Yogurt

1
Yogurt

• A form of fermented milk produced in most
  countries where fresh milk is drunk.

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Yogurt

• Yogurt is produced by the controlled fermentation
  of milk by two species of bacteria Lactobacillus
  bulgaricus and Lactotococcus thermophilus (also
  known as Streptococcus thermophilus)

3
Yogurt

• The sugar in milk (called lactose) is fermented
  to acid (lactic acid) and it is this that causes
  the characteristic curd to form.

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Yogurt

• Streptococcus thermophilus brings the pH of the
  milk down to 5.5
• Lactobacillus bulgaricus converts lactose to
  lactic acid

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Yogurt

• The two bacteria have a mutually stimulating
  effect on one another.
• Proteolytic enzymes from L. bulgaricus break down
  milk proteins into peptides.

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Yogurt

• These peptides stimulate the growth of L.
  thermophilus which in turn produces formic acid
  and carbon dioxide
• These are growth stimulants for the L. bulgaricus.

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Yogurt

• At the end of the incubation pH may fall to as
  low as 4.2 4.4
• The lactic acid coagulates the remaining milk
  proteins, causing the yoghurt to thicken.

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Yogurt

• Acetaldehyde, a metabolic by product of both
  species, gives raw yoghurt its characteristic
  flavour.

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Yogurt

• Incubation takes 12 hours at 32o C to reach the
  set point of natural yoghurt
• Sugar, colour and fruit pulp is often added to
  increase popularity of product.

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Yogurt

• Yogurt is a nutritious dessert and its
  manufacture is an ideal way of using up Europes
  excess milk production

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Yogurt

• Some yoghurts may receive additional heat
  treatment to kill off any living bacteria before
  or after packaging for the consumer

12
peptides
proteins
13
peptides
proteins
Lactobacillus thermophilus
14
peptides
proteins
Proteolytic enzymes
Lactobacillus thermophilus
Lactobacillus bulgaricus
15
peptides
proteins
Proteolytic enzymes
Lactobacillus thermophilus
Lactobacillus bulgaricus
formic acid CO2
16
peptides
proteins
Proteolytic enzymes
Lactobacillus thermophilus
Lactobacillus bulgaricus
formic acid CO2
lactic acid
17
peptides
proteins
Proteolytic enzymes
Lactobacillus thermophilus
Lactobacillus bulgaricus
formic acid CO2
lactic acid
acetaldehyde
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Raw milk
19
Raw milk
pasteurisation
Pasteurised Milk
20
Raw milk
pasteurisation
Pasteurised Milk
homogenisation cooling incubation
add starter
Raw Yogurt
21
Raw milk
pasteurisation
Pasteurised Milk
homogenisation cooling incubation
add starter
Raw Yogurt
add fruit/flavour
(heat treatment) packaging (heat treatment)
Processed Yogurt