Sampling of Milk and Milk Products

By Skumar -

 

Sampling of Milk and Milk Products


Introduction

Milk is a highly perishable and heterogeneous biological fluid. Accurate evaluation of milk quality depends largely on proper sampling, rapid platform tests, and standard chemical analysis. Errors in sampling or testing may lead to incorrect conclusions regarding milk quality, payment, and suitability for processing.

Sampling of Milk and Milk Products

Meaning of Sampling

Sampling is the process of collecting a small representative portion of milk or milk product that truly reflects the characteristics of the whole lot.

Objectives of Milk Sampling

  • To assess quality and composition of milk

  • To detect adulteration

  • To ensure fair payment based on fat and SNF

  • To evaluate processing suitability

Principles of Good Sampling

  • Milk must be thoroughly mixed before sampling

  • Sampling equipment should be clean and dry

  • Sample should be representative of the entire lot

  • Sampling should be done quickly and hygienically

  • Sample containers must be properly labeled

Sampling of Milk Products

  • Solid and semi-solid products should be uniformly mixed

  • Samples should be collected from different locations of the lot

  • Air-tight containers should be used to avoid contamination

Platform Tests of Milk

Meaning

Platform tests are rapid tests conducted at milk reception platforms to quickly assess milk quality before acceptance or rejection.

Objectives of Platform Tests

  • Rapid quality evaluation

  • Detection of abnormal or adulterated milk

  • Prevention of spoilage during processing

Common Platform Tests

1. Organoleptic Test

  • Based on colour, taste, smell, and appearance

  • Detects sour, bitter, or off-flavoured milk

2. Clot on Boiling (COB) Test

  • Milk is boiled to check coagulation

  • Positive test indicates high acidity or sour milk

3. Alcohol Test

  • Equal quantity of milk and alcohol mixed

  • Coagulation indicates poor heat stability

4. Acidity Test (Quick estimation)

  • Indicates freshness of milk

Determination of Fat by Gerber’s Method

Principle

Milk fat is separated by digesting proteins with sulphuric acid and centrifuging with iso-amyl alcohol. Fat is measured directly in a butyrometer.

Apparatus and Chemicals

  • Gerber butyrometer

  • Sulphuric acid (specific gravity 1.82)

  • Iso-amyl alcohol

  • Gerber centrifuge

  • Water bath

Procedure

  1. Add sulphuric acid to butyrometer

  2. Add measured quantity of milk

  3. Add iso-amyl alcohol

  4. Centrifuge the mixture

  5. Keep in water bath at 65°C

  6. Read fat percentage directly

Significance

  • Rapid and accurate

  • Widely used for payment of milk

  • Standard method in dairy industry

Determination of SNF, Total Solids and Specific Gravity

Specific Gravity of Milk

  • Determined using a lactometer

  • Normal milk specific gravity: 1.028–1.034

Total Solids (TS)

  • TS = Fat + SNF

  • Represents total nutrients present in milk

Solids-Not-Fat (SNF)

  • SNF includes lactose, proteins, minerals

  • Calculated using formula:

SNF (%) = (CLR ÷ 4) + (0.25 × Fat %) + 0.44

(CLR = Corrected Lactometer Reading)

Importance

  • Detects adulteration with water

  • Ensures compliance with legal standards

  • Important for product yield calculations

Determination of Acidity of Milk

Meaning

Acidity of milk indicates the degree of freshness and is expressed as percentage lactic acid.

Principle

Milk acidity is determined by titration with standard NaOH using phenolphthalein indicator.

Procedure

  1. Take measured quantity of milk

  2. Add phenolphthalein indicator

  3. Titrate with NaOH until faint pink colour appears

  4. Calculate acidity

Normal Acidity of Milk

  • Fresh milk: 0.13–0.17% lactic acid

Importance

  • Indicates milk freshness

  • Helps detect sour milk

  • Important for heat processing suitability

Importance of Milk Testing in Dairy Industry

  • Ensures quality and safety

  • Prevents economic losses

  • Protects consumer health

  • Supports fair pricing system

  • Maintains processing efficiency

Conclusion

Sampling, platform testing, and chemical analysis of milk are essential components of dairy quality control. Proper sampling ensures representative results, while platform tests help in rapid screening of milk at reception points. Laboratory methods such as Gerber’s fat test, determination of SNF, total solids, specific gravity, and acidity provide precise information about milk composition and freshness.

MCQs: Milk Sampling, Platform Tests & Chemical Analysis

1. The main objective of milk sampling is to:

A. Increase milk shelf life
B. Get a representative portion of milk
C. Improve milk colour
D. Reduce acidity

✅ Answer: B
Explanation: Proper sampling ensures the sample truly represents the entire lot.

2. Before sampling milk, it should be:

A. Heated
B. Filtered
C. Thoroughly mixed
D. Cooled

✅ Answer: C
Explanation: Fat rises to the top; mixing ensures uniform distribution.

3. Which instrument is commonly used for milk sampling?

A. Pipette
B. Dip sampler
C. Lactometer
D. Burette

✅ Answer: B
Explanation: Dip sampler is designed for hygienic milk sampling.

4. Platform tests are conducted to:

A. Determine fat content
B. Evaluate microbial count
C. Quickly accept or reject milk
D. Determine SNF

✅ Answer: C
Explanation: Platform tests are rapid screening tests.

5. Which is NOT a platform test?

A. COB test
B. Alcohol test
C. Gerber test
D. Organoleptic test

✅ Answer: C
Explanation: Gerber test is a laboratory fat test.

6. The Clot on Boiling (COB) test detects:

A. Fat content
B. Adulteration
C. High acidity
D. SNF

✅ Answer: C
Explanation: Milk with high acidity clots on boiling.

7. Positive COB test indicates:

A. Fresh milk
B. Heat-stable milk
C. Sour milk
D. Adulterated milk

✅ Answer: C
Explanation: Acidic milk coagulates on boiling.

8. Alcohol test is used to check:

A. Milk freshness
B. Heat stability
C. Fat content
D. Specific gravity

✅ Answer: B
Explanation: Alcohol destabilizes proteins in poor quality milk.

9. Gerber method is used for determination of:

A. SNF
B. Acidity
C. Fat
D. TS

✅ Answer: C
Explanation: Gerber method directly measures milk fat.

10. In Gerber method, sulphuric acid is used to:

A. Separate fat
B. Dissolve fat
C. Digest proteins
D. Increase acidity

✅ Answer: C
Explanation: Acid digests proteins and releases fat.

11. Iso-amyl alcohol in Gerber method helps to:

A. Increase fat
B. Improve fat separation
C. Reduce acidity
D. Digest lactose

✅ Answer: B
Explanation: It prevents charring and sharpens fat column.

12. The fat percentage in Gerber method is read from:

A. Lactometer
B. Burette
C. Butyrometer
D. Pipette

✅ Answer: C
Explanation: Butyrometer has calibrated fat scale.

13. Gerber test reading is taken at:

A. Room temperature
B. 37°C
C. 65°C
D. 100°C

✅ Answer: C
Explanation: Fat expands uniformly at 65°C.

14. Specific gravity of milk is measured by:

A. Hydrometer
B. Thermometer
C. Lactometer
D. pH meter

✅ Answer: C
Explanation: Lactometer measures milk density.

15. Normal specific gravity of milk ranges between:

A. 1.010–1.020
B. 1.028–1.034
C. 1.040–1.050
D. 1.060–1.070

✅ Answer: B
Explanation: This is the normal range for genuine milk.

16. Addition of water to milk will:

A. Increase specific gravity
B. Decrease specific gravity
C. Increase fat
D. Increase SNF

✅ Answer: B
Explanation: Water lowers milk density.

17. SNF in milk includes:

A. Fat and protein
B. Lactose, protein, minerals
C. Fat only
D. Water only

✅ Answer: B
Explanation: SNF excludes fat and water.

18. Total solids in milk are equal to:

A. Fat + water
B. SNF + water
C. Fat + SNF
D. Protein + lactose

✅ Answer: C
Explanation: TS = Fat + SNF.

19. SNF percentage is calculated using:

A. pH value
B. Lactometer reading
C. Gerber reading
D. Acidity

✅ Answer: B
Explanation: SNF is calculated from CLR and fat %.

20. CLR stands for:

A. Corrected Lactose Reading
B. Corrected Lactometer Reading
C. Calculated Lactometer Ratio
D. Constant Lactometer Reading

✅ Answer: B
Explanation: CLR accounts for temperature correction.

21. Acidity of milk is expressed as:

A. % citric acid
B. % lactic acid
C. pH units
D. mg acid

✅ Answer: B
Explanation: Milk acidity is expressed as lactic acid %.

22. Normal acidity of fresh milk is:

A. 0.05–0.10%
B. 0.13–0.17%
C. 0.20–0.25%
D. 0.30–0.35%

✅ Answer: B
Explanation: This is normal titratable acidity.

23. Acidity of milk increases due to:

A. Fat breakdown
B. Protein breakdown
C. Lactose fermentation
D. Mineral loss

✅ Answer: C
Explanation: Lactic acid bacteria ferment lactose.

24. Indicator used in acidity determination is:

A. Methyl orange
B. Litmus
C. Phenolphthalein
D. Bromothymol blue

✅ Answer: C
Explanation: Phenolphthalein gives faint pink endpoint.

25. Milk showing acidity above 0.17% is considered:

A. Fresh
B. Neutral
C. Sour
D. Alkaline

✅ Answer: C
Explanation: High acidity indicates souring.

26. Which test gives quickest assessment of milk quality?

A. SPC
B. Gerber test
C. MBRT
D. Acidity test

✅ Answer: C
Explanation: MBRT is a rapid dye reduction test.

27. MBRT measures:

A. Fat
B. Acidity
C. Microbial activity
D. SNF

✅ Answer: C
Explanation: Faster reduction = higher bacteria.

28. Longer MBRT time indicates:

A. Poor quality milk
B. High acidity
C. Good quality milk
D. Adulterated milk

✅ Answer: C
Explanation: Less bacteria take longer to reduce dye.

29. Resazurin test is a:

A. Chemical test
B. Physical test
C. Dye reduction test
D. Fat test

✅ Answer: C
Explanation: It indicates microbial load by colour change.

30. Psychrotrophic bacteria grow best at:

A. High temperature
B. Room temperature
C. Refrigeration temperature
D. Boiling temperature

✅ Answer: C
Explanation: They grow at low temperatures.

31. Which microorganism dominates chilled milk spoilage?

A. Lactobacillus
B. Pseudomonas
C. E. coli
D. Streptococcus

✅ Answer: B
Explanation: Pseudomonas is psychrotrophic.

32. Milk sampling container should be:

A. Wet
B. Dirty
C. Sterile and dry
D. Plastic only

✅ Answer: C
Explanation: Prevents contamination.

33. Poor sampling mainly affects:

A. Milk colour
B. Test accuracy
C. Fat content
D. Acidity

✅ Answer: B
Explanation: Incorrect sample gives wrong results.

34. Which test checks sensory quality of milk?

A. Alcohol test
B. COB test
C. Organoleptic test
D. MBRT

✅ Answer: C
Explanation: Based on smell, taste, appearance.

35. Sour smell in milk is due to:

A. Fat oxidation
B. Protein breakdown
C. Lactic acid formation
D. Mineral loss

✅ Answer: C

36. SNF decreases mainly due to:

A. Cream removal
B. Heating
C. Water adulteration
D. Storage

✅ Answer: C

37. Which component affects milk density most?

A. Fat
B. Water
C. Minerals
D. Vitamins

✅ Answer: A
Explanation: Fat lowers density.

38. Milk with low fat will show:

A. Higher specific gravity
B. Lower specific gravity
C. No change
D. Zero density

✅ Answer: A

39. Gerber method is preferred because it is:

A. Expensive
B. Time consuming
C. Rapid and accurate
D. Complex

✅ Answer: C

40. Butyrometer is graduated in:

A. ml
B. g
C. % fat
D. °C

✅ Answer: C

41. Milk acidity test is a type of:

A. Physical test
B. Biological test
C. Chemical test
D. Sensory test

✅ Answer: C

42. Milk becomes unsuitable for pasteurization when:

A. Fat is low
B. Acidity is high
C. SNF is high
D. Density is normal

✅ Answer: B

43. Which factor does NOT affect milk acidity?

A. Storage temperature
B. Bacterial activity
C. Lactose content
D. Fat percentage

✅ Answer: D

44. Sampling error mainly occurs due to:

A. Improper mixing
B. High fat
C. Low SNF
D. Pasteurization

✅ Answer: A

45. Which test directly measures fat?

A. Lactometer test
B. Acidity test
C. Gerber test
D. Alcohol test

✅ Answer: C

46. Specific gravity correction is needed because of:

A. Fat variation
B. Temperature variation
C. Acidity
D. SNF

✅ Answer: B

47. Milk showing coagulation in alcohol test indicates:

A. Fresh milk
B. Heat stable milk
C. Poor quality milk
D. Adulterated milk

✅ Answer: C

48. Platform tests are mainly carried out at:

A. Laboratory
B. Farm
C. Milk reception dock
D. Retail shop

✅ Answer: C

49. High acidity milk is rejected because it:

A. Has more fat
B. Curds during heating
C. Has high SNF
D. Is sweet

✅ Answer: B

50. Correct milk analysis ensures:

A. Consumer safety and fair payment
B. Increase milk price
C. Increase fat
D. Reduce testing

✅ Answer: A



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