Cheese-Making Enzyme Magic
1991 Woodrow Wilson Biology Institute
For any student level
This demo is a modification of an enzyme lab which is done as a "magic show". It's primary purpose is to tickle the curiosity of the student and grab interest before discussion of enzymes. It is also used to stimulate problem solving and to initiate questions as to how the "environment" influences activity even at the molecular level. It also uses materials which can be conveniently stored in a box from year to year and accessible with little advanced planning. This is not meant to be an experiment (see notes below).
- Powdered milk
- distilled H20
- 2-400 ml beakers
- 1-250 ml beaker
- stirring rod
- heat source (suggestion: use a hot plate with saucepan of water on top as a water bath)
- 1N HCl (keep in small dropper bottle for use year after year)
- milk digesting enzyme such as rennet or prepared liquid solution as ordered from Carolina Biological. I have found that the commercial preparation lasts for years under refrigeration and is therefore easily accessible.
- Before class, I turn on hot plate and get the water warm.
- As the students enter the room, I am using one of the 400 ml beakers to stir the powdered milk in water in quantities as directed on the package for one serving. The amounts are not critical and I find that extra powdered milk brings more dramatic results.
- Saying nothing, I pour the 250 ml beaker about 1/2 full of the milk. By now students have noticed and are asking questions. I tell them I am going to show them "something neat." I add 5 drops of the HCl (and with a flourish, an extra squirt). I place the beaker in the water bath and use the thermometer to determine when the temperature reaches 32� C. (This happens very quickly if you have the water already hot).
- After removing the milk from the water bath, I add about 1 ml of the milk digesting enzyme. I use a slight pause and add another squirt from the pipette as an afterthought. I leave the stirring rod in the beaker and now absent-mindedly "forget" it and go ahead with other topics. The beaker needs to sit at room temperature for 10-15 minutes--longer will not hurt as the milk will be coagulating.
- At some point before the end of the period, I suddenly remember the beaker, rush over and tug on the stirring rod. Students are amazed that it will stand upright by itself. Then I tip the beaker and nothing pours out. I act surprised and perplexed. Now the students are "hooked".
- I have the funnel lined with several layers of cheesecloth and standing in the other 400 ml beaker. I dump the mass into the funnel in one clump using the stirring rod to loosen it. Liquid begins to dribble down the funnel. At this point, I have the students come up for a closer look or walk around the class to show this stage. Then I pick up the cheesecloth and squeeze the moisture out over the funnel. When I open up the cheesecloth, I have the students guess what has happened. (It will look like cottage cheese and smell like "baby burps".)
Discussion and Analysis:
At this point I customize for any grade level. We discuss "cheese", curds and whey, Little Miss Muffet, and baby burps. We think about the word "cheesecloth" and they relate to something other than plastic cheese wrappers. We then discuss the enzyme activity and the factors which influence the rate of enzyme activity.
Depending on the grade level, I continue with spin-offs: milk digestion (especially in infants), food groups, temperature and pH and their influence on rates and activity, protein structure, acid indigestion, antacids, protein digestion in stomachs. A good home activity is to have the students design this into an experiment with controls, hypotheses, etc.
As time permits, I relate a story which gets student interest. All over the world, primitive peoples have used saclike stomachs of animals as portable canteens. At some point, the canteen may have been filled with milk. When lunch time rolled around, the herdsman may have discovered that the milk was lumpy with sharp or slightly sour taste. Cheesemaking had occurred and he had no idea that the enzymes released from the lining of the stomach were responsible. We then talk about other uses of enzymes as meat tenderizers, in breadmaking, etc.
Students should not eat this material as it contains lab acid.
Carolina Biological Supply Cheese/Enzyme Kit