Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Effects of the Baking Temperature and Time on the
Quality of Biscuits
Anis Alam Siddiqui1 and Lubna Nasreen2
Abstract: Baking is obviously one of the most important stages of
biscuits production. Baking time and oven temperature have greatest
effects on biscuit quality. Several studies have shown that the physical
properties of dough and the recipe of biscuit making depend on the type
of biscuit and the methods used in dough formation. The aim of this
study was to investigate the effect of baking time- temperature and
humidity on biscuits quality. The study also investigated the quality of
flour used for biscuit manufacture and studied the ultimate quality and
shelf life of some brands of biscuits in Nabisco Biscuit & Bread Factory
Ltd, Dhaka, Bangladesh. The study showed that the baking temperature
and time were 240 °C for 5.5 minutes, and 250 °C for 3-4 minutes
respectively for 5 mm diameter biscuit in average. The biscuits baked at
lower temperature and longer time had the lowest moisture. Higher
temperature takes less baking time on the other hand lower temperature
takes longer baking time. The increase or decrease of time- temperature
combination is adjusted with speed of the conveyor belt. The study also
explained the mode of heat transfer in the oven during baking process.
Keywords: baking, flour, biscuit quality, time- temperature, heat
transfer, dough formation, moisture, speed of conveyor belt etc.
Introduction
Biscuits, which are chemically leavened baked products, are one of
the most delicious foods liked by most people. They are stable
foods and have advantages such as long shelf life and good eating
quality. The physical properties of the dough and the recipes in
biscuit making depend on the types of biscuit and the method used
in the dough formation. Quality standards from the raw materials
1
Associate Professor, Department of Food Engineering & Technology, State
University of Bangladesh
2
Lecturer, Department of Food Engineering & Technology, State University of
Bangladesh
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
to the end product are essential in biscuit making to ensure food
safety.
The delicious smell of biscuit is produced as a result of the
interaction of various chemical and physical processes that can be
adjusted to create a great variety of products. Baking is obviously
one of the most important stages of biscuits production. Biscuit
quality and baking time also change with oven design and
operating parameters. These parameters must be well established
and controlled for each type of baked products. In the production
of biscuit dough, dough-mixing procedure, packaging of the
product, storage period should be well established for high quality
product. Baking time and oven temperature have greatest effects
on biscuits quality.
The aim of this study was to investigate the effects of baking time
and temperature on biscuits quality and its shelf life to investigate
the effects of baking temperature, time and humidity on biscuits
qualities and subsequently find the relationship between biscuit
crust and crumb properties. This study has evaluated the effects of
different temperature and time combination on the quality of
biscuits.
Baking is a very important process but is very complex and
somewhat difficult to understand and describe. The design and
control of an oven is principally a matter of heat transfer, but for
the baker it is a matter of temperatures and turbulence at specific
stages.
Heat and temperature are not the same and should not be confused.
It is relatively easy to measure temperatures in an oven but much
more difficult to measure heat, or heat flux, which is the rate at
which heat is being transferred. Heat is transferred much more
effectively if the air is moving near the dough piece at a given
temperature.
Nearly all biscuits are now baked in band or travelling ovens with
several independently controlled zones. This means that oven
conditions such as temperature, movement and humidity of the
atmosphere may be altered during the course of the baking period.
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Baking times for biscuits are quite short, ranging from 3-5
minutes. It is not normally possible to change quickly, the
temperature of a static or reel oven so the results of baking in these
ovens compared with that in travelling ovens are often very
different.
The conditions needed for different types of biscuit are not the
same because the way in which the structure is developed and the
amount of moisture that must be removed depends on the richness
level of fat and sugar of the recipe.
Materials and Methods
Materials: The principal raw materials for biscuit manufacture
were flour, milk powder, sugar, sodium bicarbonate, mould,
potable water, flavor, etc.
Equipments: Direct Gas Fired (DGF) oven was used with
visibility of the burners. Control options extend from a PLC with a
touch screen operator interface to a full SCADA system. Variable
speed fans instead of dampers provide a linear response for
improved process control. PMB moisture analyzer, with heating
element: Single 400 wart halogen heater and operating temperature
was 30-104ᵒF \ 0-40ᵒC was used for analysis of moisture.
Refractometer and digital pH meter were used for determination of
brix and pH respectively.
Place of Experiment: This experiment was conducted by the
department of Food Engineering & Technology, State University
of Bangladesh, at the Quality Control Laboratory, Nabisco Biscuit
and Bread Factory Ltd. Dhaka, Bangladesh.
Analysis of Flour: In this study commercially available flour of
different brands such as Dawan from Dawan Flour Mills,
Narayngong; Green Bird from Mofiz Flour Mills, Tangail; Islamia
from Islamia Flour Mills; Sonali from Sonali Flour Mills, Tangail
and ACI pure from ACI pure Flour Mills, Narayngong were used
as principle raw material depending on the types of biscuit. At first
the moisture content of flour was tested. Five (5) gm of each flour
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
sample was tested for moisture content using PMB moisture
analyzer, which had heating element: Single 400 wart halogen
heater and operating temperature was 30-104ᵒF \ 0-40ᵒC.
Gluten content of flour was tested by analytical method. 50 gm
flour was taken to prepare dough using 25 ml 2 % NaCl solution
and mixed into dough with a spatula. Then was kneaded the dough
gently under water for 10-15 minutes, so that soluble matter and
starch were washed away. KI was used to control presence of
starch. Then rolled dough into a ball was weighed the moist gluten
and expressed as percentage of flour. Then it was dried at 100oC
to constant weigh and expressed repeat as a percentage of flour.
Test of milk powder: Fresh milk powder (Manufacturing date:
20-07-2011 and Expire date: 20-01-2012) was tested for solubility
properties, color and flavor.
Brix analysis of sugar: 50% sugar solution was prepared and
tested by refractometer. The brix chart (adjusted with temperature
of that day using thermometer) was used to obtain brix of sugar
solution.
pH test of potable water: Digital pH Meter was used to test pH of
water.
Preparation of biscuits: Formulation of biscuits is shown in
Figure-1. The volatile flavor of interest was added at the creaming
stage, using propylene glycol (1 ml) as the carrier solvent, ultimate
concentration 250 ppm by weight. Volatile loss during the mixing
step was not quantized, but would not have been considerable at
room temperature. However, mixing was minimized to avoid this
loss, without compromising thorough distribution of the volatiles.
Extraction and analysis of volatiles from individual finished
biscuits showed a low level of biscuit-to-biscuit variation,
suggesting that the mixing stage was efficient (Michael S. Brauss
et al., 1999). In order to examine the effect of baking time on
volatile release in-nose, dough samples from the same batch were
baked in the cookie oven for various times.
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Figure 1: Flowchart illustrating production process for biscuit
manufacture
Moisture test of biscuits: PMB moisture analyzer, having heating
element: Single 400 wart halogen heater and operating temperature
was 30-104ᵒF \ 0-40ᵒC was used to test moisture content of Sugar
free biscuit, Carlton biscuit and Glucose MPP biscuits after
production. Five (5) gm of powdered biscuit was used to perform
this operation.
Organoleptic tests of biscuits: The organoleptic properties of
Butter Cookie, Glucose MPP, All Time, Sugar free biscuit and
Carlton biscuits were tested. Color, flavor, texture, bite, acoustics
(cracking of biscuits), baking color, foreign material, objectionable
material, metallic contamination, sour taste and burnt properties
were frequently tested.
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Shelf life study of biscuits: Biscuit weight and moisture were
measured weekly to test shelf life.
Results and Discussion
Effect of time-temperature combination: The oven has 6 zones
for controlling temperature. The different zones with gradual
increase or decrease of temperature are named as:
a) Heating zone (zone-1 & 2)
b) Baking zone (zone- 3, 4 & 5)
c) Coloring zone (zone-6)
The average temperature of zone-1 and zone-2 was relatively
warmer- 95.65°C and 177.39°C respectively (Table-1). The
warmer the temperature, the more active our yeast will be. The
more active our yeast is, the quicker the dough rises. In these zones
relatively all moisture of dough are removed. The loss of moisture
from biscuit is related to the temperature, heat flux and water
vapor at the surface. Moisture is lost from the dough surface
because of migration of water to the surface by capillary action and
diffusion. Both of these phenomena are accelerated by temperature
gradients. The centre of dough piece is heated principally by
conduction of heat, but as the crust dries it act as an insulator and
make it more difficult to heat the centre. (Chevallier et al., 2002).
During this period color change occur prematurely. The average
temperature of zone-3 is 214.34°C. In this zone gas bubbles and
water vapor are formed which expand and result in a large
reduction in the density of the dough. The possible reason of this
mechanism includes heating of starch and gluten resulting in
gelatinization of starch and denaturation of gluten; which cause
swelling (Chevallier et al., 2000). Bubbles of gas are liberated due
to increasing temperature which also increases the water vapor
(Broyart et al., 2002). The average temperature for zone-4 and
zone-5 was 302.60°C and 324.34°C respectively. During this
period, the characteristic color and flavor of biscuit is developed.
The color becomes yellowish brown, which merely darkens
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
(Mundt et al, 2007). Reduction in reflectance of the biscuit surface
also occurs (Shogren et al., 1998). The possible mechanism is
occurrence of maillard reaction and non-enzymatic browning,
which involves the chemical reaction between reducing sugars in
the dough with proteins and produces the attractive color (Brauss
et al, 1999). Color also develops from caramellization of sugar. In
order to prevent parts of the edges of the dough pieces becoming
over colored it is important to arrange that they are placed close
together on the oven band with adjusted spaces between them. If
edges are over heated or burnt, then biscuit is not packaged or
rejected. The average temperature of zone-6 is 169.56°C. During
this period desired texture of biscuits is obtained (Ahmad et al.,
2001).
Table 1: Temperature Monitoring by Oven Thermometer
Oven zones
Parameters
Levels
Zone1
Zone2
Zone3
Zone4
Zone5
Zone6
Temperature
(ᵒC)
Mean
95.65
177.39
214.34
302.60
324.34
169.56
Table 2: Time-Temperature combination
Baking time
Zone 1
Zone 2
Zone 3
Zone 4
3.0 – 4.0 min.
210°C
290°C
320°C
180°C
5.5 min.
180°C
270°C
310°C
200°C
Oven temperature is always controlled. Speed of the conveyor belt
is adjusted according to temperature of the oven. At the above
adjusted temperatures of different zones of the oven, 5 mm
diameter thick biscuit takes about 5.5 minutes to be completed.
Table-2 shows that if baking time is lowered to 3-4 minutes from
5.5 minutes, subsequently baking temperature is increased.
Temperature of zone 1 increased from 180°C to 210°C. Same
phenomenon occurs in case of other zones (Table-2). If the speed
of conveyor belt is made slower or faster, then temperature of the
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
oven must be adjusted depending on the speed. Otherwise biscuit
will not be produced properly.
Thus baking is a matter of finding the best conditions of heat and
time to allow structure development, surface coloration and drying
of centre. Thicker biscuits need longer bake times at lower
temperatures to achieve this drying. Thin and small biscuits can be
baked faster at higher temperatures.
Heat transfer process during baking: Direct Gas Fired (DGF)
oven was used with visibility of the burners. The heat is provided
by burning gas and transferred by the three modes known as
radiation, conduction and convection. Three modes are always
involved though engineering techniques are used to enhance the
effects of each separately. Dough pieces are supported on a baking
surface which is usually a sheet of steel. On entering the oven, heat
is applied to the dough piece by a combination of conduction
(through the baking surface), convection (from the hot air moving
in the oven) and radiation (from hot surfaces of the structure of the
oven). Radiant heat, at the wave lengths involved, does not
penetrate the dough piece significantly. The most effective form of
heat transfer is by convection but moving hot air also sweeps away
moisture and dries the dough surface very rapidly.
Moisture removal process: As the moisture evaporates from the
product a rise in pressure in the oven occurs. In the case of direct
fired ovens where gas is burnt in the baking chambers, the increase
in pressure is even greater. This pressure must be relieved so flues
are provided which exhaust to the atmosphere.
Later, as the dough temperature rises, water will again evaporate
and retard the rate at which the surface temperature rises. The
wetting of the dough surface at the oven entrance aids the general
rise in temperature of the dough piece and maintains the flexibility
of the "crust" longer. It would be ideal if the dough piece could be
heated uniformly and rapidly before much moisture is lost. During
this drying phase and before the surface becomes too dry the
temperature may be adjusted to give a desired level of coloration to
the biscuit.
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Quality of the raw materials: Moisture is an important parameter
in flour that significantly affects shelf life and growth of microbial
contaminants (ICMSF 1998). In the BDS 382 as well as in the
Codex Alimentarius Standard (1995), the maximum moisture in
flour is defined as 13% and 15.5%, respectively (Siddique &
Chowdhury, 2013). In this study the moisture in Bangladeshi
wheat flour samples used in biscuit manufacture were tested,
which ranged from 12.15 ± 0.26% to 13.63 ± 0.59%. Gluten
content of different flour brands ranges from about 22-26 g in
100gm. Wheat flour of these gluten ranges are appropriate for
biscuit manufacture. Only ACI brand had 38 g of gluten. That’s
why this flour is used for bread making instead of biscuit.
Milk powder had proper solubility property and desirable color and
flavor. Brix of sugar was satisfactory and pH of water used in the
operation was 7.2.
Table 3: Chemical quality parameters of wheat flour samples
Parameters
and
legal limits
Levels
Moisture (%)
Max 13%2
Max15.5%3
Gluten (within
100 g)
Brand Name 1
G
S
D
A
I
Mean ±
SD
12.52
± 0.70
13.12
± 0.42
12.92
± 0.37
12.77
± 0.49
12.63
± 0.76
Mean ±
SD
24.30
± 0.05
22.37
± 0.07
27.8
38.87
±
0.049
28.28
±
0.062
± 0.09
1: Brand name: G-Green Bird, S-Sonali, D-Dawan, A-ACI Pure, I-Islamia.
2: Maximum acceptable limits of wheat flour according to BDS 382:2001
3: Maximum acceptable limits of wheat flour according to Codex Alimentarius
Standard (1995).
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Siddique, AA & Nasreen, L
Journal of SUB 5(1): 1-12, 2014
Table-4: Quality test of different brands of biscuits
Name of
Biscuit
Butter
Cookies
Glucose
MPP
All Time
Sugar
free
biscuit
Carlton
biscuit
Interval
between Mfg. &
testing (day)
0
14
16
45
0
Moisture
(Max-5)
1.77
1.79
2.08
2.13
1.39
14
1.39
16
45
0
14
16
45
0
14
16
45
0
14
16
45
1.45
1.5
1.53
1.5
1.75
1.79
1.94
2.16
1.11
1.76
1.54
2.49
2.19
1.06
Taste
Flavor
Color
Sweet
Pleasant
Specific
Sweet
Pleasant
Specific
Sweet
Pleasant
Specific
Salty
Pleasant
Specific
Sweet
Pleasant
Specific
After monitoring oven temperature during manufacture, quality of
different brands of biscuits were tested. Moisture content, taste,
flavor and color of biscuits were monitored. The intervals of
testing were- the day of manufacture (0 day), 14th day, 16th day and
45th day after manufacture. Butter cookies, Glucose MPP, All time,
Sugar free biscuit and Carleton biscuits were selected for these
tests. According to BDS 382 as well as in the Codex Alimentarius
Standard (1995), the maximum level of accepted moisture in
biscuits is 5. The BSTI standard of % moisture for biscuits is also
5 (Islam & Haque, 2013). All biscuits, except sugar free biscuits
had sweet taste. Sugar free biscuit had salty taste. Flavor and color
of all biscuits were pleasant and specific respectively.
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Journal of SUB 5(1): 1-12, 2014
Conclusion
The general rule is that crusty biscuits should be baked at as high a
temperature as possible. Soft dough biscuits should be baked at
lower temperatures. Increasing baking temperature with
adjustment of conveyor belt speed may reduce baking time
effectively. In the study, qualities of the raw materials were tested
and the manufacturing process and quality of different kinds of
biscuits were also studied. All flour had satisfactory moisture and
gluten level, except ACI pure had exceeded level of gluten, hence
not suitable for biscuit manufacture. Moisture content, taste, flavor
and color of all biscuit brands were found satisfactory.
Acknowledgements
Authors gratefully acknowledge the Nabisco Biscuit & Bread
Factory Ltd. For allowing to perform this work using analytical
laboratory facilities of the factory.
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