INTRODUCTION:
Cheese is a dairy product derived from milk and produced in wide ranges of flavors,
textures and forms by coagulation of milk protein casein. It comprises proteins and fat from milk, usually the milk of cows, buffalo, goats, or sheep. During production, the milk is usually acidified and the enzymes of rennet (or bacterial enzymes with similar activity) are added to cause the milk proteins (casein) to coagulate. The solids (curd) are separated from the liquid (whey) and pressed into final form. Some cheeses have aromatic molds on the rind, the outer layer, or throughout. Most cheeses melt at cooking temperature.
Cheese cultures
Cultures for cheese making are called lactic acid bacteria (LAB) because their primary source of energy is the lactose in milk and their primary metabolic product is lactic acid. There is a wide variety of bacterial cultures available that provide distinct flavor and textural characteristics to cheeses. Starter cultures are used early in the cheese making process to assist with coagulation by lowering the pH prior to rennet addition. The metabolism of the starter cultures contribute desirable flavor compounds, and help prevent the growth of spoilage organisms and pathogens. Typical starter bacteria include Lactococcus lactis subsp. lactis or cremoris, Streptococcus salivarius subsp. thermophilus, Lactobacillus delbruckii subsp. bulgaricus, and Lactobacillus helveticu.
Adjunct cultures are used to provide or enhance the characteristic flavors and textures of cheese. Common adjunct cultures added during manufacture include Lactobacillus casei and Lactobacillus plantarum for flavor in Cheddar cheese, or the use of Propionibacterium freudenreichii for eye formation in Swiss. Adjunct cultures can also be used as a smear for washing the outside of the formed cheese, such as the use of Brevibacterium linens of gruyere, brick and limburger cheeses.
Yeasts and molds are used in some cheeses to provide the characteristic colors and flavors of some cheese varieties. Torula yeast is used in the smear for the ripening of brick and limburger cheese. Examples of molds include Penicillium camemberti in camembert and brie, and Penicillium roqueforti in blue cheeses.
General steps in cheese preparation
The temperatures, times, and target pH for different steps, the sequence of processing steps, the use of salting or brining, block formation, and aging vary considerably between cheese types. General steps involved in cheese preparation include
Standardization of milk
Pasteurization of milk
Cooling of milk
Inoculation and Ripening
Addition of rennet and Curdling
Cutting of curd and Heat treatment
Draining of whey
Texture curd
Salting
Form Cheese into Blocks
Store and Age
Package
Standardization of Milk
Milk is often standardized before cheese making to optimize the
protein to fat ratio to make a good quality cheese with a high yield
Pasteurize of 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.
Cooling of 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).
Inoculation and Ripening:
The starter cultures and any non-starter adjunct bacteria are added to the milk and held at 90°F (32°C) for 30 minutes to ripen. The ripening step allows the bacteria to grow and begin fermentation, which lowers the pH and develops the flavor of the cheese.
Addition of rennet and Curdling:
The rennet is the enzyme that acts on the milk proteins to
form the curd. After the rennet is added, the curd is not disturbed for approximately 30
minutes so a firm coagulum forms.
Cutting of curd and Heat treatment:
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. The whey is drained from the vat and the curd forms a mat.
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.
Dry Salt or Brine:
For cheddar cheese, the smaller, milled curd pieces are put back in the vat
and salted by sprinkling dry salt on the curd and mixing in the salt. In some cheese varieties,
such as mozzarella, the curd is formed into loaves and then the loaves are placed in brine (salt
water solution).
Packing and storage:
: The salted curd pieces are placed in cheese hoops and pressed into
blocks to form the cheese. 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. Cheese
may be cut and packaged into blocks or it may be waxed.