Preparation of yoghurt

Bangaru. karthikDept .of microbiology

Introduction

• Fermented milk product

• Word yoghurt comes from turkish word “jugurt”

Mostly made from……

• Normal milk

• Skimmed milk

• Fortified milk

Milk source

• Mostly from cow • Rarely from goat and sheep

• Limitation: milk should be free from antimicrobial substance

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%

Limitation of milk

• Infected milk is not used

Additives permitted

• Nutritive carbohydrate sweetners

• Coloring agents

• Stabilizers

• Fruit preparation for flavouring yoghurt

Starter culture

• Lactobacillus bulgaricus

• Streptococcus thermophillus

Sweeteners

• Majorly used : Sucrose• Others : corn sweetners and honey

• The level of sucrose effects preparation– Production of lactic acid– Flavour of yoghurt

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

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

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

Charecters of a good stabilizer

• Should never effect flavour

• Should be effective at low pH

• Should be easily dispersed

Different stabilizers

• Gelatin

• Sea weed gums

• Algin & sodium alginate

• carrageenan

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

Different types of yoghurt

• Eastern sundae style

• Western sundae style

• Swiss style yoghurt

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

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

Swiss style yoghurt

• Also known as continental style or french style or stirred yoghurt

• Fruit preparation is thoroughly blended in yoghurt

Fruits used are….

• Strawberry• Raspberry• Bluberry• Apples, peaches, orange, lemon

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

Starter cultures used are….

• Lactobacillus bulgaricus• Streptococcus thermophilus

• Starter culture

– Gives flavor and texture production

• 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

• Homogenization and high fat content gives smooth texture

• Gassiness in yoghurt is due to contamination by some bacilli

Types of yoghurt

• Plain yoghurt– Set type – Stirred type

• Fruit flavored yoghurt– Eastern sundae style – Western sundae style

Set type yoghurt

Low fat milk, skim milk, non fat dry milk

Standardized yoghurtMilk fat – 1-2%MSNF – 12.5%

Pasteurize at 95°CFor 30 min

Homogenize at 60°C

Mix in holding VAT43°C

Bulk starter

Packing container

Incubate containerAt 43°C pH 4.5

Cool & store plain Yoghurt at 5°C upto

3-4weeks

Cool to 43°C

Low fat milk, skim milk, non fat dry milk

Standardized yoghurtMilk fat – 1-2%MSNF – 10.5%

Stabilizers – 0.7%

Pasteurize at 95°CFor 30 min

Homogenize at 60°C

Mix in holding VAT43°C, pH 4.5

Bulk starter

Packing container

Cool & store plain Yoghurt at 5°C upto

3-4weeksCool to 43°C

Cool to 25 °C

Stirred type of yoghurt

Low fat milk, skim milk, non fat dry milk

Standardized yoghurtMilk fat – 1-2%

MSNF – 10 -12.5%

Pasteurize at 95°CFor 30 min

Homogenize at 60°C

Mix in holding VAT43°C

Bulk starter, fruit syrupAnd color for western style

Packing container, 1 part fruit& 3-4 parts yoghurt

Incubate containerAt 43°C pH 4.5

Cool & store plain Yoghurt at 5°C upto

3-4weeks

Cool to 43°C

Sundae style

Low fat milk, skim milk, non fat dry milk

Standardized yoghurtMilk fat – 1-2%MSNF – 10.5%

Stabilizers – 0.7%

Pasteurize at 95°CFor 30 min

Homogenize at 60°C

Mix in holding VAT43°C, pH 4.5

Bulk starter

Packing container

Cool & store plain Yoghurt at 5°C upto

3-4weeksCool to 43°C

Swiss style

Cool to 25 °C

Yoghurt fruit is added