Food Biochemistry and Food Processing (2 edition)

BLBS102-c23 BLBS102-Simpson March 21, 2012 13:44 Trim: 276mm X 219mm Printer Name: Yet to Come

434 Part 4: Milk

Figure 23.1.Processing scheme for natural cheeses.

contain unknown numbers of strains of the same species, are

used. Mesophilic L cultures containLeuconostocspecies, in-

cludingLn. mesenteroidesssp.cremorisandLn. lactis,while the

main species in mesophilic D culturesLactococcus lactisssp.

cremoriswith lesser amounts ofLc. lactisssp.lactis.Mesophilic

DL cultures would consist of both lactococci and leuconostoc.

The thermophilic cultures consist ofS. thermophilus, and ei-

therLactobacillus helveticus, Lb. delbrueckiissp.lactisorLb.

delbrueckiissp.bulgaricus.

Cutting the Coagulum Cutting the coagulum increases the

drainage of the whey from the curds and contributes to a sharp

decrease in the moisture content of the curds. Acid-coagulated

and rennet-coagulated cheeses differ in the pH at which curd for-

mation occurs, and subsequently the pH at which the coagulum

is cut. For acid-coagulated cheeses, curd formation occurs at

pH 4.6, the isoelectric point of casein. Curd formation of rennet-

coagulated cheeses occurs at higher pHs, ranging from pH 6.3 to

6.6. Following the cutting of the coagulum, the curd and whey

mixture is heated and agitated in a process called “scalding.”

The agitation is necessary to keep the curds suspended in the

whey and to promote drainage of whey from the curds. The tem-

perature during the scalding process is dependent on the type of

the cheese and ranges from 20◦Cto55◦C. The temperature af-

fects gel formation, gel viscoelasticity, and regulates the growth

of the lactic acid bacteria. A high temperature results in greater

drainage from the cheese and a firmer cheese.

The conversion of lactose to lactic acid by starter cultures

decreases the pH of the curd, which contributes to the loss of

the whey from the curd and a decrease in moisture content.

While the curds are in the whey, diffusion of lactic acid into

the whey and lactose into the curds occurs. The rate of acid

production is affected by the amount and type of the starter

cultures, composition of the milk, and temperature during acid

production.

When the required acidity of the cheese curds is reached, the

whey is drained to recover the curds. Following the separation

of the curds from the whey, acid production continues at an

increased rate, because of the lack of diffusion of the lactic acid

from the curd. To minimize excess acid development following

the drainage of the whey, some types of cheese include a washing

step to reduce the lactose content. The moisture content of the

curd is affected by the extent the coagulum is cut, the temperature

of the curd after cutting, and agitation of the curd in the whey.

The handling of the curd following the cutting of the coagulum

greatly affects the characteristics of the cheese. The cheddaring

process, used in the manufacture of Cheddar, Colby, Monterey,

and Mozzarella cheeses, involves piling blocks of curd on top

of each other with regular turning to allow the curds to fuse

together. In Colby and Monterey cheeses, vigorous stirring dur-

ing the drainage of the whey inhibits the development of a curd

structure and results in the softer cheese with a higher moisture

content. Frequently, the whey may be partially drained off and

replaced with water or salt brine to remove lactose and reduce

the development of acidity, as is done in the processing of Gouda

and Limburger cheeses.

Shaping and Pressing The resulting curds are shaped to form

a coherent mass that is easy to handle. The curds are placed in

a mold and are often pressed with an external force to cause

the curds to deform and fuse. The pressure and time of pressing

range from a few g/cm^2 for a few minutes for moist cheeses,

to 200 to 500 g/cm^2 for up to 16–48 hours for cooked and hard

cheeses. The temperature (20–27◦C) and humidity (95% relative

humidity) of the pressing room is controlled to optimize the

growth of the lactic acid bacteria and facilitate the deformation

and shaping of the curd. Acid production by lactic acid bacteria

and additional drainage of whey from the curd continues during

the shaping and pressing stage. The deformability is affected by

the composition of the cheese, and increases until the curds reach

a pH of 5.2–5.3. Deformability also increases with an increase

in moisture content and temperature.