National Agricultural Literacy Curriculum Matrix
Milk: The Scoop on Chemical and Physical Changes
9 - 12
In this lesson students apply their knowledge of physical science to dairy products to determine if the changes that take place when turning milk into cheese, butter, yogurt, ice cream, whip cream and other dairy products, is a physical or chemical change.
- Dairy Products-Chemical or Physical Change handout, 1 copy per class
- Internet access for each group of students
- Milk Products graphic
- The Milk Pasteurization Process infographic
Essential Files (maps, charts, pictures, or documents)
chemical change: a change that results in the formation of a new chemical substance through the making or breaking of bonds between atoms
physical change: a change that occurs without altering the chemical composition of a substance.
Did you know? (Ag Facts)
- It takes approximately 2 and 1/2 gallons of milk to make 1 pound of butter.2
- It takes approximately 1 gallon of milk to make 1 pound of cheese.2
- The average cow in the United States produces 6-8 gallons of milk per day.3
Background Agricultural Connections
Interest Approach – Engagement
- In this lesson students will be using milk processing to learn about science and chemistry. First, help them understand exactly what milk is. Ask your students, "What is milk?" Accept most reasonable answers and use further questions to guide students to discover and recall from prior knowledge the following facts about milk:
- "Where does milk come from?" (Milk is produced by all mammals after they give birth. Although all mammals produce milk, cows produce it most efficiently to make it available for human consumption.)
- "What is milk made of?" (Milk is composed mostly of water [approximately 87%]. It also contains other solids such as fat, various proteins, carbohydrates [lactose], vitamins, and minerals.)
- In this lesson students will:
- Describe the history and benefits of milk processing; and
- identify the physical and chemical changes that transform milk into various dairy products.
Activity 1: History of Milk Processing
- Ask your students, What does the term 'food processing' mean? Allow students to use context clues and their background knowledge to define the term. Explain to students that many of the food products we eat must be processed in some way. Food processing takes place after food leaves the farm and before a consumer purchases it. Give examples such as pork being cured to make ham or bacon, apples being made into applesauce or apple juice, etc.
- Ask your students, What happens to milk after it leaves the dairy farm and before it is sold as milk, cheese, or yogurt in the grocery store?
- Use the infographic, The Milk Pasteurization Process provided by the National Dairy Council to explain the process of milk pasteurization. Project the image for your class to see and follow the pasteurization steps listed on the left side of the graphic.
- Once your students have learned the basic steps in milk pasteurization, ask them to use their prior knowledge by asking them the question, Do you think milk changes in any way when it is pasteurized?
- After students have thought about the question and provided possible answers, review the right side of the infographic. Compare the nutritional contents of milk before and after pasteurization. Pasteurization has proven effective in minimizing bacteria that causes illness. This process is accomplished without significantly altering the physical or chemical nature of milk.
- Transition to the next activity by pointing out that while pasteurization does not significantly change the physical or chemical nature of milk, other processes do and they can be for our benefit.
Help students draw a connection between science and our food supply (agriculture). Science plays a vital role in agriculture as our food is produced on the farm and processed (pasteurized) for our use.
Activity 2: Chemical and Physical Changes to make dairy products
- Write the words, "Chemical Change" on one side of your board and the words, "Physical Change" on the opposite side.
- Teach your students the difference between a chemical and physical change. Use the definition found in the vocabulary section of this lesson to define the difference between a physical and chemical change. List examples of each type of change to help students begin visualizing and understanding the principle.
- Examples of Physical Changes: Melting butter, water evaporating from a glass, molding clay into a new shape, etc.
- Examples of Chemical Changes: Rust forming on a nail, Baking a cookie, a piece of jewelry tarnishing, etc.
- Ask your students to brainstorm as many dairy products as they can think of. Make a list on the board. Although we drink fluid milk, the majority of milk produced is actually used to make dairy products such as yogurt, cheese, butter, ice cream, etc. How many dairy products can your students name?
- Using the graphic below, ask your students if it is a physical or chemical change that takes place when milk is made into various dairy products. To answer this question, your students must know a little more about how dairy products are made.
- Give each group 1 sheet of paper from the attached, Dairy Products-Chemical or Physical Change document. Each group will research the process of making a single dairy product. The students will learn how the dairy product is made and determine if it is a physical or chemical change that takes place.
- Provide internet access and allow students time to research their assigned dairy product and answer the 2 questions on their handout. Encourage them to include detailed answers.
- When the groups have completed their research and recorded their answers on the handout, have them place their handout on the board. If their dairy product required a chemical change, place the paper on the side of the board labeled "Chemical Change." If the dairy product required a physical change, place the paper on the side of the board labeled "Physical Change" (from step 1).
- Go through each dairy product as a class to teach the remainder of the students how each product is made and what type of change (chemical or physical) takes place to make it. You may lead the discussion or have each team present the facts for their dairy product to the class. As students present, check for accuracy and correct as needed.
Concept Elaboration and Evaluation
In summary, refer back to the Milk Products Graphic showing milk and 10 common dairy products milk can be made into. Ask students the following questions:
- "What happens to the value of milk as it is processed into these dairy products?"
- The value of milk increases. Milk processing increases the usefulness of milk as well as the demand, or need for milk.
- "How is chemistry used to develop these dairy products?"
- Chemistry and food science are interconnected. The process for developing each individual dairy product requires an extensive knowledge of the chemistry and components of milk.
- "What health benefits do we receive from processing milk into various dairy products?"
- Rather than simply drinking milk, we can obtain the nutritional benefits of milk with a variety of foods for many occasions. Milk processing is also a benefit to many individuals with lactose intolerance. They can often consume yogurt and cheese because the lactose has already been broken down.
We welcome your feedback! Please take a minute to tell us how to make this lesson better or to give us a few gold stars!
As students research their dairy product in Activity 2 (step 6), have them also find a short video clip to illustrate the process. If time permits, watch the video clips as a class to allow the students to actually see the process as it takes place in a milk processing plant. The "How It's Made" series produced by the Discovery Channel, SchoolTube, or YouTube are effective websites to search.
Though milk has been pasteurized and proven to significantly decrease the incidence of food-borne illness, some consumers would still like to consume raw, unpasteurized milk. Have students read the article found in the Essential Links, "Why is Milk Pasteurized? 4 Questions Answered." Challenge students to prepare a debate using scientific evidence to defend their stance.
Make cheese and butter in your classroom. Demonstrate a physical change by making butter. Use the instructions found in the Better Butter activity to allow students to see cream turn into butter. Demonstrate the chemical change that takes place to make cheese. Use the Biotech Cheese Kit or visit www.cheesemaking.com for more instructions.
Suggested Companion Resources
- Better Butter (Activity)
- Louis Pasteur and Pasteurization (Book)
- Biotech Cheese Kit (Kit)
- "Cheese Science-As Gouda as TV Gets" Video Series (Multimedia)
- Brittlelactica: Planet in Need (Multimedia)
- Consider the Source- Cheese (Multimedia)
- Dairy in the Mountain West: Our Family of Farmers (Multimedia)
- Food Chemistry Experiments (Teacher Reference)
- The American Dairy Industry (Website)
Agricultural Literacy Outcomes
Science, Technology, Engineering & Math
- Describe how agricultural practices have contributed to changes in societies and environments over time (T4.9-12.b)
Education Content Standards
Food Products and Processing Systems Career Pathway
FPP.02.01Apply principles of nutrition and biology to develop food products that provide a safe, wholesome and nutritious food supply for local and global food systems.
FPP.02.02Apply principles of microbiology and chemistry to develop food products to provide a safe, wholesome and nutritious food supply for local and global food systems.
Health Standard 7: Demonstrate the ability to practice health-enhancing behaviors and avoid or reduce health risks.
7.12.2Demonstrate a variety of healthy practices and behaviors that will maintain or improve the health of self and others.
Common Core Connections
Reading: Anchor Standards
CCSS.ELA-LITERACY.CCRA.R.1Read closely to determine what the text says explicitly and to make logical inferences from it; cite specific textual evidence when writing or speaking to support conclusions drawn from the text.
CCSS.ELA-LITERACY.CCRA.R.2Determine central ideas or themes of a text and analyze their development; summarize the key supporting details and ideas.
CCSS.ELA-LITERACY.CCRA.R.4Interpret words and phrases as they are used in a text, including determining technical, connotative, and figurative meanings, and analyze how specific word choices shape meaning or tone.
Speaking and Listening: Anchor Standards
CCSS.ELA-LITERACY.CCRA.SL.1Prepare for and participate effectively in a range of conversations and collaborations with diverse partners, building on others’ ideas and expressing their own clearly and persuasively.
CCSS.ELA-LITERACY.CCRA.SL.2Integrate and evaluate information presented in diverse media and formats, including visually, quantitatively, and orally.
CCSS.ELA-LITERACY.CCRA.SL.4Present information, findings, and supporting evidence such that listeners can follow the line of reasoning and the organization, development, and style are appropriate to task, purpose, and audience.
CCSS.ELA-LITERACY.CCRA.SL.5Make strategic use of digital media and visual displays of data to express information and enhance understanding of presentations.
Writing: Anchor Standards
CCSS.ELA-LITERACY.CCRA.W.1Write arguments to support claims in an analysis of substantive topics or texts using valid reasoning and relevant and sufficient evidence.
CCSS.ELA-LITERACY.CCRA.W.4Produce clear and coherent writing in which the development, organization, and style are appropriate to task, purpose, and audience.