Heat Rate to a Chocolate Chip Heat Rate to a Chocolate Chip Cookie through various cooking Cookie through various cooking

SurfacesSurfaces

Date: Dec 11, 2006Date: Dec 11, 2006

Group Members:Group Members:Tony RandsTony Rands

Adrian WilliamsAdrian WilliamsJosh DustinJosh Dustin

IntroductionIntroduction

Baking is not an exact science.Baking is not an exact science. Attempting to bake items to a satisfactory condition is very difficult to Attempting to bake items to a satisfactory condition is very difficult to

say the least.say the least. The variations within oven temperature and time duration of baking The variations within oven temperature and time duration of baking

items can lead to over and under cooked items.items can lead to over and under cooked items. Those people that bake items can attest to the tediousness of Those people that bake items can attest to the tediousness of

having to stand around and check the oven every so often.having to stand around and check the oven every so often. Our goal was to find out cooking times for a chocolate chip cookie Our goal was to find out cooking times for a chocolate chip cookie

while using three different cooking surfaces:while using three different cooking surfaces: Baking StoneBaking Stone Pyrex 9x13 inch dishPyrex 9x13 inch dish Single layer stainless steel cookie sheet Single layer stainless steel cookie sheet

ObjectivesObjectives

Calculate the amount of heat transfer Calculate the amount of heat transfer from the oven coils through a from the oven coils through a baking/cooking surface into a cookie.baking/cooking surface into a cookie.

Ascertain if different cooking Ascertain if different cooking surfaces produced different cooking surfaces produced different cooking times for the chocolate chip cookietimes for the chocolate chip cookie

Setup of Heat Transfer Setup of Heat Transfer ExperimentsExperiments

Cookie dough used throughout Cookie dough used throughout experiment was made from the experiment was made from the same batch. Recipe was from same batch. Recipe was from the Better Homes and Garden the Better Homes and Garden Cook Book.Cook Book.

Oven was electric with Oven was electric with three (3) cooking shelves. three (3) cooking shelves. Our experiment used the lowest Our experiment used the lowest and the one directly and the one directly above it (20cm between shelves).above it (20cm between shelves).

Setup of Heat Transfer Setup of Heat Transfer ExperimentsExperiments

Three thermocouple units were Three thermocouple units were used to gather temperature information. used to gather temperature information.

Placement were are follows:Placement were are follows: Affixed to bottom of Affixed to bottom of

baking surface.baking surface. Embedded into cookie Embedded into cookie

dough.dough. Tied to cookie rack to record temperature of Tied to cookie rack to record temperature of

oven compartmentoven compartment

Setup of Heat Transfer Setup of Heat Transfer ExperimentsExperiments

Cookie dough specimens were shaped into Cookie dough specimens were shaped into 6cm diameter spheres. 6cm diameter spheres.

A total of six cookies were A total of six cookies were tested. One cookie per cooking tested. One cookie per cooking surface on each of the shelves surface on each of the shelves (i.e. three cooking surfaces, (i.e. three cooking surfaces, two shelves).two shelves).

The temperature was recorded every The temperature was recorded every minute until the cookies turned golden minute until the cookies turned golden brown.brown.

ExperimentExperiment

Heat radiating from the electric Heat radiating from the electric coils was captured by the baking coils was captured by the baking surface.surface.

By heat conduction through By heat conduction through the cooking surface, the cookie the cooking surface, the cookie absorbed the energy. absorbed the energy.

By free convection in the By free convection in the oven, the cookie absorbedoven, the cookie absorbedadditional energy.additional energy.

Note: The assumption was Note: The assumption was made that all energy wasmade that all energy wastransferred from the baking transferred from the baking surface to the cookiesurface to the cookie

ExperimentExperiment

The cookie dough started The cookie dough started out as a spherical shape but out as a spherical shape but during baking process the during baking process the cookie flattened out.cookie flattened out.

Initially, there was more Initially, there was more surface area exposed to heat surface area exposed to heat convection but as the cookie convection but as the cookie neared completion more surface neared completion more surface area was exposed to the cooking surface.area was exposed to the cooking surface.

Oven preheated to 375F.Oven preheated to 375F.

ExperimentExperimentThermocouple HookupThermocouple Hookup

SS SheetSS Sheet Pyrex Pyrex Baking StoneBaking Stone

ResultsResultsTime Duration and TemperaturesTime Duration and Temperatures

Pre-Heated Stone Low

Hight

Time (min)

0 1 2 3 4 5 6 7 8 9 10 11

Temp

Cookie 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

Time (min)

0 1 2 3 4 5 6 7 8 9 10 11

Temp

Cookie 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:Assumptions:

Calculations used the following:Calculations used the following: Thermal Conductivity (k). Values were based on information from class Thermal Conductivity (k). Values were based on information from class

text and internet.text and internet. Cooking stoneCooking stone 0.3 W/m*K0.3 W/m*K PyrexPyrex 1.4 W/m*k1.4 W/m*k Stainless SteelStainless Steel 16 W/m*k16 W/m*k Cookie DoughCookie Dough 0.154 W/m*k (assumed constant throughout baking 0.154 W/m*k (assumed constant throughout baking

process)process) Temperatures were average across cooking duration. Oven Temperatures were average across cooking duration. Oven

temperature fluctuated from 300F to 500F even though oven set to temperature fluctuated from 300F to 500F even though oven set to 375F. The average of the oven temperature was taken. 375F. The average of the oven temperature was taken.

Surface areas were estimated from visual inspection of cookie during Surface areas were estimated from visual inspection of cookie during process.process.

Due to the complexity of the problem, radiation is considered negligible.Due to the complexity of the problem, radiation is considered negligible.

Results (Ceramic Cooking Results (Ceramic Cooking Stone)Stone)

Heat Rate using a Ceramic Stone

0

5

10

15

20

25

30

0 2 4 6 8 10

Time (min)

He

at

Ra

te (

q)

Heat Rate onHigh Shelf

Heat Rate onLow Shelf

Results (Pyrex)Results (Pyrex)

Heat Rate for Pyrex Pan

0

5

10

15

20

25

30

35

40

0 5 10 15

Time (min)

Hea

t R

ate

(q)

in W

atts

Heat Rate onLow Shelf

Heat Rate onHigh Shelf

Results (Stainless Steel Sheet)Results (Stainless Steel Sheet)

Heat Rate on a Stainless Steel Cookie Sheet

0

5

10

15

20

25

30

35

0 2 4 6 8 10

Time (min)

Hea

t R

ate

(q)

in W

atts

Heat Rateon LowShelfHeat Rateon HighShelf

Cookie Cooking Times and Cookie Cooking Times and Amount of energy cookies Amount of energy cookies

absorbedabsorbedCooking Cooking

Time Time (min)(min)

Average Average Heat Rate Heat Rate

(W)(W)

Absorbed Absorbed Energy by Energy by Cookie (J)Cookie (J)

Ceramic Stone (Low Ceramic Stone (Low Shelf)Shelf)

1111 18.718.7 12,37112,371

Ceramic Stone (high Ceramic Stone (high shelf)shelf)

1111 20.220.2 13,66013,660

Pyrex (Low Shelf)Pyrex (Low Shelf) 99 18.918.9 10,22710,227

Pyrex (High Shelf)Pyrex (High Shelf) 1515 21.621.6 19,79219,792

Stainless Steel Sheet Stainless Steel Sheet (Low Shelf)(Low Shelf)

88 21.921.9 10,53410,534

Stainless Steel Sheet Stainless Steel Sheet (High Shelf)(High Shelf)

1111 23.623.6 15,95315,953

Conclusion/ObservationsConclusion/Observations

Cooking times average about 11 minutes over all cooking Cooking times average about 11 minutes over all cooking surfaces.surfaces.

Average heat transfer rate was 20.9 Watt for all cookies. Average heat transfer rate was 20.9 Watt for all cookies. This rate is similar to a low wattage light bulb. This rate is similar to a low wattage light bulb.

Average amount of energy absorbed by the cookie over the Average amount of energy absorbed by the cookie over the cooking time was 12,160 Joules. For comparison, a 40 Watt cooking time was 12,160 Joules. For comparison, a 40 Watt light bulb emits 26,400 Joules of energy for an 11 minute light bulb emits 26,400 Joules of energy for an 11 minute span. span.

Cookies were done when reached 212F. Note: This is the Cookies were done when reached 212F. Note: This is the boiling point of water. Once water boils off then cookie is boiling point of water. Once water boils off then cookie is done.done.

Convective coefficient decreased when the cookie’s shape Convective coefficient decreased when the cookie’s shape changed from a sphere to a flat plate. This accounts for the changed from a sphere to a flat plate. This accounts for the increase in heat rate for each cookie around minute 6. increase in heat rate for each cookie around minute 6.

Conclusion/ObservationsConclusion/Observations

Stainless Steel baking sheet showed the most Stainless Steel baking sheet showed the most amount of heat transfer. This is because the amount of heat transfer. This is because the metal conducts heat a lot better than stone or metal conducts heat a lot better than stone or glass. glass.

Cooking stones absorb heat well but release it at Cooking stones absorb heat well but release it at a slower rate.a slower rate.

Cookie completion times depended on visual Cookie completion times depended on visual inspection which was inconsistent for each inspection which was inconsistent for each cookie. cookie.

Note: Surface areas used in calculations are Note: Surface areas used in calculations are approximations.approximations. Not possible to measure this Not possible to measure this while baking was in progress.while baking was in progress.