Industrial Biotechnology
Badr
Objectives

Be able to produces Cheddar Cheese.
I. Introduction
Cheddar cheese is a semi-hard cows milk cheese which can vary in taste from mild to
extra sharp. The cheese is one of the most well known cheeses in the world, and many
countries produce regional versions of cheddar cheese, especially Britain and former
colonies. Because of the fame of the cheese, it is readily available in most markets, and it
varies widely in quality.
Cheese is a highly proteinaceous food made from the milk of some herbivores.
Cheese is believed to have originated in the warm climates of the Middle East some
thousands of years ago, and is said to have evolved when milk placed in goat stomach
was found to have curdled. The scientific study and manipulation of milk for cheese
manufacture is however just over a hundred years old.
About a thousand types of cheese have been described depending on the properties
and treatment of the milk, the method of production, conditions such as temperature, and
the properties of the coagulum, and the local preferences.
II. Stages in the manufacture of cheese
II.1 Pasteurize/Heat Treat Milk
Depending on the desired cheese, the milk may be pasteurized or mildly heat-treated
to reduce the number of spoilage organisms and improve the environment for the starter
cultures to grow. Some varieties of milk are made from raw milk so they are not
pasteurized or heat-treated. Raw milk cheeses must be aged for at least 60 days to reduce
the possibility of exposure to disease causing microorganisms (pathogens) that may be
present in the milk.
II.1.1 Cool Milk
Milk is cooled after pasteurization or heat treatment to 90°F (32°C) to bring it to the
temperature needed for the starter bacteria to grow. If raw milk is used the milk must be
heated to 90°F (32°C).
II.1.2 Inoculate with Starter & Non-Starter Bacteria and Ripen
For cheese prepared at temperatures less than 40°C strains of Lactococcus lactis are
used. For those prepared at higher temperatures the more thermophilic Streptococcus
thermophilus, Lactobacillus bulgaricus, and Lact. helveticus are used.
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Industrial Biotechnology
Badr
Lactic acid has the following effects:
 It causes the coagulation of casein at pH 4.6, the isoelectric point of that protein,
which is used in the manufacture of some cheeses, e.g. cottage cheese.
 It provides a favorably low pH for the action of rennin the enzyme which forms
the curd from casein in other types of cheeses.
 The low pH eliminates proteolytic and other undesirable bacteria.
 It causes the curd to shrink and thus promotes the drainage of whey.
 Metabolic products from the lactic acid bacteria such as ketones, esters and
aldehydes contribute to the flavor of the cheese.
II.1.3 Adding of rennet for coagulum formation
Chymosin, rennet, and rennin are often used interchangeably to refer to this enzyme.
The latter, rennin, should not be confused with renin, which is an enzyme associated with
kidneys and does not clot milk. The rennet is the enzyme that acts on the milk proteins to
form the curd which is derived from the fourth stomach, abomasum of freshly
slaughtered milk-fed calves. Besides those of calves, the abomasum of kids (young
goats), lamb or other young mammals have been used.
II.1.3 .1 Production of natural calf rennet
1. Soaking and/or shredding air-dried vells under acid conditions with 12-20% salt.
Extracts from young calves contain 94% rennin and 6% pepsin and from older cows,
40% rennin and 60% pepsin.
2. Rennin (chymosin) is the enzyme responsible for the coagulation of the milk. Pepsin
is proteolytic and too high an amount of pepsin can result in the hydrolysis of the
coagulum and a resulting low yield of cheese, and a bitter taste may result from the
amino acids.
3. Due to the high cost of animal rennet, other sources, mostly of microbial origins,
have been found
II.1.3 .1.1 Rennet manufacture
Extraction of chymosin and production of rennet begin by extracting, for several
days,
1. Chopped or macerated stomachs with a 10% sodium chloride solution containing
about 5% boric acid or glycerol.
2. Additional salt up to a total of 16–18% is introduced followed by filtration and
clarification.
3. Mucine and grass particles in suspension are removed by introducing 1% of potash
alum, followed by an equal amount of potassium phosphate.
4. The suspension is adjusted to pH 5.0 to activate prochymosin (zymogen) to
chymosin, and the enzyme strength is standardized, so that one part coagulates
15,000 or 10,000 parts of milk.
5. Sodium benzoate, propyleneglycol, and salt are added as preservatives for the
II.1.3.2 Some commercial microbial rennets and their microbial sources
Substitutes from microbial sources have been very successful and continue to be
used. Many act like trypsin and have an optimum pH activity between 7 and 8.
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Industrial Biotechnology
Badr
Microorganisms, including Bacillus subtilis, B. cereus, B. polymyxa, and Mucor
pusillus t (also known as Rhizomucor pusillus) and Rh. miehei have been extracted for
their proteasenzymes. The bacilli enzyme preparations were not suited for cheese making
because of excessive proteolytic activity while the fungal-derived enzymes gave good
results, but not without off flavors such as bitter.
II.1.3.3 Vegetable rennet
Many plants have coagulating properties. Some examples include an extract of fig
juice to coagulate milk. Other examples include nettles, thistles, mallow, sunflowers.
The dried flowers of the species of sunflowers can also be used. Dry the blossoms and
grind them to powder with a mortar and pestle. Dissolve a couple of teaspoons of the
powder in one-half cup of water, then add the infusion to the milk the same as if using a
rennet solution.
III. Cut Curd and Heat
The curd is allowed to ferment until it reaches pH 6.4. The curd is then cut with
cheese knives into small pieces and heated to 100°F (38°C). The heating step helps to
separate the whey from the curd.
IV. Drain whey
The whey is drained from the vat and the curd forms a mat.
V. Texture curd
The curd mats are cut into sections and piled on top of each other and flipped
periodically. This step is called cheddaring. Cheddaring helps to expel more whey,
allows the fermentation to continue until a pH of 5.1 to 5.5 is reached, and allows the
mats to "knit" together and form a tighter matted structure. The curd mats are then milled
(cut) into smaller pieces.
VI. Dry Salt or Brine
For cheddar cheese, the smaller, milled curd pieces are put back in the vat and salted
by sprinkling dry salt (1% and 3% by weight) on the curd and mixing in the salt.
VII. Form Cheese into Blocks
The salted curd pieces are placed in cheese hoops and pressed into blocks to form the
cheese.
VIII. Store and Age
The cheese is stored in coolers until the desired age is reached. Depending on the
variety, cheese can be aged from several months to several years.
IX. Package
Cheese may be cut and packaged into blocks.
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