1. Heat Rate to a Chocolate Chip Cookie through various cooking Surfaces Date: Dec 11, 2006 Group Members: Tony Rands Adrian Williams Josh Dustin

2. Introduction Baking is not an exact science. Baking is not an exact science. Attempting to bake items to a satisfactory condition is very difficult to say the least. 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. 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. 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: Our goal was to find out cooking times for a chocolate chip cookie while using three different cooking surfaces: Baking Stone Baking Stone Pyrex 9x13 inch dish Pyrex 9x13 inch dish Single layer stainless steel cookie sheet Single layer stainless steel cookie sheet

3. Objectives Calculate the amount of heat transfer from the oven coils through a baking/cooking surface into a cookie. 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 Ascertain if different cooking surfaces produced different cooking times for the chocolate chip cookie

4. Setup of Heat Transfer Experiments Cookie dough used throughout 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 Oven was electric with three (3) cooking shelves. Our experiment used the lowest and the one directly above it (20cm between shelves).

5. Setup of Heat Transfer Experiments Three thermocouple units were Three thermocouple units were used to gather temperature information. Placement were are follows: Affixed to bottom of Affixed to bottom of baking surface. Embedded into cookie Embedded into cookiedough. Tied to cookie rack to record temperature of oven compartment Tied to cookie rack to record temperature of oven compartment

6. Setup of Heat Transfer Experiments Cookie dough specimens were shaped into 6cm diameter spheres. Cookie dough specimens were shaped into 6cm diameter spheres. A total of six cookies were A total of six cookies were tested. One cookie per cooking surface on each of the shelves (i.e. three cooking surfaces, two shelves). The temperature was recorded every minute until the cookies turned golden brown. The temperature was recorded every minute until the cookies turned golden brown.

7. Experiment Heat radiating from the electric Heat radiating from the electric coils was captured by the baking surface. By heat conduction through By heat conduction through the cooking surface, the cookie absorbed the energy. By free convection in the By free convection in the oven, the cookie absorbed additional energy. Note: The assumption was Note: The assumption was made that all energy was transferred from the baking surface to the cookie

8. Experiment The cookie dough started The cookie dough started out as a spherical shape but during baking process the cookie flattened out. Initially, there was more 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. Oven preheated to 375F.

9. Experiment Thermocouple Hookup SS Sheet PyrexBaking Stone SS Sheet PyrexBaking Stone

10. Results Time Duration and Temperatures Pre-Heated Stone Low Hight Time (min) 01234567891011 Temp Cooki e118150160171182193199206212214218222 Stone275302310318322324325326 327335342 Air300429426424411402395387384377380407 Pre-Heated Stone High Hight Time (min) 01234567891011 Temp Cooki e103120131156182205234270236202208211 Stone296311335 334335 338367396412375 Air300400451440429418408375388400452363

11. Assumptions: Calculations used the following: Calculations used the following: Thermal Conductivity (k). Values were based on information from class text and internet. Thermal Conductivity (k). Values were based on information from class text and internet. Cooking stone0.3 W/m*K Cooking stone0.3 W/m*K Pyrex1.4 W/m*k Pyrex1.4 W/m*k Stainless Steel16 W/m*k Stainless Steel16 W/m*k Cookie Dough0.154 W/m*k (assumed constant throughout baking process) Cookie Dough0.154 W/m*k (assumed constant throughout baking process) 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. 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. Surface areas were estimated from visual inspection of cookie during process. Due to the complexity of the problem, radiation is considered negligible. Due to the complexity of the problem, radiation is considered negligible.

12. Results (Ceramic Cooking Stone)

13. Results (Pyrex)

14. Results (Stainless Steel Sheet)

15. 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) 1118.712,371 Ceramic Stone (high shelf) 1120.213,660 Pyrex (Low Shelf) 918.910,227 Pyrex (High Shelf) 1521.619,792 Stainless Steel Sheet (Low Shelf) 821.910,534 Stainless Steel Sheet (High Shelf) 1123.615,953

16. Conclusion/Observations Cooking times average about 11 minutes over all cooking surfaces. 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 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. 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. 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. 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.

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