180 ◾ Fundamental Food Microbiology
− Swiss cheese with starters Str. thermophilus, Lab. helveticus, and dairy Propionibacterium
spp.; enterococci can be secondary (or associative) flora.
− Only cottage, Cheddar, Swiss, and blue cheeses are further discussed to understand the
microbiological aspects of unripened and ripened cheeses.
Microbiology of Cottage Cheese 7
Characteristics
Cottage cheese is made from low-fat or skim milk and has a soft texture with approximately 80%
moisture. It is unripened and has a buttery aroma resulting from diacetyl (along with lactic acid
and little acetaldehyde).
Processing (from Skim Milk)
1. Pasteurized, cooled to 70°F (22.2°C), starter added, and incubated for 12 h at pH 4.7.
2. Firm curd set, cut in cubes, and cooked at 125°F (51.7°C) for 50 min or more.
3. Whey drained off, stirred to remove more to get dry curd.
4. Salted, creamed, and preservative added.
5. Packaged and refrigerated.
Starters (Controlled Fermentation)
Frozen concentrate for direct vat set can be used. Mixed strains of Lac. lactis ssp. cremoris and lactis
are predominantly used for acid. Leu. mesenteroides ssp. cremoris can be added initially (in which
case citrate is added to milk), mainly for diacetyl. Lac. lactis ssp. lactis biovar diacetylactis can be
used for diacetyl but not inoculated in milk because of formation of too much CO 2 that causes
curd particles to float. Instead, it is grown separately in cream, which is then used to cream the
dry curd.
Growth, Biochemistry, and Genetics
Growth, biochemistry, and genetics (including current strain improvements) are similar to those
described for the microbiology of buttermilk (see section on microbiology of cultured buttermilk
fermentation).
Microbial Problems
◾ Slow growth. Weak or loss of Lac + phenotype, phage attack or less viable cells in frozen concentrate, antagonistic effect among starter strains for reasons described previously.
◾ Floatation of curd. Caused by too much CO 2 production by flavor-producing starters.
◾ Harsh flavor. Caused by more acetaldehyde and less diacetyl production from metabolic
imbalance and reduced environment.
◾ Low yield. Caused by partial proteolysis of casein by heat-stable proteinases produced in
refrigerated raw milk by psychrotrophs, such as Pseudomonas spp.
◾ Flavor loss. Caused by reduction of diacetyl to acetoin in a reduced environment as well as by
growth of undesirable bacteria during storage, such as Pseudomonas spp.
− Swiss cheese with starters Str. thermophilus, Lab. helveticus, and dairy Propionibacterium
spp.; enterococci can be secondary (or associative) flora.
− Only cottage, Cheddar, Swiss, and blue cheeses are further discussed to understand the
microbiological aspects of unripened and ripened cheeses.
Microbiology of Cottage Cheese 7
Characteristics
Cottage cheese is made from low-fat or skim milk and has a soft texture with approximately 80%
moisture. It is unripened and has a buttery aroma resulting from diacetyl (along with lactic acid
and little acetaldehyde).
Processing (from Skim Milk)
1. Pasteurized, cooled to 70°F (22.2°C), starter added, and incubated for 12 h at pH 4.7.
2. Firm curd set, cut in cubes, and cooked at 125°F (51.7°C) for 50 min or more.
3. Whey drained off, stirred to remove more to get dry curd.
4. Salted, creamed, and preservative added.
5. Packaged and refrigerated.
Starters (Controlled Fermentation)
Frozen concentrate for direct vat set can be used. Mixed strains of Lac. lactis ssp. cremoris and lactis
are predominantly used for acid. Leu. mesenteroides ssp. cremoris can be added initially (in which
case citrate is added to milk), mainly for diacetyl. Lac. lactis ssp. lactis biovar diacetylactis can be
used for diacetyl but not inoculated in milk because of formation of too much CO 2 that causes
curd particles to float. Instead, it is grown separately in cream, which is then used to cream the
dry curd.
Growth, Biochemistry, and Genetics
Growth, biochemistry, and genetics (including current strain improvements) are similar to those
described for the microbiology of buttermilk (see section on microbiology of cultured buttermilk
fermentation).
Microbial Problems
◾ Slow growth. Weak or loss of Lac + phenotype, phage attack or less viable cells in frozen concentrate, antagonistic effect among starter strains for reasons described previously.
◾ Floatation of curd. Caused by too much CO 2 production by flavor-producing starters.
◾ Harsh flavor. Caused by more acetaldehyde and less diacetyl production from metabolic
imbalance and reduced environment.
◾ Low yield. Caused by partial proteolysis of casein by heat-stable proteinases produced in
refrigerated raw milk by psychrotrophs, such as Pseudomonas spp.
◾ Flavor loss. Caused by reduction of diacetyl to acetoin in a reduced environment as well as by
growth of undesirable bacteria during storage, such as Pseudomonas spp.