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Heat Rate to a Chocolate Chip Cookie through various cooking Surfaces. Date: Dec 11, 2006 Group Members: Tony Rands Adrian Williams Josh Dustin. Introduction. Baking is not an exact science. Attempting to bake items to a satisfactory condition is very difficult to say the least.
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Heat Rate to a Chocolate Chip Cookie through various cooking Surfaces Date: Dec 11, 2006 Group Members: Tony Rands Adrian Williams Josh Dustin
Introduction • 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: • Baking Stone • Pyrex 9x13 inch dish • Single layer stainless steel cookie sheet
Objectives • 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 • 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 • 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 • 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). • The temperature was recorded every minute until the cookies turned golden brown.
Experiment • 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 • 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.
ExperimentThermocouple Hookup SS Sheet Pyrex Baking Stone
Assumptions: • Calculations used the following: • Thermal Conductivity (k). Values were based on information from class text and internet. • Cooking stone 0.3 W/m*K • Pyrex 1.4 W/m*k • Stainless Steel 16 W/m*k • Cookie Dough 0.154 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. • Surface areas were estimated from visual inspection of cookie during process. • Due to the complexity of the problem, radiation is considered negligible.
Conclusion/Observations • 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 • 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.
