Rennet
From Wikipedia, the free encyclopedia
Rennet /ˈrɛnɨt/ is a
complex of enzymes
produced in any mammalian stomach, and is often used in the production of cheese. Rennet contains many enzymes,
including a proteolytic enzyme (protease)
that coagulates the milk, causing it to separate into solids (curds) and liquid (whey). They are also very important in
the stomach of young mammals as they digest their mothers' milk. The active enzyme in rennet is called chymosin
or rennin (EC 3.4.23.4)
but there are also other important enzymes in it, e.g., pepsin and lipase. There are non-animal sources for
rennet that are suitable for consumption by vegetarians.
Production
of natural calf rennet
Natural calf rennet is extracted from the inner mucosa of the fourth stomach chamber (the abomasum)
of slaughtered young, unweaned calves. These stomachs are a by-product
of veal
production. If rennet is extracted from older calves (grass-fed or grain-fed) the rennet contains less or no
chymosin
but a high level of pepsin and can only be used for special types of milk and cheeses. As each ruminant
produces a special kind of rennet to digest the milk of its own species,
there are milk-specific rennets available, such as kid goat rennet for goat's milk and lamb
rennet for sheep's
milk.
Traditional
method
Dried and cleaned stomachs
of young calves are sliced into small pieces and then put into saltwater or whey, together with some vinegar
or wine
to lower the pH
of the solution. After some time (overnight or several days), the solution is
filtered. The crude rennet that remains in the filtered solution can then be
used to coagulate milk. About 1 gram of this solution can normally
coagulate 2 to 4 litres of milk.
This method is still used by some
traditional cheese-makers in Austria,
France,
Greece,
Italy,
Romania,
Switzerland,
Sweden,
and the United Kingdom (among others).
Modern
method
Deep-frozen stomachs
are milled and put into an enzyme-extracting solution. The crude rennet extract
is then activated by adding acid; the enzymes in the stomach are produced in an inactive form
and are activated by the stomach acid.
The acid is then neutralized and the rennet extract is filtered in several stages and
concentrated until reaching a typical potency of about 1:15,000; meaning
1 gram of extract can coagulate 15 kg (15 litres) of milk.
In 1 kg of rennet extract,
there are about 0.7 grams of active enzymes – the rest is water and salt and
sometimes sodium benzoate, E211, 0.5% - 1% for preservation. Typically, 1 kg of cheese
contains about 0.0003 grams of rennet enzymes.
Alternative
sources of rennet
Because of the limited availability
of mammalian stomachs for rennet production, cheese makers have looked for
other ways to coagulate the milk since at least Roman
times. There are many sources of enzymes, ranging from plants, fungi, and
microbial sources, that can substitute for animal rennet. Cheeses produced from
any of these varieties of rennet are suitable for lacto-vegetarians to consume. Fermentation produced chymosin (FPC)(see below)
is used more often in industrial cheesemaking in North America and Europe today
because it is less expensive and of higher quality than animal rennet.[1]
Vegetable
rennet
Many plants have coagulating
properties. Homer
suggests in the Iliad and the Odyssey
that the Greeks used an extract of fig juice to coagulate milk.[2]
Other examples include dried caper leaves,[3]
nettles,
thistles,
mallow,
and Ground Ivy (Creeping Charlie). Enzymes from thistle or cynara
are used in some traditional cheese production in the Mediterranean.
Phytic acid, derived from unfermented soybeans, or Fermentation-Produced Chymosin
(FPC) may also be used.
Vegetable rennets are also suitable
for vegetarians.
Vegetable
rennet might be used in the production of kosher
and halal
cheeses but nearly all kosher cheeses are produced with either microbial rennet
or FPC.[citation needed] Worldwide, there is no industrial production for vegetable
rennet. Commercial so-called vegetable rennets usually contain rennet from the mold Mucor miehei - see microbial
rennet below.
Microbial
rennet
Some molds such as Rhizomucor miehei are able to produce proteolytic enzymes. These molds are
produced in a fermenter and then specially concentrated and purified to avoid
contamination with unpleasant byproducts of the mold growth. At the present
state of scientific research, governmental food safety organizations such as
the European Food Safety Authority
deny QPS (Qualified Presumption of Safety) status to enzymes produced
especially by these molds.
The flavor and taste of cheeses
produced with microbial rennets tend towards some bitterness, especially after
longer maturation periods.[4]
Cheeses produced this way are suitable for vegetarians,
provided no animal-based alimentation was used during the production.
Fermentation-produced
chymosin (FPC)
Because of the above imperfections
of microbial and animal rennets, many producers sought further replacements of
rennet. With the development of genetic engineering, it became possible to
extract rennet-producing genes from animal stomach and insert them into certain
bacteria,
fungi
or yeasts
to make them produce chymosin during fermentation. The genetically modified microorganism
is killed after fermentation and chymosin isolated from the fermentation broth,
so that the fermentation-produced chymosin (FPC) used by cheese producers does
not contain any GM component or ingredient. FPC is identical with chymosin made
by an animal, but is produced in a more efficient way. FPC products have been
on the market since 1990 and have been considered in the last 20 years the
ideal milk-clotting enzyme.[5]
FPC was the first artificially
produced enzyme to be registered and allowed by the US Food and Drug Administration.
In 1999, about 60% of US hard cheese
was made with FPC[6]
and it has up to 80% of the global market share for rennet.[7]
By 2008, approximately 80% to 90% of
commercially made cheeses in the US and Britain were made using FPC.[1]
Today, the most widely used Fermentation-Produced Chymosin (FPC) is produced
either by the fungus Aspergillus niger and commercialized under the trademark CHY-MAX®[8]
by the Danish company Chr. Hansen, or produced by Kluyveromyces lactis and commercialized under the trademark MAXIREN®[9]
by the Dutch company DSM.
FPC is chymosin B, and is therefore
more pure compared with animal rennet, which contains a multitude of proteins.
FPC can deliver several benefits to the cheese producer compared with animal or
microbial rennet, such as higher production yield, better curd texture and
reduced bitterness.[5]
Cheeses produced with FPC can be
certified kosher[10][11]
and halal,[11]
and are suitable for vegetarians if there was no animal-based alimentation used
during the chymosin production in the fermenter.
Acid
coagulation
Cream cheese, paneer, and rubing are traditionally made this way (see Category:Acid-set
cheeses for others). The acidification can also
come from bacterial fermentation such as in cultured milk.[citation needed]
The entire wiki link on the subject can be found at: http://en.wikipedia.org/wiki/Rennet
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