A starter culture is a culture of bacteria used to control the fermentation of milk. It is desirable because the natural microflora in milk can be unpredictable and inconsistent. A starter culture provides a controlled and predictable fermentation. There are different types of starter cultures defined by factors like the bacteria used, temperature optimum, physical form, and whether they contain single or multiple bacterial species. Proper preparation and maintenance of the starter culture is important to ensure it performs as intended in fermenting milk.

1. Starter Cultures
• Traditionally the fermenting organisms came from the natural
microflora or a portion of the previous fermentation.
• In many cases the natural microflora is either inefficient,
uncontrollable, and unpredictable, or is destroyed during preparation
of the sample prior to fermentation (e.g. pasteurization).
• A starter culture can provide particular characteristics in a more
controlled and predictable fermentation.

2. What is a starter culture and why use it?
• A starter culture is a milk product which:
• - contains lactic acid bacteria
• - controls the souring of milk.

3. Why use a starter culture?
• To control fermentation.
Raw milk always contains different microorganisms.
These microorganisms turn your milk sour but you cannot
control the fermentation.
Pasteurization kills most of these microorganisms.
By using a commercial starter culture with pasteurized milk, you
can control the souring of milk

4. Starter Cultures
• Lactic starters always include bacteria that convert sugars to
lactic acid, usually:
• Lactococcus lactis subsp. lactis,
• Lactococcus lactis subsp. cremoris or
• Lactococccus lactis subsp. lactis biovar diacetylactis.
• Where flavour and aroma compounds such as diacetyl are
desired the lactic acid starter will include heterofermentative
organisms such as:
• Leuconostoc citrovorum or
• Leuconostoc dextranicum.

5. What types of starter culture are there?
• There are many types of starter culture and we can group them in
different ways.
• - local conditions
• - the product you want to make.

6. Types of Starter Cultures
Optimum growth temperature
• Mesophilic cultures grow best at about 30 C.
• Thermophilic cultures grow best at about 43 C.

7. Types of Starter Cultures
Physical state
• Starter cultures can be:
• - liquids
• - solid (deep-frozen)
• - powders (freeze-dried)
Powder cultures are useful because:
- they have good keeping qualities (more than 6 months at -20 C)
- you can send them long distances by airmail.

8. Types of Starter Cultures
Pure/mixed
Pure cultures have one species of lactic acid bacteria.
Mixed cultures (more common) have two or more species.

9. Types of Starter Cultures
Type of lactic acid bacteria
• Some lactic acid bacteria produce only lactic acid.
• Others produce lactic acid gas and aromatic compounds.

10. Some common lactic acid bacteria used in cultures
are:
Mesophilic Thermophilic
Pure Pure Mixed
• Sc. lactis Sc. thermophilus Sc. thermophilus
• Sc. cremoris Lb. helveticus +
• Sc. diacetylactis Lb. bulgaricus Lb. bulgaricus
• Lc. cremoris Lb. acidophilus
Note:
• Sc. = Streptococcus, Lc. = Leuconostoc, Lb. = Lactobacillus

11. Starter Cultures
• The primary function of lactic starters is the production of
lactic acid from sugars
• Other functions of starter cultures may include the
following:
• flavour, aroma, and alcohol production
• proteolytic and lipolytic activities
• inhibition of undesirable organisms

12. How do you prepare and maintain a starter
culture?
• disinfected equipment, clean, sterilize and rinse with boiling water all
utensils before using.
• Any dirt or chemicals will change the action of the starter culture.
• the correct starter culture and high quality milk
• to do the right things at the right time.

13. A good starter CULTURE will:
• Convert most of the sugars to lactic acid
• Increase the lactic acid concentration to 0.8
to 1.2 % (Titratable acidity)
• Drop the pH to between 4.3 to 4.5