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Jan. 22, 2010

Cheesy Chemistry

by Science Friday Education

Science Friday investigates the secret life of cheese. We visited Hendricks Farms and Dairy in Telford, PA--home to award-winning cheese-maker Trent Hendricks. He walks us through how he makes a hybrid cheese he calls cheddar blue.
 
Grade Level: 6th – 8th grade
Subject Matter: Chemistry
National Standards: NS.5-8.1, NS.5-8.2
 
Overview
There are hundreds of different kinds of cheeses that are produced in various countries around the world. Although each type of cheese has its own distinct taste, all cheese-making processes begin by separating the semi-solid portion of milk, called curd, from the watery liquid, known as whey.
In this activity, students will learn how to make a simple cheese using kitchen utensils and household ingredients. Students will discover the chemical reaction that occurs when an acid, vinegar, is mixed with a milk protein and how this chemical reaction separates the milk into curds and whey. Students also will use their five senses to observe and describe the physical properties of their cheese.
 
Activity Materials
Milk
Saucepan
Stove or hot plate
Oven mitts
Vinegar
Colander
Cheesecloth
String
Plastic cups
Salt and herbs (optional)
 
Vocabulary
Whey: liquid portion of milk containing water, sugar, minerals and proteins.
Curd: solid custard-like state of milk containing protein and fat.
Coagulation: the process of converting a liquid into a semi-solid mass.
Colloid: a suspension of small particles dispersed in another substance.
 
What To Do
  1. Start the lesson by having the students watch the video. Review cheese-maker Trent Hendricks’s description on how to make cheese with students. Tell students that they too will become cheese-makers for the day by making their own edible cheese. Before starting, make sure each student’s work area, cooking utensils and equipment are clean. Review the importance of following proper safety guidelines for handling kitchen equipment and utensils.
  2. Have students rinse out a saucepan with water to prevent the milk from sticking, and then pour one pint of milk into a saucepan. Slowly heat up the milk on the stove until it is just about to boil. At that point, students will see very small bubbles forming around the edge of the milk, where it meets the saucepan’s sides. Remove the saucepan from the heat.
  3. Slowly stir in one tablespoon of vinegar and continue to stir the milk. Ask students to describe what happens as they continue to stir. Tell students that the white stringy solids are the curds and the greenish liquid is the whey. Why is the milk separating into curds and whey? Based on the video, which part of the separated milk is used to make cheese?
  4. Have students line the colander with a cheesecloth and place it over a sink or bowl. Pour the contents of the saucepan onto the cheesecloth. What happens to the whey? Why do they think it is necessary to drain from the curd?
  5. Have students gather up the corners of the cheesecloth and tie the corners together with the string. Leave the curds for about one hour, so that they completely drain.
  6. After an hour has passed, have students scoop the curds into a plastic cup. Ask students to use their five senses to observe and describe the curds (texture, smell, taste, etc). Have students mix small portions of salt or herbs into the curds to add flavor (optional).
What's Happening?
Milk is a colloid mixture consisting mostly of water with small, suspended particles in it. These small particles are called milk solids. They consist of proteins, minerals, sugar, fat, and vitamins. In order to make cheese, the milk solids need to coagulate to form the curd. One method of inducing coagulation is to add an acid, such as vinegar, to milk. Vinegar contains hydrogen atoms with a positive charge. Since opposite charges attract, the positively charged hydrogen atoms in the vinegar are attracted to the negatively charged protein molecules. The attraction between these molecules causes them to clump together into a semi-solid mass, which is curd. Most of the milk solids remains with the curd while the rest is released in the whey.
 
Cheese-makers use alternative sources to coagulate milk including bacteria or an enzyme called rennet. (Rennet is what causes junket to thicken.) After making the curds, many cheeses are flavored by adding salt, herbs, mold or bacteria.
 
Topics for Science Class Discussion
  • What are the different production methods used by cheese-makers to separate milk into curds and whey?
  • What are the different factors used to produce a wide variety of cheeses with different flavors and textures?
  • Will cheeses made from different types of milk (cow, goat, soy, sheep, camel, among others) have the same texture or taste?
  • When and how did people first make cheese?
Extended Activities and Links
  • Experiment with variations in your cheese recipe by using different types of milks and seasonings, or by substituting the vinegar with lemon juice. Have students create a chart that compares and contrasts smell, taste and texture for each modified recipe.
  • Have each student research the history and production method for a specific type of cheese. Have a “Say Cheese Day” where students present their findings and sample each variety of cheese.
  • Wisconsin is one of the leading producers of cheese. Learn about their cheese-making history and production methods. Kid-friendly cheese recipes are also available online.
  • Download free educational information and activities on cheese and other diary products.

 

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