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CHEESES.TXT
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1995-03-13
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VegSocUK Information Sheet
THE VEGETARIAN SOCIETY
CHEESE & RENNET
___________________________________
Cheese is made by coagulating milk to give curds
which are then separated from the liquid, whey, after which they can be
processed and matured to produce a wide variety of cheeses. Milk is
coagulated by the addition of rennet. The active ingredient of rennet is the
enzyme, chymosin (also known as rennin). The usual source of rennet is the
stomach of slaughtered newly-born calves. Vegetarian cheeses are manufactured
using rennet from either fungal or bacterial sources. Advances in genetic
engineering processes means they may now also be made using chymosin produced
by genetically altered microorganisms.
MANUFACTURE
The exact processes in the making of cheese varies between different
varieties. However, all cheeses are made by essentially the same method.
Initially, the milk is usually pasteurised by heating at 720C for 15 seconds
to destroy potentially harmful bacteria. The milk is then cooled to around
300C and a starter culture of lactic acid bacteria is added to help souring.
These convert lactose into lactic acid and help in the coagulation process.
In addition, they also have a beneficial effect on the eventual quality,
taste and consistency of the cheese. Some cheeses are coagulated entirely by
lactic acid bacteria and are known as lactic- curd or acid-curd cheeses.
However, some cheeses sold as lactic-curd cheese may have had rennet added.
The next stage is the addition of rennet, containing the enzyme chymosin.
Rennet is usually sourced from the abomasum (fourth stomach) of newly-born
calves. Here, chymosin aids the digestion and absorption of milk. Adult cows
do not have this enzyme. Chymosin is extracted by washing and drying the
stomach lining, which is then cut into small pieces and macerated in a
solution of boric acid or brine at 300C for 4-5 days. Pepsin may sometimes be
used instead of chymosin. This is usually derived from the abomasum of grown
calves or heifers, or less commonly pigs. Pepsin may be mixed with calf
rennin. Rennet coagulates the milk, separating it into curds and whey. This
is called curdling. Chymosin breaks down the milk protein casein to
paracasein which combines with calcium to form calcium paracaseinate, which
separates out. Milk fat and some water also becomes incorporated into this
mass, forming curds. The remaining liquid is the whey. The strength of
different rennets can vary, though usual strength varies between 1 : 10 000
and 1 : 15 000 ie one part rennin can coagulate 10 - 15 000 parts milk.
Other substances may also be added during the cheese making process.
Calcium chloride is added to improve the curdling process, and potassium
nitrate is added to inhibit contaminating bacteria. Dyes (eg annatto,
beta-carotene), Penicillium roquefortii mould spores to promote blue veining,
or propionic acid bacteria to encourage hole formation may be added.
Following curdling, the curds are cut and drained. The size of the cut and
the methods used vary for different cheese varieties. For soft cheeses, the
curds are sparingly cut and allowed to drain naturally. For hard cheeses, the
curds are heated and more whey is drained off. The curds are then cut into
small pieces, placed in vats and pressed.
After pressing, the curds may be treated in a number of ways. They may be
moulded into different shapes, soaked in a saltwater solution, be sprayed
with mould forming spores or bacteria, washed in alcohol, or covered in
herbs.
The final stage is ripening, or maturation. This can vary in length from 4
weeks to 2 - 3 years, depending on the type of cheese. During ripening
flavours develop, the cheese becomes firmer and drier, and special
characteristics such as holes, blue veining and crust formation occurs.
VEGETARIAN CHEESES
Vegetarian cheeses are made with rennets of non-animal origin. In the past,
fig leaves, melon, wild thistle and safflower have all supplied plant rennets
for cheese making. However, most widely available vegetarian cheeses are made
using rennet produced by fermentation of the fungus Mucor miehei. Vegetarian
cheese may also be made using a rennet from the bacteria Bacillus subtilis or
Bacillus prodigiosum.
Advances in genetic engineering techniques mean that some vegetarian cheeses
may now be made using chymosin produced by genetically engineered
microorganisms. The genetic material (DNA) which encodes for chymosin is
introduced into a microorganism which can then be cultured to produce
commercial quantities of chymosin. This is done by extracting genetic
material from calf stomach cells which acts as a template for producing the
chymosin encoding DNA. This can then be introduced into the microorganism.
Once the genetic material is introduced there is no further need for calf
cells. Alternatively, the chymosin encoding DNA can be biosynthesised in the
laboratory without the use of calf cells.
The chymosin produced is identical to that produced by calf stomach cells.
The development of genetically engineered chymosin has been encouraged by
shortages and fluctuations in cost of rennet from calves. It's manufacturers
claim that genetically engineered chymosin will end the cheese making
industry's reliance on the slaughter of calves.
Chymosin encoding DNA has been introduced into three different
microorganisms. These are the yeast Kluyveromyces lactis, the fungus
Aspergillus niger var awamori, and a strain of the bacteria Escherichia coli.
All of these have now been approved and cleared for use by the Ministry of
Agriculture, Fisheries & Food. There is no legal requirement for
manufacturers to state whether a genetically engineered rennet has been used
in the cheese making process.
Vegetarian cheeses are widely available in supermarkets and health food
stores. A wide variety of cheeses are now made with non- animal rennet and
labelled as suitable for vegetarians. No particular type of cheese is
exclusively vegetarian. Soft cheeses are as likely to be non-vegetarian as
hard cheeses. A list of cheeses suitable for vegetarians is available from
The Vegetarian Society.
TYPES OF CHEESE
The type of cheese produced depends on the milk used and the cheese making
process. The milk used may be full fat, semi- skimmed or fully skimmed, this
affecting the fat content of the cheese. It may be pasteurised or
unpasteurised. Milk from different animals and different breeds is important
in determining the final flavour. As well as cow's milk, cheese may be made
from sheep or goat's milk.
Soft cheeses may be fresh or ripened. Fresh cheeses include quark, cottage
cheese and cream cheese. Ripened soft cheeses include Brie and Camembert.
Semi-soft cheeses include Stilton, Wensleydale and Gorgonzola. Hard cheeses
include Cheddar, Cheshire, and Gruyere. Parmesan is a strongly pressed, very
hard, dry cheese ripened for 2 - 3 years and then grated. Whey cheeses such
as Ricotta are made as a by-product of other cheeses from the whey removed
during pressing. Processed cheeses are either made with trimmings that are
left over from the manufacture of other cheeses, or from dried milk powder.
Flavourings, colourings and other additives are used.
NUTRITIONAL ASPECTS
Cheese is a good source of protein, calcium, zinc, and vitamin B12. However,
full fat cheese is a major source of saturated fat which can lead to raised
serum cholesterol levels. Also, it contains no carbohydrate or fibre, and is
a very poor source of iron. Vegetarians, particularly new vegetarians, should
be wary of too high a consumption of cheese.
___________________________________
//
This article is copyright to the Vegetarian Society (UK), but may be freely
copied for non-commercial use provided it is kept intact, not altered
and these lines are included.
For futher information contact: The Vegetarian Society, Parkdale, Dunham Road,
Altrincham, Cheshire WA14 4QG, England. Tel: (England) 061 928 0793
email: vegsoc@vegsoc.demon.co.uk
//
[The text of this file was obtained from the Vegetarian Society (UK) in
March 1995.]