Milk, Fermentation, and Fermented and Nonfermented Dairy Products 165
An outbreak of Campylobacter enteritis in the state of Louisiana in 1995 where garlic butter was
incriminated led to studies on the fate of foodborne pathogens in butter with or without garlic. In one
study, garlic butter was inoculated with ca. 10
4 and 10
6 cfu/g of C. jejuni and held at 5 or 21
◦ C. At 5
◦ C,
the pathogen decreased to <10 cfu/g within 3 hours for two batches and within 24 hours for a third
batch.
81 In butter with no garlic, C. jejuni survived for 13 days at 5
◦ C. At 21
◦ C, the pathogen decreased
to <10 cfu/g within 5 hours for two preparations and to 50 cfu/g in 5 hours for the third.
81 Overall,
up to 10
5 cells were killed within a few hours in butter with garlic, but the organism could survive for
days in refrigerated butter. In another study, Salmonella, E. coli 0157:H7, and L. monocytogenes were
found not to grow in unsalted butter with or without 20% garlic when held at 4.4, 21, or 37
◦ C for up
to 48 hours.
1
Yogurt (yoghurt) is produced with a yogurt starter, which is a mixed culture of S. salivarius subsp.
thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in a 1:1 ratio. The coccus grows faster
than the rod and is primarily responsible for initial acid production at a higher rate than that produced
by either when growing alone, and more acetaldehyde (the chief volatile flavor component of yogurt)
is produced by L. delbrueckii subsp. bulgaricus when growing in association with S. salivarius subsp.
thermophilus (see reference 57). The coccus can produce about 0.5% lactic acid and the rod about
0.6–0.8% (pH of 4.2–4.5). However, if incubation is extended, pH can decrease to about 3.5 with lactic
acid increasing to about 2%.
32
The product is prepared either by reducing the water content of either whole or skim milk by at least
one-fourth (may be done in a vacuum pan following sterilization of milk), or by adding about 5% milk
solids followed by water reduction (condensing). The concentrated milk is then heated to 82–93
◦ C
for 30–60 minutes and cooled to around 45
◦ C.
54 The yogurt starter is now added at a level of around
2% by volume and incubated at 45
◦ C for 3–5 hours followed by cooling to 5
◦ C. The titratable acidity
of a good finished product is around 0.85–0.90%, and to get this amount of acidity the fermenting
product should be removed from 45
◦ C when the titratable acidity is around 0.65–0.70%.
11 Good
yogurt keeps well at 5
◦ C for 1–2 weeks. The coccus grows first during the fermentation followed by
the rod, so that after around 3 hours, the numbers of the two organisms should be approximately equal.
Higher amounts of acidity, such as 4%, can be achieved by allowing the product to ferment longer,
with the effect that the rods will exceed the cocci in number. The streptococci tend to be inhibited at
yogurt pH values of 4.2–4.4, whereas the lactobacilli can tolerate pH values in the 3.5–3.8 range. The
lactic acid of yogurt is produced more from the glucose moiety of lactose than the galactose moiety.
Goodenough and Kleyn
21 found only a trace of glucose throughout yogurt fermentation, whereas
galactose increased from an initial trace to 1.2%. Samples of commercial yogurts showed only traces
of glucose, but galactose varied from around 1.5% to 2.5%.
Freshly produced yogurt typically contains around 10
9 organisms/g, but during storage, numbers
may decrease to 10
6 /g, especially when stored at 5
◦ C for up to 60 days.
27 The rod generally decreases
more rapidly than the coccus. The addition of fruits to yogurt does not appear to affect the numbers
of fermenting organisms.
27 The International Dairy Federation norm for yogurt is 10
7 /g or above. In
one study, E. coli 0157:H7 did not survive in skim milk at pH 3.8, and the organism was inactivated
in yogurt, sour cream, and buttermilk similarly.
26
The antimicrobial qualities of yogurt, buttermilk, sour cream, and cottage cheese have been examined
by inoculating Enterobacter aerogenes and Escherichia coli separately into commercial products and
studying the fate of these organisms when the products were stored at 7.2
◦ C. A sharp decline of
both coliforms was noted in yogurt and buttermilk after 24 hours. Neither could be found in yogurt
generally beyond 3 days. Although the numbers of coliforms were reduced also in sour cream, they
were not reduced as rapidly as in yogurt. Some cottage cheese samples actually supported an increase
in coliform numbers, probably because the products had higher pH values. The initial pH ranges for
An outbreak of Campylobacter enteritis in the state of Louisiana in 1995 where garlic butter was
incriminated led to studies on the fate of foodborne pathogens in butter with or without garlic. In one
study, garlic butter was inoculated with ca. 10
4 and 10
6 cfu/g of C. jejuni and held at 5 or 21
◦ C. At 5
◦ C,
the pathogen decreased to <10 cfu/g within 3 hours for two batches and within 24 hours for a third
batch.
81 In butter with no garlic, C. jejuni survived for 13 days at 5
◦ C. At 21
◦ C, the pathogen decreased
to <10 cfu/g within 5 hours for two preparations and to 50 cfu/g in 5 hours for the third.
81 Overall,
up to 10
5 cells were killed within a few hours in butter with garlic, but the organism could survive for
days in refrigerated butter. In another study, Salmonella, E. coli 0157:H7, and L. monocytogenes were
found not to grow in unsalted butter with or without 20% garlic when held at 4.4, 21, or 37
◦ C for up
to 48 hours.
1
Yogurt (yoghurt) is produced with a yogurt starter, which is a mixed culture of S. salivarius subsp.
thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in a 1:1 ratio. The coccus grows faster
than the rod and is primarily responsible for initial acid production at a higher rate than that produced
by either when growing alone, and more acetaldehyde (the chief volatile flavor component of yogurt)
is produced by L. delbrueckii subsp. bulgaricus when growing in association with S. salivarius subsp.
thermophilus (see reference 57). The coccus can produce about 0.5% lactic acid and the rod about
0.6–0.8% (pH of 4.2–4.5). However, if incubation is extended, pH can decrease to about 3.5 with lactic
acid increasing to about 2%.
32
The product is prepared either by reducing the water content of either whole or skim milk by at least
one-fourth (may be done in a vacuum pan following sterilization of milk), or by adding about 5% milk
solids followed by water reduction (condensing). The concentrated milk is then heated to 82–93
◦ C
for 30–60 minutes and cooled to around 45
◦ C.
54 The yogurt starter is now added at a level of around
2% by volume and incubated at 45
◦ C for 3–5 hours followed by cooling to 5
◦ C. The titratable acidity
of a good finished product is around 0.85–0.90%, and to get this amount of acidity the fermenting
product should be removed from 45
◦ C when the titratable acidity is around 0.65–0.70%.
11 Good
yogurt keeps well at 5
◦ C for 1–2 weeks. The coccus grows first during the fermentation followed by
the rod, so that after around 3 hours, the numbers of the two organisms should be approximately equal.
Higher amounts of acidity, such as 4%, can be achieved by allowing the product to ferment longer,
with the effect that the rods will exceed the cocci in number. The streptococci tend to be inhibited at
yogurt pH values of 4.2–4.4, whereas the lactobacilli can tolerate pH values in the 3.5–3.8 range. The
lactic acid of yogurt is produced more from the glucose moiety of lactose than the galactose moiety.
Goodenough and Kleyn
21 found only a trace of glucose throughout yogurt fermentation, whereas
galactose increased from an initial trace to 1.2%. Samples of commercial yogurts showed only traces
of glucose, but galactose varied from around 1.5% to 2.5%.
Freshly produced yogurt typically contains around 10
9 organisms/g, but during storage, numbers
may decrease to 10
6 /g, especially when stored at 5
◦ C for up to 60 days.
27 The rod generally decreases
more rapidly than the coccus. The addition of fruits to yogurt does not appear to affect the numbers
of fermenting organisms.
27 The International Dairy Federation norm for yogurt is 10
7 /g or above. In
one study, E. coli 0157:H7 did not survive in skim milk at pH 3.8, and the organism was inactivated
in yogurt, sour cream, and buttermilk similarly.
26
The antimicrobial qualities of yogurt, buttermilk, sour cream, and cottage cheese have been examined
by inoculating Enterobacter aerogenes and Escherichia coli separately into commercial products and
studying the fate of these organisms when the products were stored at 7.2
◦ C. A sharp decline of
both coliforms was noted in yogurt and buttermilk after 24 hours. Neither could be found in yogurt
generally beyond 3 days. Although the numbers of coliforms were reduced also in sour cream, they
were not reduced as rapidly as in yogurt. Some cottage cheese samples actually supported an increase
in coliform numbers, probably because the products had higher pH values. The initial pH ranges for