Rennet is used in the production of cheese as a milk curdling enzyme.

It converts milk casein (protein) from a soluble to an insoluble material and during this process; the rennet separates the milk into solids (curds) and liquid (whey).

The different milk coagulation systems available is natural animal rennet rennet from GMO organisms, coagulating enzymes from plant origin and coagulating enzymes from non-GMO microbial origin.

Animal is the best, but a lot of people prefer not to use it, because of religious views.  The closest product is rennet from GMO origin, since chemically it is just like that of natural, animal origin, but here we also have a protesting fraction of people, because they believe this type of product will harm them in some way.  They thus do not perceive this as “natural”.

Plant coagulation enzymes are not used commercially, since they are very hard to standardize and usually have a lot of side reactions that can cause off-tastes and other problems in cheese.

Microbial rennet of non-GMO origin has vastly improved and now has very few side- reactions.  This rennet is used in large amounts in the world, since it is classified as Halal, Kosher and vegetarian.   Technically these are not rennet, but milk coagulating enzyme.  Different organisms are used to produce non-GMO microbial rennet.

Microbial rennet is a food grade enzyme system produced by the controlled fermentation for non-genetically modified Rhizomucor miehei . It contains the specific protease activity that makes it effective as a milk clotting enzyme. The rennet have been specially treated to make the enzyme thermal labile sensitive to inactivation by heat at pasteurization temperatures.  Rennet can be bought in tablets and as liquid or paste.

As the economical alternative to cloned/ calf rennet, microbial rennet liquid has the same uses, process conditions and clotting time.

When buying rennet, certain characteristics need to be taken into account. This will include activity of 1:50,000 MCU/ml, form which should be a dark brown liquid, solubility (miscible with water), odorless and a specific gravity of approximately 1.14g/ml.

Rennet requires the availability of calcium ions for activity. Calcium, added as calcium chloride should be in the range of 10 to 100 grams per 100 litres of milk for optimum performance. The effect of calcium chloride concentrates on the activity of various enzyme samples and is superior to animal rennet.

Enzyme use levels are generally dictated by processing conditions, milk composition and calcium chloride concentration. In a general a rate of one half  that of regular strength calf rennet can be used, but laboratory or pilot scale tests should be run to optimize dose levels.

Effective working temperature range plays a big role in performance. Calf rennet has a much narrower range of optimum working than most of the new “rennet” systems.

Due to it’s thermal labile nature, extra care should be taken when storing rennet; therefore it should be stored in sealed containers under refrigerated (4?C to 8?C) to minimize the loss of activity.

When using rennet to coagulate milk, always make sure to check the specification sheet of the product that you plan to use, to make sure that you are using it in the rifgt way to get the most out of that specific product.

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Rennet

Leon the Milkman

Dairy and Cheese Consultant

Cape Town, South Africa

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