Note: Descriptions are shown in the official language in which they were submitted.
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A method of baking and an oven
Field of the invention
The invention relates to a baker's oven and in particular to the operation of
the oven.
Background of the invention
A conventional baker's oven comprises a number of stacked oven compartments
with
individual oven doors at the front. Each level of the oven includes two side
by side
compartments which each have a fixed shelf onto which baking trays or bread
pans or a
like can be loaded.
The oven compartments are heated by electric heating elements mounted bottom
and
top of each compartment. The heating elements are formed as single heating
units
comprising a number of parallel arms connected in series by U-shaped elements.
The
parallel arms extend from the oven door to the rear of the compartment and are
spaced
across the width of the oven.
The top and bottom heating elements can be separately controlled to vary the
heat
distribution within the oven. For certain types of baked goods, it is
advantageous to
supply the heat predominantly from the bottom of the oven. The bottom heating
elements of conventional baker's ovens are usually more or less uniformly
distributed
over the floor of the oven to provide a uniform distribution of heat within
the oven.
According to conventional baking practice, it is important that a constant
temperature is
maintained throughout the baking cycle, thus preheating the oven, or allowing
the oven
to cool, prior to loading with product is important. Typically the oven
temperature must
be kept within 10 C of an ideal temperature.
It is known to use a timer to activate the oven prior to the arrival of the
baker at the start
of the day, so that the oven is preheated when the baker arrives. While the
use of a
timer effectively presents an oven at a predetermined temperature at a time
set many
hours earlier, there are risks (e.g. of fire) associated with activating
unattended ovens.
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Commercially available Multi-deck, Setter ovens, and other such ovens with
multiple
baking chambers within one chassis, may be capable of baking many different
products
at the same time. However, it is commercially accepted that these ovens need
to be
pre-heated to, or above recipe temperature before loading each product. As
there is no
fan assistance in most conventional ovens, the heat is typically difficult to
control, and
the baker must often be familiar with each oven's characteristics to achieve
acceptable
results.
Different bakery products require different baking temperatures. Therefore the
baker's
production schedule is complicated, and the oven utilisation is reduced, by
having to
pre-heat/pre-cool an oven prior to baking. The production schedule must be -
changed so
that the oven temperature closely matches the requirements of the next product
to be
loaded. In busy bakeries, there is often the need to break the usual
production cycle
(due to rejected product, unexpected orders etc.) and there is also the issue
of
inexperienced staff needing to run ovens at short notice. Even for the most
experienced
operator, the issues involved in obtaining the most efficient production
schedule, is often
at odds with what the store's customer's demand for fresh full variety of
product.
A particular problem with controlling oven temperature is "heat over-run".
Heat over-run
stems from the thermal inertia of the heating system. Typically the heating
elements are
much hotter than the air in the oven. Heat is thereby transferred from the
elements to
the air and is in turn transferred to the bakery product in the oven. Heat
over-run occurs
after the oven is unloaded and the bakery product is removed. After the bakery
products
are removed, even if the heating elements are deactivated, heat stored within
the
elements is transferred to the air within the empty oven. This results in a
very hot oven.
This heat is not only wasted but results in considerable inefficiency in that
the oven may
well be too hot for the next batch of products to be loaded meaning that the
oven must
then be precooled for the next batch. One approach to the issue is to
gradually reduce
the power to the heating elements as the oven air temperature approaches a
required
baking temperature. This means that the elements are not as hot as they might
be when
the oven is unloaded.
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Objects of the present invention include to reduce oven preheating/precooling
requirements or at least provide alternatives to existing arrangements in the
marketplace.
Summary of the invention
According to the invention, there is provided a baker's oven including:
supporting means for supporting one or more baking trays;
heating means arranged to underlie the baking trays to provide a substantial
proportion of the heat to the baking trays than to other portions of the oven;
a temperature sensor for providing a signal indicative of oven temperature;
an interface adapted to receive information from a baker indicative of a bake
program and information indicative of products being loaded into the oven;
control means operatively connected to the heating means, the temperature
sensor and the interface; and
the control means being adapted to deactivate the heating means after a first
predetermined portion of a fixed baking time in response to the oven
temperature
reaching a trip temperature.
"Baking time" as used herein refers to the baking time experienced by the
product.
Typically the baking time commences with product being loaded into the oven
and
finishes with the issuance of a signal from an indicator means indicative of
the end of
the cycle (in response to which a baker should remove the product from the
oven). The
product could be retarded or proofed in a cold oven for a period of time (e.g.
overnight).
The baking time would then commence with the activation of the heating means.
The information indicative of a bake program might simply be the required
baking time
and a desired temperature (e.g. the trip temperature). Alternatively, the
information
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might simply be an indicator of product type, the control means being
configured to
calculate the trip temperature and baking time based on the product type.
The control means may be adapted to deactivate the heating means after a
second
predetermined portion of the baking time independently of the oven
temperature.
Preferably the control means is configured to thermostatically control the
heating
means. For example the heating means may be thermostatically controlled to
maintain
the trip point temperature.
The first predetermined portion is preferably between 80% and 90%, and most
preferably about 85%, of the baking time. The second predetermined portion is
preferably about 95% of the baking time.
The trip temperature may be preselected to be about 10 degrees below a high
set
temperature, the high set temperature being the highest maximum temperature
the
oven should reach at any time. This temperature is determined by trial and
error with
the highset temperature being the highest baking temperature of the oven to
yield
acceptable product.
According to another aspect of the invention there is provided a method of
operating the
baking oven including a heating means arranged to underlie baking trays
whereby a
substantial proportion of the heat is provided to the baking trays, the method
including
the steps of heating the heating means according to a bake program indicative
of
products loaded into the oven, and deactivating the heating means after a
first
predetermined portion of a fixed baking time in response to the oven reaching
a trip
temperature.
The heating means and the supporting means are preferably relatively moveable
to
reduce the incidence of localised burning of product on the baking trays
proximal the
heating means.
The supporting means may include a carousel rotatable about a vertical axis.
The
interior of the oven is preferably substantially free of high thermal inertia
objects, such
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as bulk ceramic material and plate metal fittings, to minimise thermal inertia
of the oven
interior and thereby improve baking conditions. This ensures that a large
proportion and
preferably substantially all of the heat supplied by the heating elements
arranged
according to the invention is supplied directly to productively produce
product rather
5 than heating objects which store and radiate heat.
Brief description of the drawings
Figure 1 is a sectional side view of a five level rotary baker's oven in
accordance with an
embodiment of the present invention;
Figure 2 is a sectional plan view showing one level of a previously disclosed
oven; and
Figure 3 is a sectional plan view of one side of one of the levels of the oven
of Figure 1
showing the heating elements and the baking trays.
Description of the preferred embodiments
It has been discovered that by concentrating the active portions of the
heating elements
more directly under the baking trays the quality of baked goods and the
operation of the
baking oven can be improved. This has been found to be associated with
supplying the
heat more directly to the product.
According to an aspect of the invention not expressly claimed herein, there is
provided a
baking oven having heating elements arranged to underlie baking trays to
provide a
substantial proportion and preferably substantially all of the heat to an
active region
under the baking trays than to an inactive region positioned outwardly of the
active
region.
The oven chamber preferably includes heating elements extending from a wall of
the
oven into the active region, each element having an inactive portion and an
active
portion, the inactive portion extending from the wall to the active portion
which extends
within the active region for more directly heating the underside of the baking
trays.
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In an advantageous arrangement, the oven includes a rotatable turntable for
supporting
the baking trays. In this instance the active region may be defined by an
outer most
periphery of the baking tray as it is rotated on the turntable. Alternatively
the active
portions of the elements may lie within a region defined by an inner most
portion of the
outer periphery of the baking trays as they are rotated on the turntable.
Preferably the
baking trays define a rectangle centred on an axis of rotation of the carousel
and the
active region boundary is defined as being located between, and most
preferably half
way between, a circle defined by rotation of an outer most corner of the
rectangle and a
circle defined by rotation of the nearest approach of an edge of the rectangle
about the
axis.
Preferably the heating elements are arranged to provide more than 2 times,
preferably
2.5 to 3.5, and most preferably 2.9 to 3.1, times greater power density to the
active
region than to the inactive region.
Preferably the heating elements are relatively narrow thereby allowing the
heating
elements to be more densely concentrated within the active region. Each
heating
element may include two elongate heating element portions, a steam generation
chamber positioned intermediate and operably connected to the elongate heating
element portions and having at least one steam outlet.
Referring to Figures 1 and 2, the baker's oven is a rotary oven 10 similar to
the type
sold under the registered trade mark "ROTEL". In the embodiment illustrated,
the oven
has five levels with two oven compartments 11 on each level. A drive motor 12
(not
shown) is operably connected to a pair of vertical shafts 13 on which are
mounted
turntables 14 which may incorporate optional ceramic "tiles" 15 on which the
baking
trays (not shown) are cooked. Each oven compartment 11 has an oven door 16
operably openable and closable by a handle 17.
Each oven compartment 11 has top heating elements 18 mounted to the underside
of
the top wall 19 of the oven compartment 11. As shown in more detail in Figure
3, each
oven compartment 11 has a pair of substantially U-shaped inner heating
elements 20
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mounted on the bottom wall 19a. The operation of the heating elements 20 is
controlled
by a computerised control system (not shown).
By selectively energising the upper heating element 18 and the lower heating
element
20 it is possible to control:
1. The air temperature within the oven chamber,
2. The heat rising directly from the'lower heating element 20 to the bottom of
the
turntable 14 and thus the baking trays 30, and
3. The heat radiating from the upper heating elements 18.
For example by supplying more electrical power to the lower element 20, it is
possible to
supply more heat to the bottom of the turntable 14 and thus baking trays 30.
This could
be used to produce, for example, a bread having more bottom crust and a darker
baked
colour on top.
It has been found that the position of the heating elements has a large
bearing on the
quality of the baked product. This is thought to be related to the control
over the
application of heat to the lower surfaces of turntable 14 and baking trays 30.
By
concentrating the heating elements under the baking trays, it is possible to
provide a
more concentrated heat to the underside of the turntable 14 and baking trays
30 and
thereby have greater control over the above listed variables. The result is a
baking oven
which can be used to produce an improved baked ptoduct.
Figure 3 shows a cross sectional plan view of one side of the oven of Figure
1. It shows
a potential layout of the heating elements 20 and the relative positioning of
the baking
trays 30 when in use. The turntable 14 is omitted from this view for clarity.
As illustrated
the heating elements 20 are relatively narrow elongate members. This allows
the
heating elements 20 to be more closely spaced and positioned under the baking
trays
30. Only three elements 20 are illustrated here for clarity although of course
it is
possible to use more. This concentration of heating elements differs from
conventional
thinking which would have a number of widely spaced heating element portions
evenly
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distributed across the oven floor to produce a more even distribution of heat
throughout
the baking chambers.
As illustrated in Figure 2, previously disclosed ovens have widely spaced
heating
elements evenly spread across the baking chamber 11 including providing
heating
element portions 23 close to peripheral wall 14.
To give an idea of scale, each baking tray 30 is about 18 inches (460 mm) by
about 30
inches (720mm) and the trays are spaced by the shaft 30 which is about 1 inch
(25mm)
thick. Thus the two trays being spaced by the shaft 13 define a rectangle of
about 37
inches (940mm) by about 30 inches (720mm). This tray size is commonly used in
Victoria (a region of Australia). Elsewhere in Australia 405mm x 737mm is a
common
tray size. Trays as large as 460mm x 762mm are sometimes used.
Each heating element 20 is provided with an inactive portion 21 and an active
portion
22. The inactive portion 21 does not produce heat. The active portion 22
produces heat.
The heating element extends from a wall 120 of the oven with the inactive
portion 21 of
the heating element providing an inactive region of the oven. The active
portion 22 of
the heating element extends from the inactive portion 21 into the active
region of the
oven beneath the baking trays 30. The active portions have a more or less
homogenous
construction, but have been found to produce little or no heat along a length
of 25mm of
so adjacent the inactive portions 21.
It has been found that an improved distribution of heat within the baking
chamber can
be achieved by positioning the active portions 22 within the region 40
described by the
outer most corner 31 of the baking trays as it is rotated about the shaft 13.
This region is
herein referred to as the active region. The shorter heating element 20 is
arranged so
that the active portion 22 lies predominantly within a smaller active region
41. The
smaller active region 41 is defined by the nearest approach of the farther
surfaces 31 of
tray 30 to the shaft 13 as it is pivoted about shaft 13. Innermost active
region 42 is
defined by the inner most approach of edge 32 of trays 30 as it rotates around
shaft 13.
The positioning of the active portions 22 within this innermost active region
42 means
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that the active regions are always directly underneath the baking tray as it
is rotated
about shaft 13.
The ideal location of the boundary 140 between the active region and the
inactive
region is calculated with respect to the nearest and furthest approaches
(relative to the
central axis 13) of the edge 31, which correspond to the circles 40, 41, such
that
boundary 140 is halfway between circles 40, 41. Power densities of 0.133 W/cm2
and
0.4 W/cm2 in the inactive and active regions respectively have been found to
be ideal.
Table 1
Process Scenario 1 Scenario 2
High oven air temp bake Low oven air temp bake
Oven temp before load (0 min) 230 200
Oven temp after load (0 min) 210 170
Oven temp after (10 min) 220 (at trip point) 190
Oven temp after (20 min) 220 (at trip point) 205
Oven temp at 85% of bake time (25.5 min) 220 (all heating off) 210
Oven temp at 90% of bake time (27 min) 218 212
Oven temp at 95% of bake time (28.5 min) 216 216 (all heating off)
Oven temp at unload (30 min) 214 214
Oven temp after unloading (30 min) 228 228
Table 1 illustrates the operation of the oven according to a preferred form of
the
invention. In this example the bakery product is sandwich bread for which a
baking time
of 30 min and high set temp of 230 C have been determined through trial and
error on
this type of oven to be sufficient to produce acceptable product. Two possible
scenarios
are shown. In scenario I the oven is initially relatively hot. Scenario 2
shows an initially
cooler oven.
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In both scenarios a trip point temperature of 220 C, i.e. 10 C less than the
high set
temp, is determined. About 30 C of heat is lost from the oven upon loading.
The oven is
then thermostatically controlled to maintain, or at least attempt to maintain
the trip point
temperature.
5 In scenario 1, starting out with a relatively hot oven, the oven cools and
reaches trip
point temperature 220 C after 10 min. Thereafter the heating elements are
thermostatically controlled to cycle on and off to maintain this temperature.
Having
reached trip point temperature, the elements are deactivated at 85% of the
baking time,
i.e. 25.5 minutes. Having cycled on and off between 10 and 25.5 minutes, the
heating
10 elements in this scenario are active for a total 23 minutes out of the 30
minute baking
time.
In scenario 2, starting with a cooler oven, the heating elements operate
continuously but
the oven does not reach trip point temperature. The heating elements are
deactivated at
95% of the baking time, i.e. 28.5 minutes.
In both scenarios the bread continues to bake after deactivation of the
elements.
Residual heat within the oven, including heat stored in the elements is thus
absorbed.
As a result, upon unloading, the elements are much cooler than they might
otherwise
be, and heat over-run is substantially reduced. In both scenarios, the heat
over-run is
only 14 C (i.e. 214 C to 228 C) so that a like batch of bread can be
immediately loaded.
Both scenarios produce satisfactory bread, indeed the product is essentially
indistinguishable.
The method of operating and controlling the heating elements is preferably
implemented
using electronics and software incorporated into the oven.
The preferred operation of the oven is as follows:
The baker selects the product to be baked, from a menu that is presented as a
product
name, product category, or as a simple product code or number. These can be
presented on the control panel screen as pictures, drawings, or just
descriptive names
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or numbers. In response to the product selection, the controller 61 determines
the trip
temperature and baking time.
Once selected, program lock-outs that will stop the program operating are
"MINIMUM
LOAD TEMPERATURE" and "MAXIMUM LOAD TEMPERATURE" that may be specific
to each product, or sometimes product type. A thermocouple 62 inside the oven
chamber is read at regular intervals by the software, and so, for example, an
oven
chamber that is read as at 120 degrees C, will reject any program for products
with a
"MINIMUM LOAD TEMPERATURE" above 120 degrees. There may be many products
that can bake and produce acceptable product from as low as 20 degrees C,
ranging up
to 119 degrees C, and any of these can be loaded without lock-out occurring.
Once the program product has been accepted the interface 60 will flash a
message
"LOAD PRODUCT". Once loaded, the baker presses the "BAKE START" button, and
the elements are thermostatically operated by power source 63 to maintain the
trip
temperature.
As heat is supplied directly to the product from elements on the oven floor
and oven
roof, it is possible to provide more or less top heat, or bottom heat to the
product, so as
to ensure that, for example, product with a thicker bottom material, than top
material,
will have the thicker material bake at the same time, by simply increasing
bottom
element power, and reducing top element power.
The concentration of heating elements in the active region is thought to allow
a more
directed application of heat to the baking trays, thereby reducing product
burning as a
result of excessive oven temperature. The relative motion of the carousel has
been
found to reduce burning of products overlying the elements.
It will be understood that the invention disclosed and defined in this
specification
extends to all alternative combinations of two or more of the individual
features
mentioned or evident from the text or drawings. All of these different
combinations
constitute various alternative aspects of the invention.
