Production and Action of Rennet
One of the first steps in the manufacture of most varieties of cheese is the use of milk coagulating enzymes to form a curd. The discovery and use of rennet predates recorded history.
The stomachs of many animals possess the power of coagulating milk. It was discovered in time that the stomachs of calves were the best for this purpose.
RENCO calf rennet liquid is a saline solution of milk coagulating enzymes extracted from the fourth stomach of the bovine calf. The active components of the preparation are the enzymes chymosin and pepsin.
RENCO NEW ZEALAND
Renco New Zealand is the only commercial manufacturer of rennet in New Zealand. It was established in 1916 (as The New Zealand Rennet Company) to assure the dairy industry of a supply of rennet, which was almost unprocurable during the First World War. The formation of the Company resulted in the establishment of the bobby calf industry in New Zealand.
Rennet manufactured by the Company is found around the world, where it enjoys the reputation of being of high purity and exceptional quality, reflecting the quality of the New Zealand raw materials and the manufacturing process.
Renco New Zealand processes most of New Zealands crop of calf stomachs (actually the fourth stomach or abomasum, commonly called a vell), amounting to about 1,000,000 pieces annually.
Rennet consists of two active components, chymosin (sometimes referred to as rennin) and pepsin. These two components are the enzymes which are secreted into the stomach of the animals. In the new-born calf chymosin predominates in the secretions (95% chymosin / 5% pepsin). As the animal ages, or its diet changes front milk to grass, these secretions change and at about nine months of age the secretions have reversed (10% chymosin / 90% pepsin).
Of the two enzymes, chymosin is the preferred enzyme for cheesemaking as it is more specific in its action on the milk proteins, although pure pepsin can be utilised to manufacture cheese. NZ operates a very effective calf collection system. Consequently New Zealand rennet extract has a high chymosin content and this has contributed to its high reputation world wide.
RENNET ACTION / CHEESE-MAKING
In making cheese we are attempting to preserve the milk by :
In simple terms milk consists of a mixture of colloidal proteins (caseins), soluble whey proteins, fat (as an emulsion), lactose and minerals. The casein component is present in the milk as a suspension of very small particles called micelles.
Rennet action is primarily involved in precipitating the casein component of milk. This is an enzymatic process and results in a soft, smooth curd (or gel). The gel has the property of being elastic and shrinkable.
In forming the curd the large fat globules are trapped within the casein gel and are recovered with the curd. The casein gel, assisted by acid produced by starter organisms and the application of mild heat, is able to shrink. This concentrates the casein and fat components with the expulsion of whey, and reduces the moisture content of the curd. This shrinkage of the casein gel is called syneresis.
Control of the final moisture in cheese curd is controlled by:
HANDLING OF RENNET
Rennet is an enzyme preparation, an enzyme is a protein. Being a complex organic substance it is very susceptible to the way it in stored and handled (see graph).
Rennet should be stored refrigerated (4ºC) away from direct sunlight to preserve maximum activity (Ultra-violet rays in sunlight destroy the rennet activity).
Where rennet is being diluted prior to use this should be done with clean cold, chlorine free water. Chlorine is a strong oxidizing agent and rapidly destroys the enzymes.
FACTORS affecting COAGULATION
Coagulation of milk is affected by a number of factors:
CONCENTRATION of rennet - increasing the amount of rennet reduces the coagulation time.
TEMPERATURE of milk - increasing the temperature of the milk reduces the coagulation time. However, rennet is inactivated above temperatures of about 40ºC (see graph).
ACIDITY/pH - the lower the pH of the milk at the time of renneting the faster the coagulation time.
MILK COMPOSITION - eg calcium content or casein levels. Towards the end of the season calcium levels in the milk tend to decline resulting in poor coagulation. In such cases the addition of calcium chloride to the milk improves the set.
MILK QUALITY - poor quality milk with high bug counts may result in poor sets due to microbial attack on the proteins.
HEAT TREATMENT - excessive heat treatment results in a weak curd structure (UHT milk may not gel at all when treated with rennet). Normal pasteurization does not significantly affect the coagulation properties of milk.
There is a world wide shortage of raw materials for the manufacture of calf rennet.
Calf rennet, or more specifically chymosin, is the standard coagulant against which all other alternative coagulants are measured.
All the alternative rennets are proteolytic enzymes (proteases); all have lesser specificity in their action than chymosin.
CALF RENNET - as previously discussed
BOVINE RENNET - rennet extracted from adult bovine animals contains about 10% chymosin and 90% pepsin. For a given activity, twice as much is required in the vat to achieve the same result.
PIG PEPSIN - this rennet is not particularly satisfactory by itself
LAMB RENNET - limited commercial acceptance.
Protease's produced by micro-organisms such as Mucor miehi and Endothea parasitica.
FERMENTATION PRODUCED CHYMOSIN
Using genetic engineering to insert the gene for chymosin production into a microorganism. A chymosin product can be produced by fermentation processes, having all the desirable attributes of calf chymosin.
For more details on RENCO Natural Calf Rennet products please contact us.
Specification sheets for all of our products are available on request.