Heat Rate to a Chocolate Chip Cookie through various cooking Surfaces

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.
• 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

3
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

4
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).

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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

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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.

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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

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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.

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ExperimentThermocouple Hookup

• SS Sheet Pyrex Baking Stone

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ResultsTime Duration and Temperatures
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Assumptions

• Calculations used the following
• Thermal Conductivity (k). Values were based on
  information from class text and internet.
• Cooking stone 0.3 W/mK
• Pyrex 1.4 W/mk
• Stainless Steel 16 W/mk
• Cookie Dough 0.154 W/mk (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.

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Results (Ceramic Cooking Stone)
13
Results (Pyrex)
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Results (Stainless Steel Sheet)
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Cookie Cooking Times and Amount of energy cookies
absorbed
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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
  cookies shape changed from a sphere to a flat
  plate. This accounts for the increase in heat
  rate for each cookie around minute 6.

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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.