Dr. Skip's Corner: K-12 Teaching Adventures @ OSU Engineering
October 2004

Engineering Analysis of Tea Brewing -- A Leaching Process

Skip Rochefort, Ellen Momsen, and Tom Thompson (Philomath HS)

The Science and Engineering of Brewing Tea:
Engineering Science for Middle School through High School –
Connecting the Science to the Engineering

At the annual meeting of the Oregon Science Teachers Association (OSTA) on October 8, the OSU College of Engineering was on hand to highlight our K-12 outreach and Women & Minorities in Engineering programs. We held several workshops for middle and high school teachers that demonstrated how to bring ENGINEERING into the classroom. Many of the activities currently used by physical and life science teachers can be extended to include an "engineering approach" to scientific inquiry, or what engineers call "problem solving.” Most of the topics covered in this column each month – making ice cream, chemical-powered cars, gels in daily life, super absorbent polymers, etc. – not only introduce students to Engineering Science, but also can be used to satisfy the requirements for experimental design, analysis, and interpreting results of the CIM 10th grade benchmark. One of the engineering science examples presented at the OSTA meeting was, “Brewing Tea: An Engineering Leaching Process.” Most everyone has either brewed tea or watched someone brew tea, so this is an example that everyone can relate to. How do we make this an engineering science or scientific inquiry example, you might ask? Read on for all the exciting details!

ENGINEERING SCIENCE CLASSROOM TOPIC
Science, Engineering, and Tea Extraction

Introduction by Tom Thompson, Philomath High School
The tea extraction lab illustrates the connection between science and engineering in the classroom. The following CIM benchmark in physical science relate to the content of this lab:

Analyze the effects of various factors on physical changes and chemical reactions.

In this case, we are looking at a physical change with the leaching of water-soluble solutes in tea using water as a solvent. The process of leaching is important to a variety of chemical systems. Leaching removes nutrients from soil. It is responsible for natural toxic minerals finding their way into the ground water. It is also valuable in removing toxins as is described in the attached paper.

The paper not only describes the chemistry of the leaching process in its introduction, but it also illustrates the connections between science and engineering. The science in the paper involves investigating the solubility of a toxic compound from velvet beans. In this case, the authors are testing well-known scientific claims about leaching under lesser-known conditions. When the authors start discussing the process of extracting the chemical so that 99% is removed they are talking about engineering. In this case, the science of leaching and a specific investigation of leaching help engineers design a process for removing 99% of the toxic chemicals. In this case, engineering provides a context for doing science.

The engineering problem in the tea lab is to design a process to leach tea while keeping down the energy costs and brewing time. In order to design the process, chemical engineers would need to know something about the leaching of tea under different conditions of temperature and time. The scientific claims that could be tested are:

  1. Concentration of water-soluble chemicals is dependent on temperature because chemicals tend to become more soluble at higher temperatures.
  2. Concentration of water soluble chemicals will change over time since they will have to diffuse from the inside of the pieces of tea to the water on the outside.

The engineering takes place when the scientific data is used to design an optimum temperature and time for brewing. Most likely the company that wants to make large batches of brewed tea will want to keep the temperature down to reduce energy costs but keep the time short to increase capacity.

ENGINEERING SCIENCE CLASSROOM TOPIC
Engineering Analysis of Tea Brewing -- A Leaching Process
Dr. Skip Rochefort, Chemical Engineering Department, Oregon State University

BACKGROUND
In chemical engineering terms, the process of extracting a solute from a solid using a solvent is called leaching. The process of leaching will be studied using one of the oldest experiments known to humankind: the process of brewing tea. The leaching of tea from tea leaves can be accomplished in a number of ways, but the most common is to bring the liquid (water) in contact with the tea leaves under controlled temperature conditions. The water temperature typically varies from near room temperature (so called "sun tea") to near the boiling point (hot tea). The rate at which the leaching occurs is a strong function of the leaching water temperature.

You have just been hired by the LIPTON TEA Co. as a process engineer. Your first assignment is to design a process for brewing tea that the company will use in its fast growing bottled tea market. The first step is to design a simple laboratory experiment that will provide your engineering team with a set of data that an engineer could use to design an "efficient" process for brewing tea.

Your design parameters should be to maximize production rate and minimize operating costs (i.e., energy), while maintaining product quality.

PROJECT DESCRIPTION
Experimental Design
  • 
Design an experiment to acquire data that will give you the information needed to accomplish the given task (tea process design).

    Experimental Materials (available to students)
    • tea bags, thermometer and thermocouple
    • Pasteur pipette (3ml glass) and plastic pipette (10ml); pipetter (plunger type).
    • graduated cylinder (10 or 25ml),
    • beakers ( 250 ml or similar), styrofoam cups, plastic coffee mugs with lids.
    • sample collection vials (approx. 15ml) with caps (10 vials)
    • heater/stirrer plate and magnetic stir bars

Project Planning (groups of 3 students)
   
1) Write-up a preliminary experimental plan and clear it with your teacher.

    Questions to think about in planning experiments:
    • What are the important parameters to measure (concentration, temp., time)?
    • What is the temperature range of interest?
    • How does one obtain samples?
    • How will the concentration of tea be determined? Is an "absolute concentration" needed or is a "relative concentration" sufficient? HINT: Think about developing a calibration curve using "tea standards

   2) Perform some "preliminary experiments" to establish the parameters for a well-designed experiment, to be completed in the next laboratory session.
   3) RECORD and SHARE DATA with GROUP MEMBERS

ENGINEERING SCIENCE CLASSROOM TOPIC
Engineering Analysis of Tea Brewing -- A Leaching Process

SUGGESTIONS for HIGH SCHOOL CIM 10th Grade Project
Calculations, Data Analysis, and Process Design

1) Using EXCEL, do the following:

  1. LIST all the leaching data of solution concentration as a function of leaching time at each temperature (referenced to the tea standard given in lab as Co=1.0)
  2. Graph ALL the concentration vs. time data at the various temperatures on a SINGLE plot. Use different symbols for each temperature and make certain that the legend properly identifies the temperature data (NOT "series 1", "series 2", etc.).

2) Identification of a time constant(tL) for the leaching process as a function of temperature.

In any process which is rate limited by temperature (such as tea brewing) it is possible to identify a characteristic time for the process, usually called the time constant(tL) for the process.

For the tea brewing process studied in the laboratory, we will identify the time constant(tL) as that time at which the concentration has reached 50% of the final concentration .

The smaller the value of the time constant (tL), the faster the process.

    Using EXCEL:
  1. LIST the time constant(tL) vs. temperature data in your spreadsheet.
  2. PLOT the time constant (tL) vs. temperature for your experimental data.

3) You have just been hired by the LIPTON TEA Co. as a process engineer. Your first assignment is to design a process for brewing tea which the company will use in its fast growing bottled tea market. From all the laboratory experiments you have performed, you now have a set of data which a chemical engineer could use to design an "efficient" process for brewing tea.

Your design parameters should be to maximize production rate and minimize operating costs (i.e., energy), while maintaining product quality. What would be your recommendations for the operating conditions of the tea brewing process? EXPLAIN your recommendations so that the company’s engineering review board will be convinced you are correct (i.e., SELL your process design to the review board).

ENGINEERING SCIENCE CLASSROOM TOPIC
Engineering Analysis of Tea Brewing -- A Leaching Process

General Comments and Proposed Class Schedule (may be modified)
NOTE: Each “Session” designates a 1 hr 50min class period

    Session 1
  1. Problem (project) statement and assignment of groups (typically 3 people).
  2. Preliminary experimental design – group brainstorming .
  3. Preliminary experiments – collect data from simple experiments
  4. HW Assignment – each student develops an experimental plan based on preliminary experiments for the next class session.
    Session 2
  1. Group develops “revised experimental plan” based on individual plans.
  2. Class discussion – groups share their experimental plan.
  3. Group develops “revised experimental plan #2” based on class discussion.
  4. Groups begin implementation of experimental plan.

Session 3
LAB SESSION – groups implement experimental plan.

    Session 4
  1. Data Analysis and Interpretation – use of spreadsheet program (Excel) for plotting data.
  2. Collect “missing data” as needed.
  3. HW Assignment – each student (or group) analyzes experimental results and prepares data tables and plots. Propose an “optimum process design” based on constraints – minimize time and energy.
    Session 5
  1. Group presentation of results -- Classroom discussion.
  2. Class proposes the “optimum design for the tea brewing process”.