Fermented milk products
Fermented milks are products prepared from milks (whole,
partially or fully skimmed milk, concentrated milk or milk
reconstituted from partially or fully skimmed dried milk), homogenized
or not, pasteurized or sterilized and fermented by means of specific
Now a day a wide range of fermented milks is produced. They
differ in aroma and flavour, fat content, presence of a variety of fruits
Fermented milks are popular products used allover the world, its
popularity due to its therapeutic value, simple technology for
production, low cost and long shelf-life.
Therapeutic value of fermented milks:
(1) High-acid producing organisms suppressed toxin-producing
bacteria in the large intestine of the human and prevented
putrefaction and autointoxication of the individual.
(2) Alleviation of lactose mal-digestion by the reduction of lactose
content in the product and auto-digestion of lactose by the
acid producing organisms (starter) drive -glactosidase.
(3) Has anti-carcinogenic activity by removal of dietary procarcinogens and stimulation of host immune system. (it has
been suggested that some lactobacilli produce anticarcinogenic compounds and may metabolise and destroy
known carcinogens e.g. nitrosamines).
(4) Reducing blood cholesterol.
(5) Has nutritional enhancement by synthesis of B-complex
vitamin and increased calcium absorption.
(6) Recently researches have discovered acidophilin, lactocidin,
lactolin, nisin and diplococcin which are types of antibiotics
produced by bacteria used in milk fermentation. So, it can be
used for liver complaints, T.B. and renal malfunction because
it reduces level of toxic amines.
(7) Fermented milks used as modern comestics.
Types of fermented milks:
Distinct forms of fermented milks exits, although many are
similar with respect to technology. Fermented milks may be
classified according to the type of starter microorganism used
which give specific taste or uses.
(1) Mesophilic lactic fermentation:
a. Cultured butter milk
b. Cultured cream
(2) Thermophilic lactic fermentation
(3) Therapeutic lactic fermentation
a. Acidophillus milk
(4) Lactic yeast fermentation
(1) Cultured buttermilk: (Bulgarian fermented milk)
The name (buttermilk) is used to denote that product
separated after churning fermented cream into butter. It is a short
shelf life product. The modern substituent is cultured buttermilk. It
is prepared from pasteurized skim or whole milk that has been
fermented by a lactic culture and by aroma bacteria (Strept. lactis,
Strept. diacetylactis, Strept. cremoris and Lact. citrovorum)
Milk is heated to about 88 0C with homogenization for 30
minutes and cooling to 20-25 0C before addition of starter, which is
added at a level of 1-2 %, fermentation proceeding for 16-20 hours
at 25 0C to an acidity 0.9 % lactic acid, gelatin is sometimes added
(2) Cultured cream:
Cultured or sour cream is acid gel of delicate flavour resulting
from the growth and activity of lactic acid streptococci and flavourproducing leuconostoc bacteria in light cream. Cultured cream is
used on salads, as a dressing for vegetables, in filling for cakes or
consumed directly. The fat content of cultured cream is
standardized between 12-30 % depending on the required
properties. The starter culture is similar to that used for culture is
similar to that used for cultured buttermilk.
Cream is heated to 82 0C for 30 minutes. It is homogenized
while hot, then cooled to about 21 0C and inoculated with 0.5-1 %
of butter starter. Incubation is continued at 21 –25 0C for 8-14
hours until the acidity reaches about 0.6 % lactic acid.
(3) Yoghurt (Yogurt, Dahi, Zabady):
It is the most common type of fermented milks consumed in
our country. It is delicious, agreeable in consistency, and high in
nutritive value and of good flavour.
High quality raw milk must be used, heated at 80-85 0C for
20-30 minutes or at 95 0C for 10 minutes, then cooled to about 48
0C and inoculated with 2-3 % of yoghurt culture (Lactobacillus
bulgaricus and Streptococcus thermophillus 1:1) and incubate at
44-45 0C (42 0C) for about 3 hours tell formation of a firm gel curd
and the pH is 4.6-4.8 and titratable acidity 0.85 – 0.90 % is
The yoghurt is cooled to about 5 0C, in refrigerator and held at
this temperature until distributed to the consumer. Under these
condition the product can be kept satisfactory for 1-2 weeks.
Traditionally the product was made from milk concentrated by
boiling, in practice the treatment applied varies from HTST
pasteurization to a full UHT process. Such treatment is recommended: To denatures the whey proteins, which increase the
capacity of dairy mass to bind water and subsequently improves the
texture (increase the total solids (8.5-15 %), to kill all pathogenic
bacteria and high percentage of saprophytic ones.
Types of yoghurt:
(1) Plain yoghurt (natural yoghurt)
Produced from milk and starter culture only without any
addition of additives.
(2) Flavoured yoghurt:
Sugar, fruit concentrates various essences such as vanilla and
natural colors used in this type of yoghurt.
Yoghurt is recommended as a replacement for milk in
the diet of persons suffering from lactose intolerance,
because the fermentation of lactose by the action of
lactic acid bacteria (starter) lower the lactose content
There are other forms of yoghurt e.g.
1. Drinking yoghurt
2. Dried yoghurt
3. Frozen yoghurt.
(4) Acidophillus milk:
It is produced by lactobacillus acidophillus bacteria which they
have the ability to implant themselves in the large intestines.
This type of fermented milk is prescribed for patients with
various stomach disorders including constipation, nonulcerative colitis and diarrhea.
Skim milk or partially de-fatted milk or whole milk is sterilized
in an autoclave at 120 0C for 20 minutes, then cooled to 38 0C.
5 % inoculation of active Lactobacillus acidophilus starter is
The mixture is incubated at 38 0C for 18-24 hours until a curd
forms with about 1 % titratable acidity
It is cooled to 10 0C before agitating and pumped to a filler and
The acidophilus milk is chilled to 4 0C and distributed rapidly.
Kefir originated in the Caucasian Mountains.
It is made from the milk of the goats, sheep, or cow.
The distinctive feature of kefir is the application of “Kefir
grains” to sustain the fermentation.
Kefir grains are lyophilized cultures, gelatinous whitish or
yellowish, irregular granules about the size of a walnut or
wheat grains, in which bacteria and yeast cells exist together
symbiotically. They are insoluble in water and ordinary solvents. When it is immersed in milk it swell and turn white,
and initiate the dual lactic acid and alcohol fermentation.
The dominant microbial flora of kefir consists of Saccharomyces
kefir, Torula kefir, Lactobacillus caucasicus, Leuconostoc spp.
and Lactic acid streptococci. Yeast represent 5 to 10 % of
Whole milk is pasteurized at 85 0C for 30 minutes and cooled to
Kefir grains then seeded into this milk which is inoculated at 20
– 25 0C for 20 hours.
The curdled milk is strained through a clean wire sieve to
recover the grains, then chilled and the milk is ready for
A good kefir milk foams and fizzes like beer, it is foamy
effervescent drink with lactic acid about 0.8-1%, ethyl alcohol 1
% and carbon dioxid.
It is lactic acid-alcohol fermented milk of considerable
commercial and public health significance to Russia.
It is made from mar’s milk, but similar products are made from
whole or skimmed cow’s milk.
Milk is pasteurized to 70 0C for 30 minutes and cooled to 30 0C.
A 10 % culture containing Lact. bulgaricus, Lact. acidophilus
and Saccharomyces lactis is added to milk with 2.5 % beet
The mixture is incubated at 27 0C until firm curd forms with
titratable acidity of 0.8 %, then stirred and bottled, cooled to 4
The acidity and ethanol content differ according to the
incubation period from 12 hours to 1-3 days, acidity ranges
from 0.6 % to 1 % lactic acid and ethanol ranges from 0.7 % to
This type of fermented milk in Russia used for treatment of
Defects and spoilage of fermented milks:
(1) Excessive whey:
It is due to:
Insufficient heating of milk to evaporate ¼ of its water percent
i.e. heated at low temperature or short time of heating.
Short period of incubation.
(2) Excessive acidity:
It occurs due to
Addition of more starter.
Long period of incubation
Failing of cooling after incubation.
Store at relatively high temperature or exposure to sunlight.
It is due to:
Impurity of starter (bad quality starter) which gives abnormal
flavour due to presence of saprophytic bacteria and coliforms.
Insufficient heating of milk.
Contamination of formed fermented milk with different
Absorption of different surrounded abnormal odour.
It is due to:
Death of starter microorganisms and release of proteolytic
Contamination of fermented milk with proteolytic
(5) Yeast and mold growth:
(6) Soft curd:
It occurs due to:
Presence of antibiotics, pesticides and insecticides residue.
Insufficient heating of milk.
Calcium salt equilibrium (calcium defect).
Fermented milk as carriers of pathogens:
Although is it too acid to permit growth of most pathogens, sour
milk has incriminated in a few out-break of disease, such as
Salmonella, Shigella and Coliforms.
Yoghurt with large number of yeast leads to digestive troubles.