Microbiology of Fermented Food Production ◾ 181
◾ Spoilage. Because of high moisture and low acid content, spoilage of psychrotrophic bacteria
(such as Pseudomonas spp.), yeasts, and molds can grow during storage. Preservatives, such
as sorbates, can be used to extend shelf life under refrigerated storage (also see Chapter 19).
Microbiology of Cheddar Cheese 7
Characteristics
Cheddar cheese is made from whole milk, contains less than 39% moisture, 48% fat, is generally
orange-yellow in color (a result of added color, annatto), and ripened. Smoothness of texture and
intensity of characteristic flavor vary with the starters used and the period of ripening. The typical flavor is the result of a delicate balance among flavor components produced during ripening
through enzymatic breakdown of carbohydrates, proteins, and lipids in unripened cheddar cheese.
Processing
1. Pasteurized; color (annatto) and starter added.
2. Incubated at 86°F (30°C) for acidity to increase by 0.2%; rennet added.
3. Incubated for coagulation (ca. 30 min) and cut in cubes.
4. Cooked at 100°F (37.8°C), whey drained, cheddaring to lose whey and curd to mat.
5. Milled, salted, put in form, pressed for 16 h to drain whey, and removed.
6. Dried for 5 days at 50°F (10°C), waxed, vacuum packaged, and cured at 40°F (4.4°C) for
2–12 months.
Starters (Controlled Fermentation)
Starters are selected mixed strains of Lac. lactis ssp. cremoris or lactis. Leuconostoc, which may be
added for flavor. Starters can be used as frozen concentrates (direct vat set).
Growth
Growth is accomplished by incubation at 86°F (30°C) for mesophilic starters to start early growth
and produce lactic acid to a 0.2% level by 60 minutes. This is important for the coagulation of
casein to occur rapidly following the addition of rennin. During curing, cells of the starter (also of
secondary flora) slowly die and release intracellular enzymes into the cheese.
Biochemistry
A large number of biochemical reactions occur during the different stages of processing, from the
initial incubation to the end of ripening, many not yet properly understood. Some are described
here.
Initially, lactose metabolism produces lactic acid as well as some diacetyl, acetate, ethanol, and
acetaldehyde, especially under aerobic conditions. Rennin destabilizes casein to produce paracasein that coagulates at low acidity and low temperatures. In addition, extracellular proteinases
and peptidases of the starter cultures metabolize milk proteins to peptides and amino acids and
transport them into the cells. Normally very little, if any, lipolysis occurs as a result of microbial
growth.
◾ Spoilage. Because of high moisture and low acid content, spoilage of psychrotrophic bacteria
(such as Pseudomonas spp.), yeasts, and molds can grow during storage. Preservatives, such
as sorbates, can be used to extend shelf life under refrigerated storage (also see Chapter 19).
Microbiology of Cheddar Cheese 7
Characteristics
Cheddar cheese is made from whole milk, contains less than 39% moisture, 48% fat, is generally
orange-yellow in color (a result of added color, annatto), and ripened. Smoothness of texture and
intensity of characteristic flavor vary with the starters used and the period of ripening. The typical flavor is the result of a delicate balance among flavor components produced during ripening
through enzymatic breakdown of carbohydrates, proteins, and lipids in unripened cheddar cheese.
Processing
1. Pasteurized; color (annatto) and starter added.
2. Incubated at 86°F (30°C) for acidity to increase by 0.2%; rennet added.
3. Incubated for coagulation (ca. 30 min) and cut in cubes.
4. Cooked at 100°F (37.8°C), whey drained, cheddaring to lose whey and curd to mat.
5. Milled, salted, put in form, pressed for 16 h to drain whey, and removed.
6. Dried for 5 days at 50°F (10°C), waxed, vacuum packaged, and cured at 40°F (4.4°C) for
2–12 months.
Starters (Controlled Fermentation)
Starters are selected mixed strains of Lac. lactis ssp. cremoris or lactis. Leuconostoc, which may be
added for flavor. Starters can be used as frozen concentrates (direct vat set).
Growth
Growth is accomplished by incubation at 86°F (30°C) for mesophilic starters to start early growth
and produce lactic acid to a 0.2% level by 60 minutes. This is important for the coagulation of
casein to occur rapidly following the addition of rennin. During curing, cells of the starter (also of
secondary flora) slowly die and release intracellular enzymes into the cheese.
Biochemistry
A large number of biochemical reactions occur during the different stages of processing, from the
initial incubation to the end of ripening, many not yet properly understood. Some are described
here.
Initially, lactose metabolism produces lactic acid as well as some diacetyl, acetate, ethanol, and
acetaldehyde, especially under aerobic conditions. Rennin destabilizes casein to produce paracasein that coagulates at low acidity and low temperatures. In addition, extracellular proteinases
and peptidases of the starter cultures metabolize milk proteins to peptides and amino acids and
transport them into the cells. Normally very little, if any, lipolysis occurs as a result of microbial
growth.