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Hard Candy Variations
Effects of Corn Syrup
Lab 1
OVERVIEW
Hard candy is made of a mixture of sucrose and corn syrup, cooked to high temperature to remove
moisture, and cooled rapidly to form a sugar glass. The properties of the sugar mixture depend on the
type and level of corn syrup added. In this lab, we will prepare different mixtures of sugar and corn
syrup to evaluate the effects of formulation (reducing sugars) and process conditions (cook temperature)
on color development and moisture uptake.
OBJECTIVES
(1) To illustrate the effects of different types of corn syrups on color and water uptake in hard
candies.
(2) To illustrate the effects of different ratios of sucrose to corn syrup on color and water uptake in
hard candies.
(3) To illustrate the effects of cook temperature on color and water uptake in hard candies.
BACKGROUND
Corn syrups are added to sucrose in manufacture of hard candies primarily to prevent graining
(controlling sucrose nucleation and growth). The type and amount of corn syrup used can affect
sweetness, texture, color development and moisture uptake (hygroscopicity) of the final product. By
balancing these effects, the candy maker can produce a high quality product with the desired
characteristics.
Commercial corn syrups have different properties depending on the manufacturing process. The
most important properties include the DE (dextrose equivalent) value, specific saccharide composition
and viscosity. Each of these is related to the other since it is the molecular composition that determines
both DE and viscosity. One of the most important characteristics of corn syrup is the DE (Dextrose
Equivalent). DE is a measure of reducing power of a product calculated as glucose and expressed as
percent of total dry substance. The DE value gives an average of all the reducing sugar ends of the
molecules in the corn syrup but does not give an indication of the range of saccharide composition. The
concentrations of the different saccharides (monosaccharides through oligosaccharides) may be very
important for a specific application since each molecule has different behavior in the sugar matrix. For
example, the short chain molecules (primarily glucose) are responsible for the hygroscopicity of corn
syrup. Viscosity of corn syrup is another important characteristic, dependent on molecular composition.
Long-chain molecules enhance viscosity more than short-chain molecules, so typically a high conversion
corn syrup (e.g., 62 DE) is significantly less viscous than a low conversion (e.g., 36 DE) corn syrup. In
general, viscosity of corn syrup decreases as DE increases. The saccharide profile is always about the
same for a given DE as long as the conversion process is defined (i.e. acid converted, acid-enzyme
converted, enzyme-enzyme converted).
The DE of a corn syrup can be calculated from its component parts. The weight percent composition
of each component saccharide is multiplied times the specific DE of that component and the DE
contributions of each component are summed to give the final DE of the corn syrup. An example of a DE
calculation is shown in Table 1. For mixtures of sucrose (nonreducing) and corn syrup, the total reducing
sugars (%) can be calculated simply as the product of the weight fraction of corn syrup and its DE. For
example, a mixture of 50/50 (% dry basis) sucrose and 42 DE corn syrup would give a total reducing
sugar content of (0.50 times 42 = 21%). Note that corn syrup as used in the industry is about 80% solids
and 20% water (43 Baume’) so if the sucrose to corn syrup ratio is given on a wet basis, as is often done in
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industry, then the dry solids percentages must be calculated before the percentage of reducing sugars can
be found.
Total reducing sugars in a hard candy affects color, equilibrium relative humidity (ERH), sweetness
and shelf life. Reducing sugar content depends on the type of corn syrup used and the level of corn
syrup in the formulation. However, inversion of sucrose into glucose and fructose during cooking
(temperature, time and pH dependent) can cause a significant increase in reducing sugar content in a
hard candy. That is, inversion occurs more rapidly at higher temperatures and low pH, so the longer an
acidified candy is held at high temperature, the less sucrose (and more glucose and fructose) will be
present in the final candy.
Definitions
Corn starch
Corn syrup
Baume'
DE
ERH
Hygroscopicity
polymeric molecules of glucose found in corn
a sweetener made by hydrolysis of corn starch (sometimes called glucose syrup)
scale for hydrometer readings (measures specific gravity or density)
Dextrose Equivalent: measure of reducing power
Equilibrium Relative Humidity: the RH of air at which a product neither picks
up or loses moisture
Capacity of a material to pick up moisture from surrounding air
APPARATUS
Copper cooking kettles or electric skillets
Gas burner
Stirring spoon
8 oz. glass jars
Aluminum pans for weighing
Balance
PROCEDURES
The 27 formulations shown on the attached Table 2 have been pre-weighed for you in the copper
kettles (or electric skillets). In addition to the sweeteners, approximately one part of water per two parts of dry
sugar is added in order to dissolve the sugar. All batches have the same total weight so that cooking times
should be constant, but record the time from when your batch starts to boil to when it reaches the
desired temperature.
Stir the formula slowly as it heats. When the sugar is completely dissolved, it is no longer necessary
to stir. Keep the flame (or electric setting) rather low when temperature is between 230 and 250°F
because there will be moderate foaming. After foaming has subsided, the gas fire (or electric setting) can
be increased slightly. However, we want to keep the cooking rate as constant as possible for all cooks so
that the cooking times are constant and are not a factor in color comparisons.
Shut the flame off at the required final temperature and quickly fill the two metal weigh boats about
half full by using the wooden spoon. Be careful to control the amount of syrup in each weigh boat. Then
carry the kettle to the cooling table and pour it out. With a knife, score several one-inch squares that will
be used for moisture uptake tests. When the candy is cool, break off enough squares to fill an 8 oz. jar
identified with your code number. Note that the syrup is still losing water while it is held at high
temperature even though the flame is not on and the syrup is not boiling. So be as quick as possible
(while still being safe) once your syrup has reached the desired temperature.
Cautionary note. Sugar syrup at 300°F is extremely hot and therefore, extremely dangerous. If you
get any of it on you, it will burn you severely before you get a chance to wash it off. Always use gloves
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when handling hot surfaces, never touch a hot sugar syrup with your hands and be careful not to allow
the syrup to spill when you carry the kettle to the table. Be very, very careful!
Record the weight of one of the aluminum weigh boats (use an empty weigh boat to tare the scale).
Place these samples in the oven at elevated temperature and humidity. Tomorrow morning weigh your
sample again (remember to tare the scale again with an empty pan). Calculate the percent moisture
pickup (see below) and report the results in the appropriate column in Table 2. Please let me know if you
can not weigh your sample during this time period and we’ll make other arrangements for you.
Percent moisture pickup can be calculated as follows:
% moisture pickup = {(Wf - Wi)/ Wi}x 100
where Wf is the final weight and Wi is initial weight of sample.
The second weigh boat will be used to measure color with the Hunter colorimeter. Each sample will
be placed on the stand and the L,a, b values recorded at three points on the disk. The average of the three
readings should be recorded in Table 2. These samples will also be used to measure water content (Karl
Fisher titration) and Tg (differential scanning calorimeter).
You need to calculate the percentage of reducing sugars in each formulation. The remainder of Table
2 will be filled out in the follow-up class period based on data obtained from each of the other students.
DATA ANALYSIS AND DISCUSSION OF RESULTS
Once all the data has been compiled, you need to analyze the results. This data set provides
numerous comparisons and correlations that demonstrate the principles discussed in class. Some
example of analyses/correlations for you to consider include:
1. What factors affect Tg?
2. What factors affect water content?
3. What factors affect color development?
4. What factors affect water sorption?
5. What other connections can you make?
ADDITIONAL QUESTIONS
1.
What would be effect of using more or less water in the sugar mixture before boiling?
2. If you were to use high fructose corn syrup (basically a 97 DE corn syrup in which some of the
glucose is enzymatically converted to fructose) to make a hard candy, what would you predict would
happen to color and moisture uptake and why.
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3. Was your hard candy sticky after the moisture sorption test? What factors do you think affect
stickiness of hard candies? Which ones would you predict would be most sticky and which would be
least sticky? Why?
Table 1. Determination of dextrose equivalent (DE) from corn syrup composition. Example provided for
acid-converted 42 DE corn syrup as provided by ADM (see corn syrup specification sheets).
Composition1
(weight %)
Observed2
DE
Contribution3
To DE
Monosaccharides
20
100.0
20.0
Disaccharides
14
58.0
8.12
Trisaccharides
12
39.5
4.74
Tetrasaccharides
9
29.8
2.68
Pentasaccharides
8
24.2
1.94
Hexasaccharides
7
20.8
1.46
Hepta and higher
30
10.2
3.06
Total
100
Component
42.04
Composition given in specification sheet
DE of pure individual component, based on experimental measurement (courtesy of ADM)
3 Product of composition (in weight fraction) times observed DE of component
4 Sum total of all contributions to DE
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Code
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25
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27
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Composition
Sucrose/Corn
Syrup (%dry
basis)
70/30 36 DE
70/30 36 DE
70/30 36 DE
70/30 42 DE
70/30 42 DE
70/30 42 DE
70/30 62 DE
70/30 62 DE
70/30 62 DE
70/30 36 DE
70/30 36 DE
70/30 42 DE
70/30 42 DE
70/30 62 DE
70/30 62 DE
70/30 36 DE*
70/30 36 DE*
70/30 62 DE*
70/30 62 DE*
50/50 42 DE
50/50 42 DE
50/50 42 DE
30/70 42 DE
30/70 42 DE
30/70 42 DE
100 Sucrose
100 Total Invert
100 Maltitol
Syrup
Cook
Temperature
(°F)
Cook Time
(min.)
Reducing
Sugars (% dry
basis)
305
305
305
305
305
305
305
305
305
285
285
285
285
285
285
285
285
285
285
305
305
305
305
305
305
305
289
305
Final H2O
(measured %)
10.8
10.8
10.8
12.6
12.6
12.6
18.6
18.6
18.6
10.8
10.8
12.6
12.6
18.6
18.6
10.8
10.8
18.6
18.6
21.0
21.0
21.0
29.4
29.4
29.4
0
100
0
Table 2. Hard candy compositions and data sheet.
* Milk solids added to promote mailard browning
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Color
Moisture Pickup (g/100 g
candy)
Texture
comments
RESULTS AND DISCUSSION
The intent of this lab was to provide an introduction to the most important aspects of sugar
confectionery – the properties of sugar syrups. The 27 formulations were designed to provide quite a
range of different compositions and process conditions to give differences in color development,
moisture content, moisture uptake and glass transition temperature (Tg). Several replicate conditions
were included to note the variability from batch to batch.
From the data collected from the entire class (Table 2 above), numerous connections and
interactions that demonstrate the physico-chemical principles of cooking sugar syrups can be made. A
good lab report would fully develop these connections along with an explanation of the scientific
principles involved. Places where the data deviate from expected trends should be noted and reasons for
these deviations suggested.
Variability between duplicates:
Comparing first the cook time, not surprisingly there were probably some differences between
the replicate samples. Cook time was a function of the gas flame height and since that was not controlled
between groups, it’s not a surprise if the time to reach cook temperature varied between duplicates.
These differences in cook times will have caused differences in the amount of sugar hydrolyzed
(inverted) during cooking. Thus, differences in cook time lead to differences in color development. If
cook temperature and cooling time (time from reaching cook temperature to solidification on the table)
were exactly the same in replicate samples, we would expect moisture content to be the same. However,
moisture changes continue to occur as long as the syrup is held at elevated temperatures and since each
person was more or less quick about pouring samples and solidifying the mass, we observe differences in
moisture content. These differences in moisture content lead to differences in Tg and moisture sorption.
Thus, even though these samples were duplicate formulations, the differences in process conditions led
to differences in physical properties. This is an important point to recognize – the end result in your
candy will often be due to slight deviations in process conditions.
Initial moisture content:
In general, the moisture content of the candies after solidification should be related to the boiling
point elevation for that composition. At the designated cook temperature, the amount of water
remaining is governed by this boiling point elevation. Since boiling point is determined by the number
and molecular weight of the sweeteners, those formulations with more and smaller molecules should
have a higher boiling point for a given weight of sweetener added. Thus, we would expect that higher
DE formulations (more smaller molecules) would have more water remaining, for a given cook
temperature, than lower DE formulations (more larger molecules). Also, we would expect that a lower
cook temperature would leave more water remaining, so the formulations cooked to lower temperature
should have higher moisture content.
Another trend we would expect to see is that identical formulations cooked to different
temperatures would have different initial water content.
Furthermore, the formulation with all invert sugar should have the highest water content. This
formulation had the highest level of low molecular weight sugars and was cooked only to low
temperature, both factors that led to the high water content.
Color development:
Color in cooked sugar syrups comes from a combination of Maillard browning, the reaction
between reducing sugars and amine (protein) compounds, and caramelization. Important factors that
affect color development include the amount of reducing sugars present, the presence of amine
compounds, the cook time and temperature. In general, formulations with high levels of reducing sugars
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that are cooked for a long time at elevated temperatures would be expected to have the brownest color.
Note that corn syrup has very little protein, but does have small amounts of amine compounds, which
are sufficient to promote Maillard browning. In these experiments, the brown color is indicated by the L
value obtained from the Hunter colorimeter, with lower L values indicating more brown color.
For a given cook temperature, we would expect the L value to decrease as the amount of
reducing sugars increased and cook time increased. When there is variability in replicates it is probably
due to the differences in cook time. Formulations cooked to lower temperature would be expected to
have less color.
Glass transition temperature:
The temperature at which the liquid syrup turns into a solid glassy matrix is the glass transition
temperature (Tg), in this case measured by calorimetry. The two main factors that affect Tg are molecular
weight of the sugars in the syrup and the final water content. In general, the more smaller molecular
weight materials and the higher the water content, the lower Tg. In this experimental data set, both
average molecular weight and water content varied with the formulations and cook process.
One indicator of average molecular weight is the amount of reducing sugars present. In general,
the higher the reducing sugar, the more smaller molecules are present and the lower the average
molecular weight. Thus, we would expect a decrease in Tg with an increase in reducing sugars (lower
average molecular weight).
The second factor that affects Tg is water content. There is a decrease in Tg with increasing water
content.
Moisture sorption:
The hygroscopicity, or propensity to pick up moisture from the environment, of a sugar glass
depends primarily on the composition. It is well known that smaller molecules (like glucose and
fructose) are more hygroscopic than larger molecules, even sucrose and especially the larger glucose
polymers. Thus, we might expect a relationship between moisture sorption and reducing sugar content
of our formulations. Moisture sorption may also be a function of water content since the ability of a glass
to pick up moisture depends on how easily the molecules move around and make room for the water to
penetrate the glassy matrix.
Since Tg depends on both chemical composition and water content in much the same way as
moisture sorption, it is interesting to explore the relationship between sorption and Tg. In a general
sense, formulations that lead to lower Tg, either through addition of lower molecular weight components
or by adding water, result in more rapid moisture sorption.
Other results:
Some of the formulations were made in electric skillets instead of being heated in the copper
kettles over open flame. Does the source of heat have any effect on the results?
One formulation was made with all sucrose. Without the addition of corn syrup or invert sugar,
there was nothing to inhibit the crystallization of sucrose and this formulation was seen to grain by the
time it was poured onto the table. Another formulation was made with all invert sugar, a system that
will not crystallize but will also not form a glass at room temperature. This system was still an
amorphous fluid upon cooling on the table.
Improvement of experiment:
The primary uncontrolled variable in this experiment was the cook time. Some method of
controlling heating to minimize variations in cooking times would be beneficial for reducing the
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variability in physical properties. Perhaps cooking all formulations in electric skillets with
predetermined settings would minimize such differences.
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Corn Syrup & Sugars in Hard Candy
Hard Candy Lab 1
Discussion
Allan Buck
Archer Daniels Midland Co.
Resident
Course in
Confectionery
Technology
Effects to be Observed
• Effect of DE of Corn Syrup
– Color, hygroscopicity, texture, flavor
• Effect of cook temperature
– Color, hygroscopicity, water content
• Effect of reducing sugars in formula
– Color, hygroscopicity, texture,
sweetness
Resident Course in Confectionery Technology
Experimental Design
Ingredients Percent
(dry basis)
Reducing
Cook
Temperature Sugars
Theoretical
Moisture
Sucrose
26 DE
65%
35%
305º F
10.0%
3.4%
Sucrose
42 DE
65%
35%
305º F
14.7%
3.4%
Sucrose
62 DE
65%
35%
305º F
21.7%
3.4%
0.1% Monosodium Glutamate added to each formula
Resident Course in Confectionery Technology
Effect of DE on Hard Candy
Color
26 DE
42 DE
62 DE
0.1%
0.1%MSG
MSGadded
addedto
toenhance
enhancecolor
colorresponse
response
Resident Course in Confectionery Technology
Effect of Protein on Browning
Sugar, corn syrup and evaporated milk
25 min
(225°F)
40 min
(246°F)
50 min
(248°F)
Resident Course in Confectionery Technology
Sugar and corn syrup only
60 min
(250°F)
Caramelization
O
H
OH
OH
HO
O
OH
H
HO
H
H
OH
HC
H 2O
H
H
OH
H
OH
H
OH
H
OH
H
OH
H
OH
OH
D - g lu c o s e
OH
lo w p H
H
CH
3
H
H
CH
CHO
O
2 - fu r fu ra l
H 3C
CH
O
CH
O
3
HO
O
a c e to l
p y ru v a ld e h y d e
O
OH
HO
CHO
O
H 3C
3
d ia c e ty l
H
HMF
O
O
3
OH
3 -d e o x y -D - g lu c o s e
OH
HO
OH
g ly c e r a ld e h y d e
HO
d ih y d ro x y a c e to n e
O
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OH
Maillard Browning
O
RNH
HOHC
H
O H
HO
H
H
O H
H
O H
H
O
H
3C
HO
O H
NH
O H
2
a m in o a c id o r p ro te in
H
H
O H
H
O H
O H
O H
D -g lu c o s e
D -g lu c o s y la m in e
R
R
NH
NH
O
HO
R
N
O H
H
HO
H
H
H
O H
H
O H
H
O H
H
O H
O H
HO
O H
H
H
O H
H
O H
O H
O H
A m a d o ri R e a rra n g e m e n t
O
2 -fu rfu ra l
O
O
HOC
H
H
2N
CH
lo w p H
H
H
H
O H
H
O H
+
5 HM F
3
p y ru v a ld e h y d e
O H
3 -d e o x y -D -g lu c o s o n e
d ia c e ty l
a c e to l
B r o w n in g P ig m e n ts
Resident Course in Confectionery Technology
H
2O
Functional Use and Degree of Conversion
Function
Low DE
High DE
Body Agent
Prevent Crystallization
Viscosity
Foam Stabilization
Browning Reaction
Sweetness
Hygroscopicity
Humectancy
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Relative Sweetness of Nutritive
Sweeteners*
36 DE CSU
42 DE CSU
62 DE CSU
42% HFCS
55% HFCS
Lactose
Dextrose
Fructose
Sucrose
35-40
45-50
60-70
100
100-110
40
70-80
150-170
100
*Handbook of
Sugars, 1980
Resident Course in Confectionery Technology
Properties of Hard Candy as a
Function of Sugar/Corn Syrup Ratio
100% Sucrose
Super
saturated
Very sweet
100% Corn
Syrup
Highly
concentrated
Low sweetness
High flavor
release
Low
machinability
Low flavor
release
High
machinability
Resident Course in Confectionery Technology