Easy Enzyme Experiment: Rennet and Cheese Making

Curds separating from whey after being mixed with rennet.

Learning about cheese can be an amazingly diverse education in history, culture, as well as science.  Cheese making beautifully integrates both art and science, one without the other will result in a mediocre cheese at best.  Of course milk of all types is the primary ingredient in making cheese.  Along with milk though many combinations of bacteria, enzymes, aging processes, moisture, humidity, and other factors are controlled in the cheese making process.  Most cheeses found in the supermarket utilize a specific enzyme (or rather a complex of enzymes) called rennet.  Typically, rennet is one of the first things added to milk in the cheese making process.  Once added, it immediately starts separating curds and whey.  Rennet acts on the milk protein casein by making it non-soluble.  Milk is normally white because casein protein is dissolved and floating around in it.  However, when casein is made insoluble through the action of acids or enzymes like rennet, it precipitates out forming white clumps called curds.  For a few of the most basic cheeses only rennet is utilized.  Most cheeses found in the supermarket however utilize a combination of bacteria and rennet.  For this cheese making experiment we will only use rennet in order to display its function.

As with the history of yogurt, the history of rennet goes back many thousands of years.  And similar to how most great discoveries are made, rennet was likely discovered by accident.  Presumably, we can imagine, thousands of years ago some dairy worker ran out of milk containers.  The dairy worker also had probably just butchered a young animal and found a left over stomach.  Thinking the stomach would make a good milk container, filled it up and let it sit.  When the worker came back at a later time he would have been surprised to find the milk was now separated into curds and whey but not rotten smelling.  Then by draining off the whey the curds would have made the first cheese.  This would have been the first known accidental use of rennet.  

Being rennet begins the process of digesting milk it makes perfect sense that it would be found in the stomach of a young animal from the dairy herd.  This is in-fact where most rennet historically has come from.  Today however, rennet is often created by bacteria in a laboratory or derived from plant based products.  Various plants, for example stinging nettle, have enzymes in them that have effects on milk similar to rennet.  From what I have heard, animal based rennet works best.  But each cheese maker has their preferred and even secret type of rennet, and boy can they be opinionated!  I personally have used Junket rennet tablets with what I consider good results.  Junket and other rennets can be found and purchased on Amazon and occasionally in the supermarket.

How to make rennet cheese:

Materials: Spoon, stainless steel pot, thermometer, and strainer

Ingredients: Milk, water, salt and rennet

1. Heat the milk to 180 degrees Fahrenheit.  This pasteurizes the milk so no bacteria cause it to spoil.  Slowly heat milk and stir gently every once in a while to ensure milk does not burn.

2.  Depending on the directions on the type of rennet you purchase, mix up the rennet.  For Junket dissolve your tablet in ¼ cup of cool water.  I prefer to mix ½ tablet with ¼ cup water.

3. Let milk cool to about 100 degrees Fahrenheit.  Add the rennet solution and mix by st iring for about 1 minute.  

4. Let milk/rennet mixture sit as close to 100 degrees as possible overnight.  Let the mixture sit absolutely still, do not disturb!

5. The next day the curds should be separating from the whey.  Simply dump these through a strainer to separate.  The curds left in the strainer is the cheese.  Transfer the curds to another container and salt to taste.

Curds after straining and salting.

The body temperature of a cow is about 100 degrees, so it makes sense that rennet would work best at this temperature.  At cooler temperatures rennet either will not work or will work very slowly.  Warmer temperatures will break down, or denature, the enzyme so it won’t work at all.  

After the curds and whey are separated the resulting cheese will be very soft and will taste like milk.  Unfortunately, at least for this cheese, most taste is derived through bacterial metabolism.  What this basic rennet cheese is known for though is adding things into it.  It is often used as a cheese for making spicy dips also when mixed with chili peppers.  Other fruits, veggies, and herbs can also be mixed with it and it can be used as a cream cheese. You can experiment and come up with your own recipe.