Heat Rate to a Chocolate Chip
Cookie through various cooking
Surfaces
Date: Dec 11, 2006
Group Members:
Tony Rands
Adrian Williams
Josh Dustin
Introduction
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Baking is not an exact science.
Attempting to bake items to a satisfactory condition is very difficult to
say the least.
The variations within oven temperature and time duration of baking
items can lead to over and under cooked items.
Those people that bake items can attest to the tediousness of
having to stand around and check the oven every so often.
Our goal was to find out cooking times for a chocolate chip cookie
while using three different cooking surfaces:
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Baking Stone
Pyrex 9x13 inch dish
Single layer stainless steel cookie sheet
Objectives
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Calculate the amount of heat transfer from
the oven coils through a baking/cooking
surface into a cookie.
Ascertain if different cooking surfaces
produced different cooking times for the
chocolate chip cookie
Setup of Heat Transfer
Experiments
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Cookie dough used throughout
experiment was made from the
same batch. Recipe was from
the Better Homes and Garden
Cook Book.
Oven was electric with
three (3) cooking shelves.
Our experiment used the lowest
and the one directly
above it (20cm between shelves).
Setup of Heat Transfer
Experiments
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Three thermocouple units were
used to gather temperature information.
Placement were are follows:
 Affixed to bottom of
baking surface.
 Embedded into cookie
dough.
 Tied to cookie rack to record temperature of oven
compartment
Setup of Heat Transfer
Experiments
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Cookie dough specimens were shaped into 6cm
diameter spheres.
A total of six cookies were
tested. One cookie per cooking
surface on each of the shelves
(i.e. three cooking surfaces,
two shelves).
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The temperature was recorded every minute
until the cookies turned golden brown.
Experiment
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Heat radiating from the electric
coils was captured by the baking
surface.
By heat conduction through
the cooking surface, the cookie
absorbed the energy.
By free convection in the
oven, the cookie absorbed
additional energy.
Note: The assumption was
made that all energy was
transferred from the baking
surface to the cookie
Experiment
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The cookie dough started
out as a spherical shape but
during baking process the
cookie flattened out.
Initially, there was more
surface area exposed to heat
convection but as the cookie
neared completion more surface
area was exposed to the cooking surface.
Oven preheated to 375F.
Experiment
Thermocouple Hookup
SS Sheet
Pyrex
Baking Stone
Results
Time Duration and Temperatures
Pre-Heated
Stone Low
Hight
Temp
0
1
2
3
4
5
6
7
8
9
10
11
Cooki
e
118
150
160
171
182
193
199
206
212
214
218
222
Stone
275
302
310
318
322
324
325
326
326
327
335
342
Air
300
429
426
424
411
402
395
387
384
377
380
407
Pre-Heated
Stone High
Hight
Temp
Time (min)
Time (min)
0
1
2
3
4
5
6
7
8
9
10
11
Cooki
e
103
120
131
156
182
205
234
270
236
202
208
211
Stone
296
311
335
335
334
335
335
338
367
396
412
375
Air
300
400
451
440
429
418
408
375
388
400
452
363
Assumptions:
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Calculations used the following:
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Thermal Conductivity (k). Values were based on information from class
text and internet.
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Cooking stone
Pyrex
Stainless Steel
Cookie Dough
process)
0.3 W/m*K
1.4 W/m*k
16 W/m*k
0.154 W/m*k (assumed constant throughout baking
Temperatures were average across cooking duration. Oven
temperature fluctuated from 300F to 500F even though oven set to
375F. The average of the oven temperature was taken.
Surface areas were estimated from visual inspection of cookie during
process.
Due to the complexity of the problem, radiation is considered negligible.
Results (Ceramic Cooking Stone)
Heat Rate using a Ceramic Stone
30
Heat Rate (q)
25
20
15
Heat Rate on
High Shelf
10
Heat Rate on
Low Shelf
5
0
0
2
4
6
Time (min)
8
10
Results (Pyrex)
Heat Rate for Pyrex Pan
40
Heat Rate (q) in Watts
35
30
25
Heat Rate on
Low Shelf
20
15
Heat Rate on
High Shelf
10
5
0
0
5
10
Time (min)
15
Results (Stainless Steel Sheet)
Heat Rate on a Stainless Steel Cookie Sheet
Heat Rate (q) in Watts
35
30
25
20
Heat Rate
on Low
Shelf
Heat Rate
on High
Shelf
15
10
5
0
0
2
4
6
Time (min)
8
10
Cookie Cooking Times and Amount
of energy cookies absorbed
Cooking
Time (min)
Average
Heat Rate
(W)
Absorbed
Energy by
Cookie (J)
Ceramic Stone (Low Shelf)
11
18.7
12,371
Ceramic Stone (high shelf)
11
20.2
13,660
Pyrex (Low Shelf)
9
18.9
10,227
Pyrex (High Shelf)
15
21.6
19,792
Stainless Steel Sheet (Low
Shelf)
8
21.9
10,534
Stainless Steel Sheet (High
Shelf)
11
23.6
15,953
Conclusion/Observations
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Cooking times average about 11 minutes over all cooking surfaces.
Average heat transfer rate was 20.9 Watt for all cookies. This rate
is similar to a low wattage light bulb.
Average amount of energy absorbed by the cookie over the cooking
time was 12,160 Joules. For comparison, a 40 Watt light bulb emits
26,400 Joules of energy for an 11 minute span.
Cookies were done when reached 212F. Note: This is the boiling
point of water. Once water boils off then cookie is done.
Convective coefficient decreased when the cookie’s shape changed
from a sphere to a flat plate. This accounts for the increase in heat
rate for each cookie around minute 6.
Conclusion/Observations
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Stainless Steel baking sheet showed the most amount of
heat transfer. This is because the metal conducts heat a
lot better than stone or glass.
Cooking stones absorb heat well but release it at a
slower rate.
Cookie completion times depended on visual inspection
which was inconsistent for each cookie.
Note: Surface areas used in calculations are
approximations. Not possible to measure this while
baking was in progress.