Microbiology of Fermented Food Production ◾ 173
storage of raw milk before pasteurization (see Chapter 22). These enzymes remain stable after heating and can cause product defects (low yield of cheese, proteolysis, and rancidity). Before milk is
used for fermentation, these aspects need to be considered.
Fermented Milk Products
Many types of fermented milk products are produced in different parts of the world. A few are
produced by controlled fermentation, and the microbial types and their respective contributions
are known. In many others, fermented either naturally or by back slopping, the microbial profiles
and their contributions are not exactly known. Many types of lactic acid bacteria and some yeasts
are found to predominate microbial flora in these products, 3,4 some of which are listed:
1. Buttermilk. Made with Lactococcus species without or with Leuconostoc cremoris; some can
have biovar diacetylactis in place of Leu. cremoris (such as ymer in Denmark), whereas some
can have a ropy variant of Lactococcus species (langfil in Norway) or mold (Geotrichum candidum in villi in Finland).
2. Yogurt. Made with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus;
some types can also have added Lab. acidophilus, casei, rhamnosus, and Bifidobacterium spp.;
some may also have Lactococcus species and Lab. plantarum and lactose-fermenting yeasts
(dahi in India).
3. Acidophilus milk. Made with Lab. acidophilus.
4. Bifidus milk. Made with Bifidobacterium spp.
5. Yakult. Made with Lab. casei; may contain Bifidobacterium spp.
6. Kefir. Made from Lab. kefir (several species of yeasts along with Leuconostoc, Lactobacillus,
and Lactococcus spp.).
7. Kumiss. Made from Lab. delbrueckii subsp. bulgaricus and yeasts.
Among these, cultured buttermilk and yogurt are discussed here.
Microbiology of Cultured Buttermilk Fermentation
It is produced from partially skim milk through controlled fermentation with starter cultures.
Product Characteristics
Buttermilk should have a pleasant acidic taste (from lactic acid) and a high degree of aroma (from
diacetyl) with a slight effervescence (from CO 2 ). It should have a white color with a smooth, thick
body and should pour easily.
Processing
1. Skim milk ≥9% SNF (solid nonfat) + citrate (0.2%)
2. Heated at 185°F (85°C) for 30 min (kills bacterial cells and phages)
3. Cooled to 72°F (22°C), starter added, agitated for 50 min (incorporates air)
4. Incubated at 72°F (22°C) for 12 h, pH 4.7, acidity 0.9%
5. Gel broken, cooled to 40°F (4.5°C), and salted (package)
storage of raw milk before pasteurization (see Chapter 22). These enzymes remain stable after heating and can cause product defects (low yield of cheese, proteolysis, and rancidity). Before milk is
used for fermentation, these aspects need to be considered.
Fermented Milk Products
Many types of fermented milk products are produced in different parts of the world. A few are
produced by controlled fermentation, and the microbial types and their respective contributions
are known. In many others, fermented either naturally or by back slopping, the microbial profiles
and their contributions are not exactly known. Many types of lactic acid bacteria and some yeasts
are found to predominate microbial flora in these products, 3,4 some of which are listed:
1. Buttermilk. Made with Lactococcus species without or with Leuconostoc cremoris; some can
have biovar diacetylactis in place of Leu. cremoris (such as ymer in Denmark), whereas some
can have a ropy variant of Lactococcus species (langfil in Norway) or mold (Geotrichum candidum in villi in Finland).
2. Yogurt. Made with Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus;
some types can also have added Lab. acidophilus, casei, rhamnosus, and Bifidobacterium spp.;
some may also have Lactococcus species and Lab. plantarum and lactose-fermenting yeasts
(dahi in India).
3. Acidophilus milk. Made with Lab. acidophilus.
4. Bifidus milk. Made with Bifidobacterium spp.
5. Yakult. Made with Lab. casei; may contain Bifidobacterium spp.
6. Kefir. Made from Lab. kefir (several species of yeasts along with Leuconostoc, Lactobacillus,
and Lactococcus spp.).
7. Kumiss. Made from Lab. delbrueckii subsp. bulgaricus and yeasts.
Among these, cultured buttermilk and yogurt are discussed here.
Microbiology of Cultured Buttermilk Fermentation
It is produced from partially skim milk through controlled fermentation with starter cultures.
Product Characteristics
Buttermilk should have a pleasant acidic taste (from lactic acid) and a high degree of aroma (from
diacetyl) with a slight effervescence (from CO 2 ). It should have a white color with a smooth, thick
body and should pour easily.
Processing
1. Skim milk ≥9% SNF (solid nonfat) + citrate (0.2%)
2. Heated at 185°F (85°C) for 30 min (kills bacterial cells and phages)
3. Cooled to 72°F (22°C), starter added, agitated for 50 min (incorporates air)
4. Incubated at 72°F (22°C) for 12 h, pH 4.7, acidity 0.9%
5. Gel broken, cooled to 40°F (4.5°C), and salted (package)