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In this fact sheet: Rennet, Parmesan and other non-vegetarian cheese, Vegetarian Cheeses

Cheese is made by coagulating milk to produce curds (solids) and whey (liquid). The curds are separated from the whey so they can be processed and matured to produce a wide variety of cheeses. The coagulation of milk is achieved by the addition of rennet, the active ingredient of which is the enzyme chymosin (also known as rennin). Paneer, of Indian Origin, is one cheese which does not involve the use of rennet as heated milk is curdled with the addition of lemon juice or other acid food.

The traditional source of rennet is the stomach of slaughtered newly-born calves. Vegetarian cheeses are manufactured using rennet from either fungal/bacterial sources or genetically modified micro-organisms.


In cheese making, for milk to separate into curds and whey (curdling), the process requires the addition of rennet. Rennet contains the enzyme chymosin. Rennet can be sourced from the abomasum (fourth stomach) of newly-born calves where the chymosin aids digestion and absorption of milk. Adult cows do not have this enzyme. Chymosin is extracted from slaughtered calves by washing and drying the stomach lining, which is cut into small pieces and macerated in a solution of boric acid/brine for 4-5 days. Three of the major sources of protease for coagulating milk are from animal sources, veal calves, adult cows and pigs, the other three are from fungi.  

Parmesan and other non-vegetarian cheese

There are some cheeses which are always made using animal rennet, for example, Parmesan (Parmigiano Reggiano). In order to be called ‘Parmesan’ this has to be produced according to traditional methods which use calf rennet. The regulations for its production state the following ingredients; cows milk, salt and calf rennet. The milk comes from cows reared in the defined geographical area and the use of the term parmesan as a product description is limited by European Union labelling law to being region specific. Other cheeses which are always made using animal rennet include Grana Padano and Gorgonzola. You can get ‘Italian-style style hard cheese’, and variations of others which are suitable for vegetarians.

Vegetarian Cheeses

cheeseVegetarian cheeses are manufactured using rennet from either fungal/bacterial sources or genetically modified micro-organisms. The three main fungi used in the curdling process are Rhizomucor miehei, Endothia parasitica and Rhizomucor pusillis. In the 1960’s, United Nations Food and Agriculture Organisation (FAO) predicted that there would be a severe shortage of calf rennet due to the increased demand for meat resulting in more calves being reared to an older age and therefore less rennet being available. Addressing this issue, the last forty years have seen several substitutes for calf rennet being developed and today around ninety per cent of the hard cheese made in the UK is made using chymosin produced in genetically modified organisms (GMO’s) such as Escherichia coli, Kluyveromyces lactis and Aspergillus niger.





For example, chymosin can be made by the genetic modification of the yeast Kluyveromyces lactis. In this instance, the genetic material (DNA) encoding the protein chymosin is isolated from calf cells, which acts as a template. A copy of this DNA is inserted into yeast cells in a plasmid (small ring) which is then becomes copied within these. The yeast cells are cultivated and allowed to grow in a suitable environment, such as a fermenter vessel. The chymosin produced by the yeast cells is identical to the animal protein. The cheese itself is not made using a GMO but rather a product of this, i.e. the enzyme, which doesn’t remain in the finished product.
Vegetarian cheeses (and dairy-free cheeses suitable for a vegan diet) are widely available in supermarkets and health food stores, with a wide variety of cheeses now made with non-animal rennet and labelled as suitable for vegetarians.  There is no particular type of cheese which is exclusively vegetarian and soft cheeses are as likely to be non-vegetarian as hard cheese. 
Last updated March 2017

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The Vegetarian Society of the United Kingdom Limited, Parkdale, Dunham Road, Altrincham WA14 4QG
Registered Charity No. 259358, Registered Company No. 959115 (England and Wales)

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