Beat Migration Bloom on Chocolate Products by Optimizing Your Process Reprint from The Manufacturing Confectioner May 2010
Beat Migration Bloom by Optimizing Your Process A new look at the tempering process to reduce migration bloom in chocolate products. Bjarne Juul AAK
ntensive research has shown a significant
correlation between process parameters and
Cocoa butter and cocoa butter equivalents
the speed of migration bloom development.
(cbes) are polymorphic fats (Figure 1). Their
It seems that the temperature used for most
solid stability increases with increasing melt-
temper tests in the world is too low and actually
ing temperature, but Form V is actually stable
guides chocolate manufacturers to produce
enough in practice for chocolate production
slightly undertempered chocolate.
and is easy to make and has a perfect melting
The cooling of chocolate and particularly
chocolate shells is too severe, causing too high
Chocolate prefers to crystallize in Forms III
cooling rates, which probably affect the ratio of
and IV, but by using tempering equipment to
Form IV and Form V polymorphs in the final
make the right combination of time, shear and
cooling conditions for a certain fat phase com-
The subsequent transformation, from Form
position, it is possible to make seeds in Form V
IV to Form V, accelerated by the migrating oils
in a partly melted chocolate dispersion.
from fillings, speeds up the bloom-develop-
Different types of tempering equipment or
seed techniques have been developed.
It is found that if this transformation takes
Polymorphs of Cocoa Butter
place at a temperature above room temperature, a type of heat treatment or “aftertempering” occurs, and the development of migration bloom can be delayed significantly. This heat treatment is application- and recipe-dependent and the total treatment is a multiple of time and temperature.
Bjarne Juul is senior technology specialist at AAK. He started there in 1991.
Form I II III IV V VI
Melting point °C 17.3 23.3 25.5 27.5 33.8 36.5
Systematic Nomenclature γ α β’2 β’1 β2 β1
Reprint from The Manufacturing Confectioner • May 2010
Beat Migration Bloom by Optimizing Your Process It appears that the process is the major part of many migration bloom problems and this opinion is supported by different investigations.
A typical well-tempered chocolate contains ap-
Tri-unsaturated tri-acylglycerols (TAGs) such as
proximately 2 to 4 percent Form V seed crys-
1-oleoyl-2-oleoyl3-oleoyl-glycerol (OOO) accel-
tals when leaving the tempering unit; the Form
erate the transformation from Form V to Form
V crystals just survive because of their higher
VI and it is very likely that the same will happen
melting point in this specific fat phase.
with the Form IV to Form V transformation.
An exception is a new technique that seeds
The tri-unsaturated TAG, OOO, is the major
with approximately 0.5 percent Form VI crys-
TAG in many nuts, e.g., hazelnut, almond and
tals, which ensures Form V crystallization in the
peanut, and all are frequently used in many
remaining 99.5 percent cocoa butter and is sta-
fillings in large amounts and migration bloom
ble enough to induce crystallization at a slightly
is often seen in this kind of application. In this
paper, the focus is on the tempering test, tem-
The purpose of all tempering techniques is
pering and the production cooling, especially
basically to start and ensure the Form V crys-
for shell cooling.
tallization in a chocolate. If a chocolate is not seeded correctly with sufficient Form V crystals,
the chocolate will crystallize in a lower form fol-
The traditional way of tempering is a process
lowed by transformation, resulting in problems
where all the chocolate is cooled to a tempera-
such as poor contraction and bloom.
ture where the fat phase starts crystallizing in a
Even producing a well-tempered (Form V)
mixture of Forms III, IV and V. This process is
chocolate does not guarantee that the rest of
based on the possibility of remelting all Form
the chocolate will crystallize in the same poly-
III and Form IV crystals in a following reheating
morphic form. The outcome is highly depend-
zone.Then, by testing the tempering curve on
ent on process cooling and heat treatments.
a standard instrument, it should be possible to
Too fast a cooling will favor Form IV crystalliza-
determine the tempering conditions of the final
tion even if the tempering has created perfect
Form V seeds. Too much heat treatment will
It is quite easy to evaluate the slope of a tem-
melt the seed.
pering curve but not as easy to evaluate the
The application has a significant influence
plateau level or inflection point of the curve.
upon bloom. For applications with only one fat
It is found that the plateau is correlated to
phase, such as solid bars or solid pralines, it is
the crystal stability and bloom stability of the
not very critical, whereas for applications with
chocolate.A lower crystallization plateau pro-
more than one fat phase, like filled bars and
duces less stable crystals and a less bloom-
pralines, it is much more critical and much
resistant chocolate. The target for the inflection
more difficult to understand.
plateau must therefore be as high as possible
Applications containing more than one fat
for a certain chocolate composition.
phase constitute perhaps 90 percent of all
It is well known that the fat phase composi-
bloom problems and for that reason it is the
tion affects the inflection point level. More milk
most important problem to solve.
fat in a recipe, for example, produces a lower
It appears that the process is the major part
inflection point. This fact does not directly influ-
of many migration bloom problems and this
ence the purity of Form V seed crystals because
opinion is supported by different investigations.
it is possible to adjust for it. But when tempering
2 May 2010 • Reprint from The Manufacturing Confectioner
Beat Migration Bloom by Optimizing Your Process equipment is unable to make the high inflection
evaluated. After the tempering test is finished,
level or there is ignorance about how important
the different chocolates are kept for 10 minutes
it is or how to change it, then it is much worse
at 15°C and refined on a grater and weighed
and more difficult to change.
into dsc (differential scanning calorimeter) cups and melted using the following program
COOLING FOR TEMPER TESTERS AND SHELL COOLING Nearly all tempermeters use a cooling tempera-
on a Mettler Toledo DSC 823: The temperature regime is 2 min. at 15°C and then 15°C to 60°C at +5°C/min.
ture somewhere between +7° and +10°C even
Figure 4 shows the correlation between the dsc
though cocoa butter prefers gentle cooling to
peak values for the melting curves and the cool-
ensure Form V crystallization. Years ago an ice-
ing temperature on the Exotherm equipment.
and-water bath was used; this was even further
It seems that the higher the cooling tempera-
away from “perfect” chocolate cooling.
ture, the higher the peak value, which indicates
Tests carried out in our pilot laboratory on a
a purer Form V crystallization.
Increasing the cooling temperature increases the inflection point of the chocolate. That indicates that more stable crystals are produced at higher cooling temperatures.
dark chocolate using a standard tempermeter have shown a clear correlation between the
Cooling and Temper Curve Slopes
chosen cooling temperature on the temperme-
The influence of cooling temperature on the slope of temper curves
ter and the inflection point level and slope for a certain chocolate (Figure 2). ing temperature in the tempermeter increases so does the slope. For example, the 17°C cooling temper ature gives a slope of +0.41, an indication of undertemper, that there is an insufficient quantity of
Temperature curve slope
From Figure 2 it can be seen that as the cool-
and slightly less heat in the heating zones of
0.4 0.3 0.2 0.1 0 7
Form V seed. To correct this, slightly lower cooling temperatures in the crystallization zones
Cooling temperature °C
the temperering unit are needed. Figure 3 shows the correlation between the inflection point for the same chocolate as used
Correlation of Inflection Point on Optimized Temper Unit 26.5
now the tempering unit has been optimized
(see above) for each of the four cooling temperatures on the tempermeter. It seems that increasing the cooling temperature increases the inflection point of the chocolate.That indicates that more stable crystals are
Inflection point °C
in Figure 2 and the cooling temperature, but
25.5 25 24.5 24 23.5
produced at higher cooling temperatures.
Cooling temperature °C
In Figure 4 the well-tempered chocolate from the above tempering-test measurements is
Reprint from The Manufacturing Confectioner • May 2010
Beat Migration Bloom by Optimizing Your Process Why do these special heat or cooling treatments sometimes improve bloom stability in filled products? In general, it is a question of compensating for some defects in the basic production.
Figure 2 shows that when making a temper
perature. Smaller amounts of Form IV crystals
test at a low cooling temperature the same
in mixtures with a lot of Form V will probably
chocolate would be undertempered if it had
make the chocolate unstable, too, but how
been measured at a higher cooling tempera-
much probably depends on the ratio between
ture, which actually is more similar to the tem-
the two polymorphs and the above-mentioned
perature used in production lines.
factors. Nobody knows how much Form IV
The lower the cooling temperature, the lower
“contamination” you can have in a chocolate
the inflection point, see Figure 3.The only ex-
without influencing contraction, gloss, etc.
planation for this kind of lower inflection point
Figure 5 shows a well-tempered dark choco-
for the same chocolate and lower values for
late cooled on a dsc with three different cooling
dsc peak (Figure 4) must be the different ratio
between Forms IV and V in the final chocolate
The chocolate is tempered on a 50 kg three-
samples. The more the cooling, the more Form
zone tempering unit and a small sample is
IV crystals are generated in the final chocolate.
weighed into preheated dsc cups and placed in
Pure Form IV crystals are very unstable and
the dsc equipment. The samples are stored for
for that reason they will quickly transform into
2 minutes at 28°C and then cooled with three
Form V depending on fat composition and tem-
different rates to 15°C, kept at 15°C for 10 minutes and then remelted at 5°C/min from 15°C
DSC Peak Values
to 60°C. The different values for the melting
33.5 33.4 33.3 33.2 33.1 33.0 32.9 32.8 32.7 32.6 32.5
Linear (Peak value)
peaks are shown in Figure 5. These results show the same tendency as
y = 0.0622x = 32.17 R² = 0.92
seen from the results mentioned in Figures 3 and 4. The faster the cooling, the lower the peak value and the wider the melting curves.
11 13 15 17 Cooling temperature °C
SPECIAL HEAT OR COOLING TREATMENT Individual companies sometimes use different
types of special treatment to optimize bloom
Cooling Rates vs. Melting Peak Values Cooling Rates 28°C –> 15°C Rate 0.3°C/min 10 min at 15°C 15°C –> 60°C with 5°C/min 28°C –> 15°C Rate 0.5°C/min 10 min at 15°C 15°C –> 60°C with 5°C/min 28°C –> 15°C Rate 1.5°C/min 10 min at 15°C 15°C –> 60°C with 5°C/min
Peak value °C melting curve 32.3
4 May 2010 • Reprint from The Manufacturing Confectioner
stability. Some store in cool conditions for a week or more, others store in hot conditions for a few days up to one week. Why do these special heat treatments or
special cooling treatments sometimes improve bloom stability in filled products? And why is this effect different from application to applica-
tion and time to time? In general, it is a question of compensating for some defects in the basic production. It seems that a heat treatment compensates for
Beat Migration Bloom by Optimizing Your Process a tempering with some amount of Form III/IV
The following example shows the effect of
formation and/or too fast a cooling of the choco-
heat treatment on milk chocolate with whole
late where some Form III/IV formation happens
afterwards. While alternatively a special “after”
A milk chocolate is well tempered and mixed
cooling compensates for too high a production
with 10 percent whole hazelnuts.
speed and for that reason an insufficient remov-
The mixture is deposited into 100 g moulds
al of crystallization heat from the product before
and cooled in a three-zone cooling tunnel (at
packing and an insufficient structure building
12°C, 10°C, 14°C) for 30 minutes, 10 minutes
in the filling. Often product is stored in rooms
in each zone.
held at 12°C to 16°C. During this special cool-
After cooling, all the tablets are stored for one
ing the TAG composition in fillings and shells
day at 20°C and then divided into four batches:
has found its optimum network structure.
• one batch is kept at 20°C for one week
Migration speed will be minimized and
• one batch is kept at 23°C for one week
therefore the migration-induced bloom will be
• one batch is kept at 25°C for one week
reduced. Again it is a compensation for insuf-
• one batch is kept at 28°C for one week
ficient cooling time in the production line and it
After one week all tablets are placed in a 20°C
actually takes much longer to remove all crys-
isothermal cabinet for bloom evaluation. Re-
tallization heat from a filling if it is in the center
sults from the bloom evaluation are found in
of a pallet and the risk of migration-induced
bloom is higher than if the product had been
Figures 7 and 8 show the difference between
cooled correctly at the start.
heat treatment and no heat treatment. The only
Bloom Evaluation Results
Weeks before visible migration bloom Special storage around nuts 1 week at 20°C, reference 29 1 week at 23°C 45 1 week at 25°C > 52 1 week at 28°C > 52 Figure 6
production difference between the two tablets is the one-week heat treatment. An analysis of the TAG composition of the chocolate at a distance of 0.5 mm from the nuts does not show a significant difference in the TAG composition. For both cases, migration of triunsaturated TAG (OOO) has taken place, but with two different bloom results.
Chocolate without Heat Treatment
Chocolate with Heat Treatment
One week at 20°C followed by 29 weeks at 20°C
One week at 28°C followed by 52 weeks at 20°C
It takes much longer to remove all crystallization heat from a filling if it is in the center of a pallet and the risk of migrationinduced bloom is higher than if the product had been cooled correctly at the start.
Reprint from The Manufacturing Confectioner • May 2010
Beat Migration Bloom by Optimizing Your Process Heat treatment at 28°C for one week purifies the polymorphism and at the same time inhibits visual bloom development for 12 months despite the oil migration.
Dsc performed on the chocolate at a distance
a real production line (Figure 9), which is one
of 0.5mm from the nuts shows a 0.6°C higher
example among many.
melting peak value in the chocolate which is
The application is a standard praline bar
heat treated at 28°C compared with the 20°C
with a soft “bloom-critical” filling inside and a
“heat-treated” chocolate, and exactly the same
dark chocolate shell.All the praline bars were
difference is found 10mm from a nut surface
produced one week before the test was start-
ed and all pralines were glossy and free from
It seems that heat treatment at 28°C for one
any bloom. The pralines were divided into two
week purifies the polymorphism and at the
batches and unwrapped.
same time inhibits visual bloom development
• Reference batch is kept for 24 h at 20°C be-
for 12 months despite the oil migration. This
fore it is stored in 15°C and 23°C isothermal
suggests that either the tempering or the cool-
bloom test cabinets
ing or both favored Form IV crystallization that
• Test batch is kept for 24 h at 25°C before it
was expressed as bloom in the non-heat-treat-
is stored in 15°C and 23°C isothermal bloom
It shows how important it is to control crystal
Other examples are tests made where some
development and ensure crystal stability to re-
FrozenCone (FCT) shells are heat treated be-
tard bloom development.
fore the filling is deposited.
A theory could be that if this transformation
Some dark praline shells are made on FCT
happens fully above the solidification point of
pilot equipment. Cooling is 3 seconds at 15°C
Form IV for this chocolate’s particular TAG com-
and the shell thickness is 1.5mm.Afterwards all
position, no visual bloom is developed and all
shells are cooled for 20 minutes at 12°C and
Form IV crystals are moved to Form V without
then divided into two batches.
bloom development. However, if this transfor-
Batch 1, reference
mation happens at a lower temperature, below
• Shells are filled with a nougat filling with high
the Form IV solidification temperature, larger
amounts of hazelnut paste
bloom crystals will appear.
• Cooled for 15 min at 12°C
One week at 28°C has speeded up the mi-
• Backed off and then cooled at 12°C for 30
gration to an equilibrium state and no essential
Form IV-to-V transformations happen after the
Batch 2, test samples
one week and therefore no bloom develops.
• Shells are stored for 30 min at 30°C
Of course, bloom will reappear when the
• Filled with nougat filling with high amounts of
Form V-to-VI transformation starts, but that
takes much longer and is therefore not the big-
• Cooled for 15 min at 12°C
gest problem for producers of filled products.
• Backed off and then cooled at 12°C for 30
The above theory explains the results from
Results from Heat-treated Filled Praline Bars 15°C isothermal cabinet 23°C isothermal cabinet Figure 9
6 May 2010 • Reprint from The Manufacturing Confectioner
Batch 1, Reference 20°C for 24 hrs 7 weeks, strong bloom 9 weeks, strong bloom
Batch 2, Test Samples 25°C for 24 hrs > 25 weeks, no bloom > 25 weeks, no bloom
Beat Migration Bloom by Optimizing Your Process The above two examples show how two dif-
microwaves early in the production process but
ferent heat treatments at different production
very difficult to control.
stages are able to compensate for some pro-
The optimal energy level and time is a ques-
tion of recipes, applications and fat composi-
The first examples (Figure 9) show that even
a one-week-old product is still able to be “repaired” by heat treatment, probably by a Form
V purification. It is the same phenomenon as
No two cases are the same with respect to mi-
seen in the earlier example (Figure 6) with ha-
gration bloom development.The application is
zelnuts in milk chocolate where migration hap-
too complex, therefore, it is important to look
pens but there is no visible bloom.
at all factors influencing migration bloom de-
The example in Figure 10 is slightly more
velopment before changing recipe, application
complicated with two variants in the trial—the
and process parameters, for example.
heat treatment and the storage time of the shell
The above examples show that the process is
a major factor as regards fast migration bloom
Dsc analyses show that the dsc melting peak
in chocolate products.
and end set of the shell increase around 0.3°C
A nonoptimal tempering process combined
when the shell is heat treated as mentioned for
with a too high cooling rate favor a final crystal-
batch 2, but only between a third to a half of
lization mix of Form IV and Form V and that
this increase in peak/end set value is caused
is probably the most common reason for fast
by the extra 30 minutes’ storage time. The re-
migration bloom.The transformation of some fat
mainder is due to the higher temperature (heat
from Form IV to Form V together with oil migra-
tion seems to have a larger influence on the de-
The conclusion is that this 30-minute pe-
velopment of migration bloom than expected.
riod at 30°C makes a significant difference to
Even though a chocolate shows a well-temper-
the shelf life, caused by some changes in the
ed curve, it does not guarantee the production
shell, maybe purification of Form V crystals in
of Form V seeds.The effect of heat treatments
the chocolate shells (which is supported by
shows that the chocolate is not perfectly tem-
the slightly higher dsc peak values) and/or a
pered and it is possible to purify the crystal pol-
type of aftertempering with longer residence
ymorphism even in a well-tempered chocolate
shell, adding more bloom stability as a result.
Tests have been done using microwaves as
It’s also important to realize that changing the
a fast online heat treatment method instead of
fat composition of a filling recipe will not solve
using longer times in heat cabinets. It is pos-
this process problem but only help to delay it.
sible to find the correct combination of energy
The objective is always to start with perfect
and time to delay bloom development by using
tempering at the highest inflection point level
A nonoptimal tempering process combined with a too high cooling rate favor a final crystallization mix of Form IV and Form V, probably the most common reason for fast migration bloom.
Results from Heat-treated FCT Shells—Filled Praline Shells 20°C isothermal cabinet 23°C isothermal cabinet
Batch 1, Reference 9 weeks, strong bloom 7 weeks, strong bloom
Batch 2, Test Samples > 25 weeks, no bloom 25 weeks, strong bloom
Reprint from The Manufacturing Confectioner • May 2010
Beat Migration Bloom by Optimizing Your Process A nonoptimal tempering process combined with a too high cooling rate favor a final crystallization mix of Form IV and Form V, probably the most common reason for fast migration bloom.
followed by a gentle shell cooling, which seems
polymorphism, followed by an extremely cold
to be a chocolate cooling rate of around -0.3°C/
filling-cooling zone, perhaps freezing zone, to
min, as shown in Figures 3 and 5.
ensure a high degree of network structure and
This very low cooling rate is of course expect-
small crystals, and finally a short reheating
ed to be more important at the start of cool-
zone to remove any possible condensate on the
ing rather than later on and it will depend very
much on air velocity, crystallization heat from
Before doing that we have to carry out more
center, shell thickness, size of application, etc.
studies to test a lot of different applications, fat
After that it is more a question of application,
compositions and other variables to find the
the fat composition of the filling and optimal
correct cooling condition for a certain applica-
storage.The less”optimized” a chocolate is in
its crystallization progress, the more sensitive it is to incorrect process parameters.
This paper indicates that a cooling rate in a
- AAK pilot laboratory, Aarhus, Denmark
well-tempered chocolate shell should be at a
- Beckett, Steve. Industrial Chocolate Manu-
maximum of -0.5°C/min to ensure a sufficiently
facture and Use, Second Edition, pp 186,
pure Form V crystallization with a high degree
of bloom stability.
- Minifie, Bernard W. Chocolate, Cocoa and
At the same time, it is important to make sure
Confectionery: Science and Technology.
that the tempering process is producing very
Third Edition. Page 212.
pure Form V seeds to ensure a very high inflec-
- Smith, Kevin, Geoff Talbot. Food Chemistry.
tion point measured at a production-realistic
- Timms, Ralph E., PhD. The Manufacturing
Confectioner, June 2002.
A perfect cooling tunnel for the future could
- Ziegleder, G, Dr. Dr.–Ing habil. Frauenhofer
be a tunnel which starts with a traditional gentle
Institut, ZDS Fat Bloom Symposium, May
shell-cooling zone, followed by a short heating
16 –17, 2000.
zone (perhaps micro waves), which purifies the
8 May 2010 • Reprint from The Manufacturing Confectioner
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