A substance called rennet was harvested from frozen calf stomachs, and then an enzyme calledrennin was purified from the rennet. Nursing calves need rennin to digest milk. Purified rennin is necessary to produce firm cheeses.
The digestive system of the cow: http://www.teachersdomain.org/asset/nat08_vid_digest/
Rennin reacts with the milk protein casein and causes it to clump together or form curds. Formation of these curds is the first step in producing hard cheeses. However, because it was difficult to isolate enough rennin from calves to meet the large global demand for cheese, scientists worked to produce the enzyme using biotechnology. The rennin gene was isolated from calves' stomachs, cloned into a plasmid, and transformed into E. coli. The bacteria were then used to produce the recombinant enzyme chymosin.
To produce large quantities of chymosin, which can then be isolated and purified for commercial cheese production, bacteria are grown in bioreactors. A large part of global cheese production is conducted using recombinant chymosin.
Download the free app Molecules on your iPad and search for the enzyme Bovine Chymosin
Watch this you tube view on basic ideas of enzyme activity.
In this video high school teacher Diane Provenzano leads her biotechnology class through a discussion of the results of a lab activity in which they tried to produce cheese curds using two different enzymes: a nonrecombinant enzyme (rennin) and a recombinant enzyme (chymosin).
Now you will become cheese-makers for the day by making your own edible cheese!
Before you begin, watch the video called Cheese: Not the Same Mold Story
1 gallon milk (see notes below)
1/4 rennet, tablet or 1/4 teaspoon liquid rennet
1/4 cup cool un-chlorinated water (most bottled water is un-chlorinated)
2 teaspoons citric acid
1 teaspoon salt
• Animal Rennet:
New England Cheesmaking Supply Company 413-628-3808: www.cheesemaking.com
• Citric Acid order from Amazon.com
To begin: 30 Minute Mozzarella
The Milk: Make sure the milk you use for this cheese is NOT ULTRA- PASTEURIZED--Homogenized milk will work fine. --Fresh farm milk will also work well but we encourage you to try with 1 gallon of store bought whole milk first.--Low fat milk will work but the cheese will be drier and less flavorful.
You will need:--A 6 to 8 quart stainless steel pot. Aluminum or cast iron will not work.--A stainless steel or strong plastic slotted spoon.--A two quart microwave safe mixing bowl--measuring spoons--A thermometer which will clearly read between 80 - 120 degrees F.
Prepare your work area: Do not prepare any other food while you are making cheese. Put all food products away. Move all sponges, cloths and dirty towels away from your work surface, wipe your sink and stove with soap and water. Finally use your antibacterial cleaner to wipe down all surfaces.
Process: Crush 1/4 tablet of rennet and dissolve in 1/4 cup of cool un-chlorinated water and set aside to use later.
Heat the milk to 90F and add 1.5-2 teaspoons of citric acid. This will bring the milk to the proper acidity to stretch well later.
As you approach 90F you will notice your milk beginning to curdle due to acidity and temperature.
When at 90F add your rennet (which you prepared in previous step) to the milk and stir in a top to bottom motion for 30-60 seconds -- then stop.
Now turn the heat off (it may continue to rise as high as 105F or so).
Let the milk remain quiet for the next 3-5 minutes during which it will form a curd. A longer set will result in a firmer curd.
Cut the curds into a 1" checkerboard pattern and then scoop with a slotted sp0on into a heat proof bowl to be used in the microwave. (If the curd is too soft at this point let sit for another minute or so).
You will now press this curd gently with your hand, pouring off as much whey as possible. Reserve this whey to use in cooking or making ricotta.
Microwave the curd on HI for 1 minute. You will notice more whey has run out of the curd. Drain off all whey as you did before.
Quickly work the cheese with a spoon or your hands until it is cool enough to touch (rubber gloves will help since the cheese is almost too hot to touch at this point).
Microwave 2 more times for 35 seconds each and repeat the kneading as in the last step. Drain all of the whey off as you go.
Knead quickly now as you would bread dough until it is smooth and shiny. Add salt near the finish.
At this point the cheese should be soft and pliable enough to stretch like taffy.
It is ready to eat when it cools.
Form it into a ball and drop into ice water to cool and refrigerate.
When cold you can wrap in plastic wrap and it will last for several days but is best when eaten fresh.
Now that you have made your cheese: watch this video and learn about cheese making history and production methods:
Topics for 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?
- Experiment with variations in your cheese recipe by using different types of milks and seasonings, or by substituting ingredients. 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.