Preparation of yoghurt

yogurt preparation with milk by using Lactobacillus bulgaricus and Streptococcus thermophillus

1. Preparation of
yoghurt
Bangaru. karthik
Dept .of microbiology

2. Introduction
•Fermented milk product
•Word yoghurt comes from turkish word
“jugurt”

3. Mostly made from……
•Normal milk
•Skimmed milk
•Fortified milk

4. Milk source
•Mostly from cow
•Rarely from goat and sheep
•Limitation: milk should be free from
antimicrobial substance

5. Milk used in preparation
•Whole milk
•Partially defatted milk
•Condensed skimmed milk
•Cream
•Non fat dry milk
•Milk is condensed by removing 15-20% of
water in vaccum pan
•Milk fat levels are 1-3.25%

6. Limitation of milk
•Infected milk is not used

7. Additives permitted
•Nutritive carbohydrate sweetners
•Coloring agents
•Stabilizers
•Fruit preparation for flavouring yoghurt

8. Starter culture
•Lactobacillus bulgaricus
•Streptococcus thermophillus

9. Sweeteners
•Majorly used : Sucrose
•Others : corn sweetners and honey
•The level of sucrose effects preparation
–Production of lactic acid
–Flavour of yoghurt

10. Sucrose…..
•It can be added either in
–wet form
– dry form
–Granulated from
–Free flowing form
–Crystalline or liquid form
–67% of sucrose can be added

11. Other sweeteners
•Non- nutritive sweetners eg: ca-saccharin
•Lactose, glucose & galactose is also
suggested
•Commercial yoghurt have
–4.06% lactose
–1.85% galactose
–0.05% glucose
–pH = 4.1

12. Stabilizers
•Main function :
•Smoothness in body and texture
•To impart gel structure
•To reduce wheying off
•Increase the shelf life
•Provides a degree of uniformity

13. Charecters of a good stabilizer
•Should never effect flavour
•Should be effective at low pH
•Should be easily dispersed

14. Different stabilizers
•Gelatin
•Sea weed gums
•Algin & sodium alginate
•carrageenan

15. Fruit preparations in yoghurt
•Different fruit preparation are blended to
satisfy market requirement
•Generally 15-20% of low levels of fruit are
present
•Depending on their usage yoghurt is
classified into three types

16. Different types of yoghurt
•Eastern sundae style
•Western sundae style
•Swiss style yoghurt

17. Eastern sundae style
•Also called fruit on bottom
•59ml of fruit preserves at bottom followed
by 177ml of inoculated yoghurt mix
•No flavour or sweetners are added

18. Western sundae style
•Fruit preserves or special fruit preparations
forms the bottom layer
•Top layer has yoghurt containing sweetners
with the flovour and color
•It is identical to eastern sundae style
•Flavor level is usually 2-4% in the top layers

19. Swiss style yoghurt
•Also known as continental style or french
style or stirred yoghurt
•Fruit preparation is thoroughly blended in
yoghurt

20. Fruits used are….
•Strawberry
•Raspberry
•Bluberry
•Apples, peaches, orange, lemon

21. Starter culture
•Important in preparation
•Should be…
•Free from contaminants
•Vigorous growth in yoghurt mix
•Good flavour
•Body and texture production
•Resonable resistance to pahges and antibiotics

22. Starter cultures used are….
•Lactobacillus bulgaricus
•Streptococcus thermophilus

23. •Starter culture
–Gives flavor and texture production

24. •The lactobacilli grows first and liberate the amino
acid glycine and histidine
•This stimulate the growth of streptococci
•Formation of lactic acid, acetaldehyde, acetic
acid and diacetyl decides the flavour of yoghurt
•Sterptococci lowers the pH to 5.5
•Then lactobacilli reduces pH still 3.8 – 4.4

25. •Homogenization and high fat content gives
smooth texture
•Gassiness in yoghurt is due to
contamination by some bacilli

26. Types of yoghurt
•Plain yoghurt
–Set type
–Stirred type
•Fruit flavored yoghurt
–Eastern sundae style
–Western sundae style

27. Set type yoghurt
Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 12.5%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C
Bulk starter
Packing container
Incubate container
At 43°C pH 4.5
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C

28. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10.5%
Stabilizers – 0.7%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C, pH 4.5
Bulk starter
Packing container
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Cool to 25 °C
Stirred type of yoghurt

29. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10 -12.5%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C
Bulk starter, fruit syrup
And color for western style
Packing container, 1 part fruit
& 3-4 parts yoghurt
Incubate container
At 43°C pH 4.5
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Sundae style

30. Low fat milk, skim milk,
non fat dry milk
Standardized yoghurt
Milk fat – 1-2%
MSNF – 10.5%
Stabilizers – 0.7%
Pasteurize at 95°C
For 30 min
Homogenize at 60°C
Mix in holding VAT
43°C, pH 4.5
Bulk starter
Packing container
Cool & store plain
Yoghurt at 5°C upto
3-4weeks
Cool to
43°C
Swiss style
Cool to 25 °C
Yoghurt fruit is added