What Is Coagulation? Coagulation is the process that transforms liquid milk into solid curd. This solid curd is also called 'gel' (from the milk). Coagulation can occur in three different ways: 1. Enzyme Action 2. Acid Addition 3. Acid/Heat Addition
Rennet
What Is Rennet? Rennet is the coagulant used in the cheese making process. Rennet is the name of an enzyme that causes the proteins in milk to link together, thus creating a solid mass called 'milk curd.' There are three different types of rennet. 1. Traditional Rennet - this rennet comes from the stomach of an animal. 2. Bacterial Rennet - this rennet is also sometimes called 'vegetable rennet'. It comes from recombinant (recombining, to combine again or differently) bacteria using DNA from from veal (the flesh of a calf) calf stomach cells. 3. Microbial Rennet - this rennet comes from a fungus.
How And When Was Rennet Discovered? Rennet was discovered along with cheese in around 8000 BC. Rennet was discovered in the stomachs of some ruminants (cattle, sheep, antelopes, deer, giraffes, etc.). The leak proof stomachs of these animals helped transport milk and other liquids through the body of the animal. Without the refrigeration of the animals, the warm summer heat and the remaining rennet in the stomach lining of the animal would have combined and produced the earliest and most natural form of cheese (or curd) in the animal's stomach. These milk curds were strained and given salt, making a new form of 'cheese.' The freshness of this cheese, even given the added salt, meant that this cheese was to be eaten and produced daily if it were to not spoil.
Plant Rennet Plant rennet is a type of rennet derived especially from plants - cardoon thistle, artichoke, nettles, and others. Plant rennet can be difficult to work with for a number of reasons, one of which being about how the strength of plant rennet is non-consistent. Because of this non-consistency, knowing how much to add to milk to get it to coagulate can be difficult. The second reason is how plant rennet can change the flavor of cheese - which can be either a positive or negative thing. For example, thistle rennet is used to produce a number of different cheeses, but it can also give the cheese a vegetal or bitter flavor, which is why it is avoided by most cheese-makers.
Rennet Temperatures The temperature at which rennet sets milk is between 85 degrees Fahrenheit and 105 degrees Fahrenheit. However, the rennet will continue setting the milk if it is within the correct temperatures, so it is best if the curds are cut in a very timely manner. If the curd is not cut quickly, the curd will become to hard for the cheese.
Junket Rennet
What Is Junket? Junket is a weak form of rennet. It is traditionally used to set custards and other soft cheeses because it is incapable of producing curd hard enough for quality cheese-making. It is definitely possible to set milk with junket; however, it will only produce a very soft milk curd.