1. Starter Cultures Starter culture:
A concentrated preparation of live cells that is added to a raw material to initiate fermentation rapidly

2. Starter Cultures References:
Kosikowski, F.V. and V.V. Mistry Cheese and fermented milk foods. Frank Kosikowski, Brooktondale, N. Y.
Chapter 3, Cultures and starters, pp. 26 – 38.
Marth, E.H. and J.L. Steele. (eds.) Applied Dairy Microbiology. Marcel Dekker, Inc., New York, NY.
Chapter 6, Starter cultures and their use. pp

3. Criteria for strain selection
Product
Flavor and texture
Acid production rate
Reliability – ex. bacteriophage resistance

4. Classification of Dairy Starter Cultures
Based on …..
Growth temperature
Number of strains in culture
Culture preservation method
Inoculation method

5. Classification based on growth temperature Thermophilic vs. mesophilic
Thermophilic dairy starter cultures:
Optimum growth temperature:
92–110 F (33–43 C)
S. thermophilus
Lb. delbrueckii subsp. bulgaricus
Lb. helveticus
Rod and coccus jargon
Yogurt, Italian cheeses, Swiss cheese, others

6. Classification based on growth temperature Thermophilic vs. mesophilic
Mesophilic dairy starter cultures:
Optimum growth temperature:
70–90 F (21–32 C)
Lc. lactis subsp. lactis
Lc. lactis subsp. cremoris
Inhibited at > 104F, 40C
Cheddar, Camembert, others

7. Classification based on growth temperature Thermophilic vs. mesophilic
Mesophilic aromatic dairy starter cultures:
Optimum growth temperature:
70–90 F (21–32 C)
Lc. lactis subsp. lactis biovar. diacetylactis
Leuc. mesenteroides subsp. cremoris
Leuc. lactis
Inhibited at > 104F, 40C
Citrate diacetyl, CO2, acetate
Buttermilk, sour cream, cottage cheese, other cheeses (depending on flavor desired)

8. Classification based on # of strains
Single strain culture: One well-characterized strain
Multiple strain culture: A defined mixture of several well-characterized strains
Mixed strain culture: An undefined mixture of unknown or poorly characterized strains

9. Classification based on preservation method
The starter culture manufacturer propagates culture and preserves it in one of several forms….
Liquid
Freeze-dried
Concentrated, freeze-dried
Concentrated, frozen
Form purchased by food manufacture depends on inoculation method….later

10. Large-scale production and preservation of
L.A.B. starter cultures
Standarization to a specific cfu/ml
Concentration
(centrifugation or ultrafiltration)
Liquid starter
culture
(~108 cfu/ml)
Quick-freeze
Freeze-dry
Freeze-dry
Frozen, concentrated starter culture
(~ cfu/g)
Freeze-dried, concentrated starter culture
(~ cfu/g)
Freeze-dried starter culture
(~ cfu/g)

11. Frozen L.A.B. starter cultures
Pellet form
Solid block

12. Classification based on inoculation method
Bulk starter: requires preparation at the dairy plant
Direct Vat Set: does not require preparation at the dairy plant

13. Direct Vat Set Cultures
Concentrated freeze-dried or concentrated frozen
Procedure:
Select culture
Purchase from culture manufacturer
Store in freezer
Use to inoculate fermentation vessel directly

14. Cultures for bulk starter preparation
Freeze-dried, frozen or liquid
Procedure:
Select culture
Purchase from culture manufacturer or get from company stock
Store in freezer or refrigerator
Propagate mother culture, intermediate cultures and bulk starter culture regularly
Use bulk starter to inoculate fermentation vessel

15. Bulk starter preparation: Mother Culture
Small volume culture propagated daily - aseptically
Original inoculum from culture manufacturer or company’s own stock culture
Used to inoculate the first intermediate culture.
Freeze-dried
Culture
Day 1
Day 2
Day 3
Day 4
Day 5…..
3-4 weeks then start over ……
~1L
~10 L
First intermediate culture

16. Starter culture propagation in the dairy
DVS
500 – 1,000 L
DVS

17. Bulk starter growth medium

18. Preparing the bulk starter medium and inoculation
Mother, intermediate and bulk starter cultures should be propagated in a room separate from production facility with positive air pressure and minimal traffic.

19. Traditional (Conventional) Bulk Starter
Bulk Starter: Traditional vs. pH-controlled
Traditional (Conventional) Bulk Starter
No pH control
As pH decreases, cell growth slows and eventually stops
Bulk starter tank is cooled when pH reaches 4.8 – 5.0 (mesophilic) or 4.2 – 4.6 (thermophilic)

20. pH-Controlled Bulk Starter
Bulk Starter: Traditional vs. pH-controlled
pH-Controlled Bulk Starter
2-3X more active than traditional
External pH control
pH is controlled by an automatic pH meter/controller
Keeps pH at a preset level
(mesophilic)
(S. thermophilus)
4.7 (Lb. helveticus, Lb. delbrueckii)
thermophilic
Internal pH control
A buffer is added that is insoluble at neutral pH
As the pH of the medium decreases, the solubility of the buffer increases and slows further pH reduction
Mesophilic cultures only

21. Bulk starter activity
The activity of the bulk starter is evaluated to determine how much to add to the fermentation
Tests are usually based on acid production rate.
Specific test requirements depend on product being made.

22. Commercial Culture Examples

23. Examples:

24. Advantages and disadvantages
Direct Vat Set System
Bulk Starter System

25. Starter Cultures Thermophilic or mesophilic
Single, multiple or mixed strain
Liquid, freeze-dried, concentrated, freeze-dried, or concentrated frozen
Direct-vat-set or bulk starter (traditional or pH-controlled)