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Lesson: Guilt-Free Chocolate

(Adapted and published with permission from Kathryn A. Hollar, Mariano J. Savelski, and Stephanie Farrell.)

Using Everyday Examples in Engineering (E3) lesson developed by Kathryn A. Hollar, Mariano J. Savelski, and Stephanie Farrell of Rowan University, with a grant from the National Science Foundation. The original E3 can be downloaded from www.engageengineering.org

Guilt-free Chocolate as Chemical Engineering

Food processing is an excellent topic to introduce chemical engineering, as students are familiar with many food products but often do not realize that chemical engineers are responsible for many of the processing and packaging steps in this industry.

In this hands-on activity designed to teach chemical-engineering principles to freshman engineering students at Rowan University, teams of high school students will melt chocolate and coat commercially available cookies, then perform several measurements and calculations. They then will write a lab report that includes nutritional labeling and recommendations for improving the chocolate-coating process.

Age range: 15 – 18 (grades 10 – 12)

Time: 1 hour for the lab; another hour of homework to write the lab report.

Learning Outcomes

Students will:

  • Understand food processing and good manufacturing protocols
  • Develop problem-solving skills
  • Perform measurements and a simple statistical analysis of data
  • Convey technical information in a lab report

Materials:

  • Glass bowls (for melting chocolate and dipping cookies)
  • Kitchen utensils (spoons, spatulas, or forks to extract dipped cookies)
  • Trays and wax paper (to hold cookies while they cool)
  • Refrigerator (for cooling cookies)
  • Microwave oven (to melt chocolate)
  • Balance (to weigh cookies)
  • Calipers (to measure size of cookies pre- and post-dipping)
  • Cookies (such as Oreos, 3-4 per team)
  • Chocolate (enough to coat the dipped cookies when melted)
  • Nutritional labels from both cookies and chocolate

Standards:

Common Core State Mathematics Standards

High School Statistics and Probablity

  • SD-2. Use statistics appropriate to the shape of the data distribution to compare center (median, mean) and spread (interquartile range, standard deviation) of two or more different data sets.
  • S-ID.3 Interpret differences in shape, center, and spread in the context of the data sets, accounting for possible effects of extreme data points (outliers).
  • S-ID.4. Use the mean and standard deviation of a data set to fit it to a normal distribution and to estimate population percentages. Recognize that there are data sets for which such a procedure is not appropriate. Use calculators, spreadsheets, and tables to estimate areas under the normal curve.

Common Core State Standards for English Language Arts/Science and Technical Literacy: Integration of Knowledge and Ideas.

R.1.11-12.7. Integrate and evaluate multiple sources of information presented in different media or formats (e.g., visually, quantitatively) as well as in words in order to address a question or solve a problem.

RST.11-12.3. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.

RST.11-12.9. Synthesize information from a range of sources (e.g., texts, experiments, simulations) into a coherent understanding of a process, phenomenon, or concept, resolving conflicting information when possible.

Introduction

At Rowan University in Glassboro, N.J., engineering freshmen are introduced to engineering principles through a two-course sequence of courses known as Freshmen Clinics. These clinics, common to all engineering majors, focus on measurements in the first semester of the freshman year.

Demonstration of engineering principles and science fundamentals through everyday processes or products engages students more in the learning process. This hands-on, minds-on approach gets students excited about engineering. It also helps narrow the gap between a high school student’s perception of what engineering is and the reality of engineering.

Chocolate Coating Experiments

Many of the engineering principles involved in the unit operations of chocolate manufacturing are too complex for high school students. However, chocolate is an ideal substance for introducing such concepts as melting point, fluid properties, good manufacturing practices (GMPs), packaging, and statistics. This simple and inexpensive experiment is appropriate for students at this level and reinforces the themes of engineering measurements, teamwork, data analysis and representation, and safety.

Activity

1. Before beginning, introduce the chocolate manufacturing process.

The chocolate manufacturing process offers a unique sequence of chemical engineering operations. These operations can be isolated to demonstrate different chemical engineering fundamentals. The raw material, cocoa beans, undergoes many different processing steps depending on the desired final products. An overview of the chocolate manufacturing process is shown in Figure 1.

Briefly, fermentation and drying of the cocoa beans is followed by shelling, roasting, and grinding to obtain a chocolate liquor which is 55 percent cocoa butter. A series of separation and mixing processes are used to obtain the final product whether it will be cocoa butter, cocoa powder, or other consumer products such as milk or dark chocolate.

cocoa processing

Figure 1: Overview of chocolate manufacturing process.

This vintage video follows chocolate from Aztec time through growing and processing into chocolate:

[youtube]http://www.youtube.com/watch?v=Tez9RZZIwC8[/youtube]

2. Ask student teams to speculate on characteristics of the equipment required for each unit operation and if possible draw analogies between common household appliances and industrial equipment.

Ask student teams to list food handling considerations in their own homes. Their responses are used as the basis for a class discussion of how these basic principles are implemented on an industrial scale, or GMP.

3. At the conclusion of the discussion, provide each team with several (3 to 4) cookies of the same kind, such as Oreos.

4. Have students use calipers and balance scale to record the size and weight of each cookie and calculate the average and the standard deviation.

5. Using a microwave, melt the chocolate. Have students dip-coat the cookies then cool them in the refrigerator.

6. Once the cookies cool, have students record the size and weight of each coated cookie, and calculate the same statistical parameters.

7. Have students use these data to calculate an average coating thickness and recalculate a nutritional label.

To calculate a new nutritional label, students must convert the fat, protein, carbohydrate, and calorie information for the chocolate and the cookie to a per gram basis, then determine the contribution of the cookie and chocolate coating each category.

8. While cookies are cooling, have student teams work to propose a method for calculating each quantity. Each team briefly presents their method, providing a simple context for discussing problem-solving.

Using the calculated average value for the coated cookie and the information in Figures 2 and 3,  ask student teams to recalculate a nutritional label for a serving size of 2 cookies based on the knowledge that each gram of fat contains 9 calories, each gram of protein contains 4 calories, and each gram of carbohydrate contains 4 calories.

The students’ new label must include grams and percent daily values of total fat, saturated fat, cholesterol, sodium, total carbohydrates, dietary fiber, sugars, and proteins, as well as percent daily values of vitamin A, vitamin C, iron, and calcium.

oreo label

Figure 2: Nutritional label for Oreo cookies

chocolate label

Figure 3: Label for semi-sweet chocolate

Do the numbers add up?

Students may find that there are some discrepancies in the labels presented to them; for instance, the sum of the calories from total carbohydrates, fat, and protein do not equal the available calories stated on the label. Student teams must propose possible reasons for this discrepancy, and incorporate this in their discussion in the report. This exercise and the statistical analysis of final cookie weight and coating thickness introduce the issue of quality control and packaging.

Students calculate average values for the nutritional label, and must decide which cookies to reject using the standard deviation.

Report

Student teams must submit a report a week after completing the lab. The reports should contain the following information:

  1. An introduction explaining the objectives of the experiment and some background on chocolate.
  2. Brief materials and methods, including some commentary on GMPs
  3. Results and data analysis section in which a recalculated nutritional label and statistical analysis is presented. A brief explanation of the team’s method for recalculating the nutritional label, as well as some commentary on possible reasons for any trends observed should be included in this section.
  4. Conclusions and recommendations section that includes some discussion on how to make the chocolate coating process more consistent.
  5. An appendix with raw data and sample calculations.

Extensions:

If the lab period permits, students can investigate the effect of power input of the microwave, fat composition of the chocolate, and mixing on melting time.

Extensions:

If the lab period permits, students can investigate the effect of power input of the microwave, fat composition of the chocolate, and mixing on melting time.

Additional resources:

The Sweet Lure of Chocolate. The San Francisco Exploratorium’s history of chocolate, including an activity on “tempering” or melting and cooling chocolate so it will have that delicious snap.

Read about CSI – Chocolate Science Investigations – the University of Colorado, Colorado Springs STEM camp for students in grades 8 – 12.

Cadbury’s  design and technology area includes information on chocolate manufacturing and an interactive game that lets students try their hand at being a new product development manager.

The American Chemical Society has an engaging activity on the science and chemical engineering of why chocolate melts in your mouth and other marvels.

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