Coagulation of milk

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To find out the optimum concentration of calcium chloride (CaCl2) needed to be used by cheese manufacturing companies, in order for the milk used to produce the greatest mass of cheese from a given amount of milk to coagulate at its best rate. So that the rennet is at its most active effect therefore achieving a more solid coagulation at the maximum time of production.


Increasing the calcium chloride concentration will increase the mass of curd produced, this is upto an optimum concentration.


I predict that the rate at which the milk coagulates thus mass of curd produced will increase as the concentration of calcium chloride increases. This rule will apply upto the stage where an increase in calcium chloride causes no further increase in mass of curd produced as the calcium chloride is allowing the enzyme to have its optimum activity.

Background information:

When making cheese large quantities of milk are required. Cheese is made by coagulating milk to give curds, which are then separated from the liquid, which is called Whey. The curd is then processed and matured to produce cheese.

To coagulate milk you use the addition of rennet, which is made from the lining of a calf’s stomach. Rennet contains a specific enzyme called chymosin also known as rennin. 90% of rennet is chymosin and the 10% is pepsin. The enzyme chymosin causes the particles of milk protein to join together to form a solid gel, which contains liquid called whey. The liquid whey is then drained out of the gel leaving the solid, which is called curd left behind. The pieces of curd are then pressed together forming cheese, and are then stored in rooms of controlled temperatures where the enzymes present act on the protein and fat giving cheese its distinctive cheesy taste.

The history of milk coagulants comes from accident times in Eastern Europe and western Africa. In those days people carried milk in bags, which were made of animal’s stomachs. The formation of cheese occurred literally by accident. By carrying milk in these bags made out of animal’s stomachs it resulted in the first formation of cheese.

The rennet is usually sourced from the fourth stomach of newly born calves, called abomasum. The reason being for chymosin to be present in the abomasum it that it is used to digest and absorb milk.

Chymosin breaks down milk protein casein into paracasein. This binds with calcium to form calcium paracaseinate. This helps separates out with milk fat and some water which forms a mass called curd.

Enzymes are globular proteins. They are specific and only catalyse one chemical reaction. Enzymes are catalysts because they are neither used up nor changed in any way by the reactions they catalyse. The folding of an amino acid chain forms an enzyme. When the chain is folded hydrogen bonds and disulphide bridges are formed which give the protein a stable structure.

Enzymes are specific this is because they have a particular tertiary structure. Their tertiary structure gives rise to an active site, a depression in the globular protein with a shape that is complementary to the shape of the substrate. The substrate will bind to the active site forming an enzyme substrate complex. There will be a reaction here for a brief period, after the products will be released from the active site and a new reaction will take place as the enzyme will bind to another substrate forming an enzyme substrate complex again. This is until the enzyme becomes exhausted.

The addition of calcium chloride to milk was introduced some decades ago when coagulants contained a high percentage of pepsin. This enzyme was very dependent on the calcium ion for having a good coagulant activity. Now coagulants used contain no pepsin and are much less dependent on calcium for good coagulation.

However, the addition of calcium chloride can help to reduce the amount of coagulant needed to achieve a proper set. While the addition of CaCl2 is legally allowed up to 6 oz per 1000 lb of milk, its overuse can result in short-bodied cheese.


The term ‘variable’ means liable or capable to change. Variables are parameters that can be altered or measured in the experiment.

In an investigation there are many variables such as independent, dependent and confounding variables, which are discussed below. By being able to acknowledge which variables are which we are able to manipulate information of what is being investigated. We are also able to investigate certain variables this is done simply by controlling all the variables in the investigation apart for the one being tested. This helps makes sure you are testing the variable you wish to and no other.

The independent variables are what we are studying the effects of, the variable that is manipulated or changed and the thing that is the cause of the results. In this experiment the independent variable is the concentration of calcium chloride.

The dependant variables are what we measure in the investigation. The results on the dependant variable are dependant on how the independent variable has been manipulated. The dependant variable in this investigation is the mass of curd produced.

The other variables which can effect the results are called confounding variables and will be controlled in order for the results to be reliable. Below is a list of the factors, which can effect the investigation.

Temperature at which the experiment will be carried out has to be maintained and kept constant this is to enable a fair test. The temperature will be maintained at 30oc by using a thermostatically controlled water bath. If the temperature was to be increased from 30oc which is the temperature being used in the experiment the activity of the solutions will increase causing the rate at which the milk will coagulate to increase, and visa versa if the temperature was to be decreased the rate at which the milk would coagulate would also decrease.

Concentration of rennin has to be kept constant. If the concentration is altered the results collected will not just measure the effect of calcium chloride but also the effect of rennin concentration on the coagulation of milk. By increasing the concentration of rennin the milk will coagulate more quickly. I say this because there will be more active sites available from the enzyme which will bind to more substrates therefore forming more enzyme substrate complexes thus the rate at which the milk will coagulate will increase or visa versa if the rennin concentration was to decrease the rate at which the milk would coagulate would not be as effective as if the concentration was to be greater. This is because the number of active sites would decrease therefore the enzyme would become saturated quickly. For the same reason above the volume of rennin used in the experiment will also be kept constant.

The time the solutions CaCl2, rennet and milk will be left to react will be kept constant at 420 seconds (7minutes), this is so that they are all investigated under the same conditions. If the solutions were left to react for times that differed the mass of curd produced would be different. This is because some of the solutions would react more than others therefore producing more curd.

Only one type of milk will be used in this investigation. This is because for example goat’s milk in comparison to cow’s milk will coagulate at a different rate. Therefore by using different types of milk the rate at which the milk coagulates will be different which will cause the results to change according to which type of milk is being used. This is why only full fat cows milk is to be used in this investigation. The volume of milk used in the experiment will also be kept constant this is to initiate a fair test.

The time the solutions rennin, calcium chloride and milk, which will all be mixed, is to be filtered will also be kept at a constant of 900 seconds (15minutes). This is to allow a time long enough for the curd and solution to filter and also an equal and constant time for the solutions to react and produce curd which will help initiate a fair test when the experiment is repeated.

The time of incubation in the water bath will also be kept constant. I will incubate the boiling tubes containing the three solutions separately for 420 seconds (7minutes) prior to mixing the contents all together this is to make sure all the solutions were at a constant temperature of 30oc before mixing. This will keep a fair test.

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