27.4
TZonsI (“Cl
T,oneK (“Cl
TZoneII
26.5 25.0 25.0 25.0 25.0
16.0 16.0 18.0 16.0 18.0
28.0 28.0 28.0 26.5 26.5
/“Cl
285
Comparison of precrystallizationof chocolate TABLE 2 Process Data for the High Shear Crystallizer Sample
RPM (limin]
sol-100 so4-150 SO5-200 SO6-250 so7-300 SO8-320 so9-350 Sll-451 S12-600 s13-700 s15-100 S16-200 s 17-300 S18-500 s19-100 s21-200 S22-300 S23-400 S24-500
100 150 200 250 300 320 350 451 600 700 100 200 300 500 100 200 300 400 500
[$,
p:;
50.0 49.1 50.1 50.0 50.0 50.2 50.4 50.2 50.2 50.1 50.4 50.1 50.2 50.1 50.4 50.2 50.1 50.0 50.0
28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 28.7 27.4 27.4 27.4 27.4 26.4 26.4 26.4 26.4 26.4
Tcooling hath (“Cl
Torque [Nml
19.0 19.0 18.0 16.8 15.6 15.9 15.0 13.0 7.0 1.0 17.0 16.6 15.5 9.6 15.0 15.0 13.7 11.1 7.4
5.5 5.6 6.25 7.75 9.0 8.95 9.2 11.1 14.2 16.1 3.7 6.0 7.8 12.5 4.1 6.4 8.4 10.8 13.0
-Pressure [bar1 -1.6 1.7 1.7 1.7 1.8 1.8 1.9 1.9 2.1 2.3 1.7 1.7 1.7 I.9 1.5 1.7 1.8 I.‘) 1.9
crystal modification distribution of the polymorphous cocoa butter. Due to the flow field in the gap, the dissipated energy from the rotor and the nascent crystallization enthalpy are removed quickly.
ANALYTICAL
METHODS
Temper curve measurements Studies on methods to describe the ‘degree of precrystallization’ of chocolates have been made by many authors (Kleinert, 1973; Motz, 19.57; Vaeck, 1973; Vos, 1965). The goal of all methods is to be aware of the crystallization/storage behaviour of the chocolate as early as possible. For determining the degree of precrystallization of a chocolate, cooling curves were measured in a Tricor tempermeter (Model S05A, APV Baker Limited, Strassbourg, France). The chocolate sample was filled into a PVC cup at process temperature and inserted into a ‘Peltier-controlled’ cooling chamber. During a period of 5 min., the sample was cooled from the process outlet temperature (~26.528.7”C) down to 9°C. The temperature in the centre of the sample was measured and plotted versus time. Interpreting this cooling curve involves determining the slopes at two points of inflection generated by the reheating due to crystallization (Fig. 3). As shown in Fig. 3 the so-called chocolate temper unit (CTU) value is dependent on the temperature at the intersection point of the tangents at the inflection points. According to industrial experience, the CTU-value for conventional ‘well-tempered’ chocolate (optimum precrystallization) is between
286
S. Bolliger et al.
3 and 5. A CTU-value below 2 or above 5 means ‘under-tempered’ (too few crystals) or ‘over-tempered’ (optimum crystal content exceeded), respectively. The slope at the second inflection point is an additional criterion (between -0.6 and + 0.6 = well-tempered, above + 0.6 = under-tempered and below -0.6 = over-tempered). Viscosity measurements The viscosity of the precrystallized chocolate was measured off-line in a shear controlled viscosimeter (Bohlin Visco 88, Bohlin Instruments Inc., Cranbury, NJ). The measuring system was a coaxial cylinder with a cylindrical gap width of 0.7 mm. The outer cylinder was temperature controlled at outlet temperature of the precrystallized chocolate. The viscosity as a function of time at a constant temperature and constant shear rate (18.4 s-‘) was measured to specify the solidification behaviour. The torque (shear stress) was measured every 15 s, using a 12 s delay time and 3 s integration time.
I
I CTU = TCTU -17.2C” +CTU ADJUST Tangent l-Indicator where heat of crystallization is first detected
Tangent 2- Slope is indicator of rate of crystallization (provided as SLOPE result by Tempermeter
TCTU
Time [s] First inflection point
Fig. 3. Definition
Second inflection point
of CTU and slope value.
Comparison
qf precrystallization
of chocolate
287
Bloom-test To characterize the temperature related behaviour of the chocolates during storage, processed chocolate bars (Fig. 4) were tested under defined ‘temperature-sweep’ conditions. Four days after the chocolate had been processed, two bars, stored at 18°C were inserted into a temperature controlled box (Heraeus BK 6160, HeraeusVoetsch GmbH, Balingen, Germany) for 24 h. A four step temperature cycle was carried out consisting of 6 h each at 31, 21, 31 and 21°C. The degree of bloom and/ or color changes, respectively, was assessed using the Chroma Meter CR-300 (Minolta AG, Dietikon, Switzerland). Color L*a*b*-measurements To analyze the ‘color values’, ‘ brightness’ and ‘saturation’, the stored chocolate bars were measured, using an L*a*b*-standard-color-configuration method. Measurements were performed before and after the bloom testing. L* represents the brightness, and the saturation is given by C* =,N”+ h”. The L*a*b* color table is organized according to the a* and b* values, which indicate the abscissa and the ordinate, respectively. The measuring tool was fixed right above
Shear Crystallizer
/cooling chamber (10%) 1
1 demoulding at 18 “C
1
color measurement Bloom Test 31”, 6h/ 21”, 6h/ 31”, 6h/ 21°, 6h color measurement
Fig. 4. Flow sheet of process and analytics.
288
S. Bolliger et al.
the sample. The whole set-up was installed in a room, which was held at a constant temperature of 18°C. Before each new start of the color measurements, the Minolta Analyzer was calibrated with a white plate. Each chocolate bar was measured eight times, two times per bar segment. The eight measured data sets (brightness and saturation) were averaged. DSC Calorimetric measurements were carried out on a differential scanning calorimeter (TA Instruments DSC 2910, TA Instruments GmbH, Alzenau, Germany). The melting curves were determined with a heating rate of 3°C per minute, starting at 15°C and going up to 40°C. The melting enthalpy was calculated from the onset point to the offset point. From all curves, the peak maximum was determined and denoted as the ‘melting point’. Samples were taken directly after cooling, as well as one week and one month after processing. The samples were always taken from the same bar and were transferred from the storage room to the DSC measuring equipment in a tempered vessel. About lo-20 mg of a sample were inserted into an aluminium measuring cup and closed.
CHOCOLATE
PROCESSING
Process scheme After steady state conditions were reached in either one of the tempering machines, controlled by the analytical methods described before (refer to Fig. 4), the chocolate mass (milk chocolate, 28% total fat content) was filled into moulds. Each form contained 14 moulds with defined volume of 14 ccm per mould (76 x 30 mm). To avoid the inclusion of air bubbles and to achieve a homogeneous distribution of the chocolate mass inside the moulds, the chocolate forms were throbbed. Thereafter, the surface was scraped to achieve plane chocolate bottoms and constant sample thickness. After moulding, the chocolate form was placed into a cooling cabinet with a constant temperature of 10°C. After a cooling time of 15 min. (core temperature around 15°C) the chocolate was transferred to a climate chamber with a temperature of 18°C. Inside the climate chamber the chocolate was throbbed out of the forms and stored for further analytical tests. Precrystallization
experiments
Experimental data sets for the Aasted temper
In the Aasted temper, chocolates were precrystallized under different temperatures comparable to those used in industry. Tempering values for good tempered chocolates were available from production lines. The mass flow rate was kept constantly at 167 kg/h and the temperatures in the three zones were adjusted to reach the given temper values. Table 1 shows the parameters used in the Aasted temper.
Comparison of precrystallizationof chocolate Experimental
28Y
data sets for the high shear crystallizer
The first aim of high shear crystallization was to reach the same temper values (CTU and slope) as the Aasted temper, if possible at the same outlet temperature; the mass flow rate was kept constant at 27 kg/h. Since it was not possible to reach the same degree of precrystallization at constant outlet temperatures of 28.7”C, the outlet temperature in the high shear crystallizer was reduced to 27.4”C and 265°C (Table 2). For this purpose the temperature of the cooling jacket had to be decreased. Different parameter settings for rotational speed (shear stress), cooling temperature and mass flow rate (residence time) were chosen for the shear crystallization experiments (refer to Table 2). Rotational speeds from 100 to 700 rpm were considered; 100 rpm was the lowest adjustable revolution number on the pilot plant crystallizer, and 780 rpm the highest possible speed, depending on the viscosity of the chocolates and the related measured torque (torque transducer). The outlet temperature of the high shear crystallizer was chosen so as to achieve the same outlet temperature of the chocolate as the conventional Aasted temper (if possible). Increasing the rotational speed led to an increase of the dissipated energy. Consequently, the temperature of the cooling bath had to be reduced to reach the same outlet temperature. The temperature of the cooling jacket (mean value of the temperature at the inlet and at the outlet of the cooling jacket) was adjusted with a powerful cooling water bath.
RESULTS Due to the influence of the precrystallizers outlet temperature on the analytical results of precrystallized chocolate, the results are grouped according to constant outlet temperature in the following chapters. Temper values of precrystallized chocolate Figures 5-7 show the results of the temper value measurements (CTU and slope) after processing at outlet temperatures of 28.7, 27.4 and 26.4”C, respectively. The chocolate precrystallized in the conventional Aasted temper showed well-tempered (AOl, A04, A05) and slightly over-tempered (A02) CTU and slope values. For the high shear precrystallized chocolate (index S) well-tempered values were reached at lower temperatures (26.4”C), whereas the under-tempered (according to conventional tempering criteria) chocolate at 28.7 and 27.4”C showed no difference in gloss properties and showed no bloom after storage. Using a rotational speed in the range of 100-400 rpm produced comparable results in CTU and slope values. Viscosity measurements Figures 8-10 show the results of the viscosity measurements (viscosity as a function of time at constant shear rate and constant temperature) after precrystallization at an outlet temperature of 28.7, 27.4 and 26.4”C. At the same outlet temperature of 28.7 and 27.4”C, respectively, lower sheared chocolates (1200 rpm) showed reduced viscosity at the beginning of the test than the samples precrystallized in the Aastcd
290
S. Bolliger
et al.
temper; the chocolates precrystallized in the Aasted temper showed a faster crystal growth (increase of viscosity with time) in the viscosimeter. The high shear precrystallized chocolates at 2°C lower outlet temperatures (26.4”C, Fig. 10) were comparable in viscosity to the samples precrystallized in the Aasted temper (Fig. 8). For the high shear precrystallized chocolates, the increase of the rotational speed yielded an increase in viscosity at the beginning of the tests for all outlet temperatures (28.7, 27.4 and 264°C). As expected, a lower outlet temperature of the precrystallized chocolate decreases the time necessary for the system to solidify in the shear gap of the rheometer (Fig. 10). Color measurements for bloom effect characterization All produced chocolates considered showed a steady behaviour during bloom testing and storage. None of the chocolates showed significant bloom after temperature cycling. The chocolate samples were tested for brightness (L*-value) and saturation (c*-value). As shown in Figs 11 and 12, the brightness of the high shear crystallized chocolates is higher than that of conventionally precrystallized chocolates. No significant relationship between outlet temperature and brightness of the chocolates was evident. Figure 11 shows the L*-value that has a maximum peak for samples with
7
54-
1
I Ii
6-
0
0
H E .-c
‘E g = c .-
.AL
3-
‘F; = .-ci
1.5
I 1 .o
05*
4
-1.5 -1 .o () -0.5 0.0
? 0
2-
A
l-
T5
)
o-
-l-2
t -r
> (
Fig. 5. Temper values for chocolate at an outlet temperature of 28.7”C.
Comparison
ofprecrystallization
qf chocolate
291
rotational speeds of 300 rpm. As could be shown independently, a maximum crystal content (up to 2.5%) can be reached, when a certain optimum rotational speed is used in the high shear crystallizer. This is true regardless of the outlet temperature. Differences in L*-values before and after bloom testing showed no significant tendency. From Fig. 13 one can see that the saturation of the high shear precrystallized chocolate and conventionally precrystallized chocolate is similar at different outlet temperatures. According to Fig. 14, which shows the difference in saturation between samples measured before and after bloom testing, a higher rotational speed leads to a lower loss of saturation during bloom testing. DSC measurements The samples were measured 1 h after bar production, as well as 1 week and 1 month later. Table 3 indicates a slight tendency of enthalpy to increase for the samples stored during the first week. The melting peak remains constant. The produced chocolates precrystallized in the high shear crystallizer indicate a similar tendency of enthalpy increase during the first week of storage (Table 4). There is no significant relationship between the production temperature and the melting point or enthalpy of the crystals for conventional or high shear precrystallized chocolates.
71.5
6-
4S3 0 A
3 1.0
5-
0.5
% 0.0 4 l
*-
-0.5
l-
-1 .o
O-l-
-1.5
-2F
9 5
,$
,6’ 5
Fig. 6. Temper values for chocolate at an outlet temperature of 27.4”C.
292
S. Bolliger et al.
DISCUSSION The investigations on the Aasted temper showed that the process could be easily handled and controlled. For a given set of parameters, the process reached a steady state condition. The process was shown to be adjustable by altering the degree of precrystallization. The temper values (CTU and slope) were found to be more influenced by a change of the temperature in the first zone (zone I) than by the other adjustable temperature zones. To achieve a small change in the degree of precrystallization, it is recommended to change the temperature in zone K. The outlet temperature, which depends on the chocolate recipe, had a similar effect on the CTU values as temperature changes in zone I, but causes a steep increase or decrease of the slope. This goes along with the existence of more or less stable crystals. It could be shown that with the high shear crystallizer, chocolates of similar good quality compared to the conventional Aasted temper could be produced (equal CTU and slope conditions). For comparable CTU and slope values, the outlet temnerature of the chocolate was slightlv lower. However, the residence time of the chocolate in the high shear crystalliz& hith a minimum of 30 s is much lower than in the Aasted temper. Compared to the Aasted temper, the high shear crystallizer shows: (1) Significantly kinetics);
reduced
residence
time
(caused
by improved
crystallization
7
‘I
654-
Fig. 7. Temper values for chocolate
at an outlet temperature
of 264°C.
Comparison 20 .
--+--A01 A02 soi-100 --so5200
ofprtmy~tallizution qf’docolate
-SO6-250 .-b---Sil-450 --~(-1---S1 2-600 --p-s73-700
7i 1
L
I
100
1000 Time [s]
Fig. 8. Viscosity as a function
of’time
for chocolates
precrystallized
at 28.7”C.
20
--CA04 A05 515-100 I .- -S16-200 --Sl8-500
7LL-ILL_ 10
100
1000
Time Is]
Fig. 9. Viscosity as a function
of time for chtrcolatcs precrystallized
at 77.4”(‘.
S. Bolliger et al.
294 20
I
s19-100 --s21-200 S22-300 -S23-400 -S24-500
F E .z? UJ 8 ._ > 10'
7.
Fig. 10. Viscosity as a function
of time for chocolates precrystallized
37.5 37.0 36.5 36.0 35.5.
1
’
35.0 34.5. 34.0.
Fig. 11. L*-value before bloom test.
at 26.4”C.
Comparison
of preuystallization
of chocolate
2%
38.0 37.5 37.0
1
36.5 Q) 36.0 1 p 35.5
t
L 35.0 34.5 34.0 33.5 33.0
I i ’
296
S. Bolliger et al.
-0.6 1 +
I
I
.
-0.8
1
L =’
1
-1.o.
I
-1.4. -1.6.
I
I
.
n
I n
Fig. 14. Difference of c*-values (c*” = value after bloom test, c*’ = value before bloom test).
(2) crystallization control by rotational than conventional thermal control).
speed regulation
(reacting
much faster
Due to crystallization control by the rotational speed (dissipation control), the outlet product structure (in terms of crystal content and modification) can be easily adjusted. Under the same precrystallization conditions for both processes, the high shear crystallizer requires a smaller volume to produce the same crystal amount because of the reduced residence time and better heat and mass transfer. Furthermore, there are less product losses and cleaning efforts for the high shear device in the case of product change (-300 ml volume). It was shown that high shear precrystallized chocolate (high shear crystallizer) with even lower CTU and higher slope values (under-tempered in the conventional sense) than the ‘industrial standard’ provided good chocolate quality. This gives an estimate that the lower TABLE 3 DSC Results for Chocolate Precrystallized in the Aasted Temper Code
A01 A02 A04 A05
Melting peak (“Cl production 30.0 29.9 30.3 30.1
Enthalpy
Melting peak
Enthalpy
[J/g/
(“Cl
lJk1
production 19.7 22.4 22.0 22.7
1 week
1 week
30.3 29.6 30.2 30.1
25.3 24.0 27.2 25.5
Melting peak
Enthalpy
1 R:!th
1 month
30.5 30.0 30.0 30.3
IJkl
23.8 24.2 21.7 18.2
291
Comparison of precrystallization of chocolate
TABLE 4 DSC Results for Chocolate Code
sol-100 so4-150 so5200 SO6-250 so7-300 so9-350 s15-100 S16-200 s17-300 s19-100 s21-200 S22-300
Precrystallized
in the High Shear Crystallizer
Melting peak
Enthalpy
Melting peak
Enthalpy
Melting peuk
I”Cl production
IJkl
(“Cl
[Jkl
(“Cl
29.9 29.3 29.7 29.8 29.9 30.0 30.1 30.2 29.8 29.7 29.8 29.8
production
21.2 21.9 20.9 21.1 22.1 22.0 21.3 18.1 22.5 21.6 21.7 21.2
Enthalpy
1JM
I week
1 week
1 month
I month
30.2 30.1 29.9 29.8 29.9 29.9 30.3 29.9 30.2 30.6 30.2 30.9
25.9 24.8 24.8 25.0 25.3 25.4 25.5 23.6 23.5 24.9 22.9 23.9
30.2 29.8 29.8 30.5 29.8 29.6 29.9 30.1
246 24.5 22.5 23.0 24.5 23.2 24.0 .!3.?
30.2 30.1 30.2
24.1 24.1 25.2
total crystal amount at lower CTU values in the high shear crystallizer more (smaller) crystals of the stable /&modification.
contains
ACKNOWLEDGEMENTS The authors gratefully acknowledge Aasted-Mikroverk (Farum, Denmark), APV Baker Limited (Strassbourg, France), Systech S.A. (Fribourg, Switzerland) and Mettler-Toledo (Schweiz) AG (Greifensee, Switzerland) for technical and financial support. U. Glunk, D. Kiechl and A. Wahl from the Food Engineering workshop of
ETH Zurich are especially acknowledged
for their technical advice and support.
REFERENCES Kleinert, J. (1973). Enthalpie-Kurven - Hilfsmittel zur Beurteilung der verarbeitungstechnischen Eigenschaften von Fetten und Fettmischungen. Rev. Irzt. Choc., 28(3), 54-69. Motz, R. J. (1957). Die Messung des Temperiergrades von Schokolade. Rev. Int. Choc., 12, 470-476. Seguine, E. S. (1991). Tempering-the inside story. Manufuct. Confectioner, May, 117-125. Seidel, T. & Friedrich, C. (1992). Influence of shear rate and temperature on the crystallization of spontaneous crystallizing glass-ceramic. J. Mater: Sci., 27, 263-269. Vaeck, S. V. (1973). Uber Enthalpie und Erstarrungskurven von Kakaobutter. Rw! Int. Choc., 28( lo), 257-258. Vos, H. J. (1965). Bestimmung der Erstarrungskurven von Fetten mit Hilfe des ShukoffApparates. Fette, Seifen,,,Anstrichmittel, 67(2), 69-72. Windhab, E. J. (1987). Uber die rheologischen Eigenschaften vorkristallisierter Schokoladenmassen, Zentralfachschule der deutschen Stisswarenwirtschaft. Windhab, E. J., Niediek, E. A. & Rolfes, L. (1993). Tieftemperatur-Scherkristallisationneue Aspekte der Temperiertechnik. Siisswaren, 3, 32-37. Ziegleder, G. (1993). Vorkristallisation von Schokoladen-Einfltisse durch Produkt und Maschine. Siisswaren, 1-2, 54-58.