Quality Testing and Grading | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Quality Testing and Grading of Raw Milk

• Importance of Quality Testing

  • Every dairy plant should have a well-equipped laboratory for testing raw and processed milk regularly.
  • Regular tests ensure the safety and quality of milk supplied to consumers.

• Receiving Milk

  • Milk is delivered to collection centers or milk plants, where it is graded, measured, and sampled.
  • Milk quality on the receiving platform depends on factors like clean production, prompt cooling, and transport.
  • Milk reception should be expedited to prevent deterioration and ensure freshness.

• Quality Testing Process

  • Organoleptic tests are conducted to assess milk quality based on smell, taste, appearance, acidity, and sediment.
  • Odour test is crucial to determine milk quality, with sourness indicating bacterial contamination.
  • Appearance, temperature, sediment, acidity, and lactometer reading are key factors in assessing milk quality.

• Sampling Importance

  • Securing accurate samples for chemical and bacteriological analysis is crucial for quality assessment.
  • Sterility and cleanliness are vital in obtaining representative samples for testing.

Milk Sampling and Testing Overview

• Sampling Prerequisites

  • Sampling of milk is crucial for obtaining a representative sample.
  • Methods include manual or mechanical mixing in cans or tanks.
  • Quick dumping of milk into a weigh tank is another technique.

• Sample Collection

  • Samples can be individual or composite.
  • Preservatives like mercury chloride are used for composite samples for chemical examination.
  • Sterile containers are necessary for bacteriological examination samples.
  • Samples need to be packed in ice and dispatched to the laboratory promptly.

• Quality Control in the Laboratory

  • Each milk sample is analyzed for fat percentage using Gerber's method.
  • Payment for milk may be based on fat content or total solids.
  • Modern tools like 'Milkotesters' and 'Promilk' are used for fat and protein estimation.

• Grading of Raw Milk

  • Chemical analysis is conducted to measure fat, protein, total solids, and solids-not-fat (SNF).
  • Bacteriological tests are essential for ensuring milk safety.
  • Tests include Dye-reduction test, Direct Microscopic Count, Standard Plate Count, and Coliform Organism examination.

• Bacteriological Tests

  • Dye-Reduction Test

    • This test assesses milk quality based on the reduction of methylene blue dye.
    • Results indicate the presence and activity of bacteria in the sample.
    • It helps in grading milk quality based on reduction time.

  • Direct Microscopic Count

    • This method involves examining stained films of milk under a microscope.
    • It provides rapid estimation of bacterial population and contamination tracing.
    • Useful for classifying raw milk samples and identifying contamination sources.

Quality and Storage Grade of Whole Milk

• Milk Storage and Preservation

  • Milk needs proper storage from production to consumer consumption.
  • Chilling milk to 5°C or lower prevents bacterial deterioration.
  • Chemical preservatives are not allowed in milk under food laws.
  • Insulated tanks and chillers maintain milk quality during transportation.

Grading of Raw Milk

• Standard Plate Count

  • Method for enumerating bacteria in milk samples.
  • Used for assessing quality based on bacterial count.
  • Specific plate count limits for pasteurized and raw milk.

• Examination for Coliform Organisms

  • Presence of coliforms in milk indicates contamination.
  • Coliform testing crucial for assessing milk safety.
  • Effect of pasteurization on coliform organisms.

Designated Milks in England

• Tuberculin Tested Milk

  • Milk tested for tuberculosis, delivered in sealed containers.
  • Specific requirements for different types of tuberculin-tested milk.

• Pasteurized and Sterilized Milk

  • Differentiation between pasteurized and sterilized milk.
  • Testing requirements for ensuring quality and safety.

Special Conditions for Grant of Licences

• Taberculin Tested Milk for IAS(M)
• Special conditions include milk from an attested herd.
• Animals must undergo Tuberculosis test every 6 months with removal of reactors.
• No inoculation against T.B. or Brucella abortus vaccines in the herd.
• All animals should be marked for proper identification.
• Milk must pass Coliform and MBR Tests if unpasteurized.

Designated Milk in America (U.S.A)

• American Association of Medical Milk Commission regulates milk grades.
• Three main grades in America: Certified, Grade A Raw, and Pasteurized Milk.
• Certified Milk:
  • Controlled by American Association of Medical Milk Commission.
  • Tuberculosis and Brucellosis tests conducted regularly.
  • Healthy herd and milk handlers with specific milk production standards.
• Grade A Raw Milk:
  • Less oversight compared to Certified Milk.
  • Dependent on the integrity of producers for safety.
  • Higher bacterial count range.
• Pasteurized Milk:
  • Must meet U.S. Public Health Service regulations.
  • Specific pasteurization temperatures and bacterial count limits.

Designated Milk in India

• No graded market milk in India based on quality.
• Various types of milk including cow, buffalo, mixed, pasteurized, standardized, and toned.
• Standards for fat and SNF to detect adulteration.

Skimmed Milk

• Skim milk is the by-product of cream separation.
• Contains all nutrients except fat and fat-soluble vitamins.
• Used in various dairy products and plays a crucial role in dairy development programs.
• Legal standards for skim milk under P.F.A. Rules 1955 in India.

The Composition and Types of Cream

• Cream Overview: Cream is a dairy product that contains a significant amount of milk fat, ranging from 18 to 25 percent. It consists of water, fat, proteins, lactose, and ash, with the fat content influencing the solids-not-fat ratio.
• Types of Cream:
  • Table cream
  • Light cream
  • Coffee cream
  • Whipped cream
  • Heavy cream
  • Plastic cream
• Chemical Composition: Thin cream and thick cream have varying compositions based on fat content. Higher fat percentages in cream result in lower solids-not-fat content.

Understanding Cream's Nutritive Value and Separation Process

• Nutritive Value: Cream is rich in energy-giving fat and fat-soluble vitamins like A, D, E, and K. The separation of cream from skim milk is facilitated by the differing densities of milk fat and skim milk.
• Fat Globules and Cream Rise: Factors such as the size of fat globules, temperature, and clumping impact the rate at which cream rises. Larger fat globules, lower temperatures, and increased clumping enhance the cream separation process.
• Cream Separation Methods:
  • Gravity Method: Cream rises due to varying densities of fat and skim milk.
  • Centrifugal Separation: Involves centrifugal force to separate cream efficiently.

Centrifugal Cream Separator Operation

• Separator Assembly: Components are dismantled for cleaning daily and reassembled for operation.
• Separator Function: The bowl rotates at high speed, separating cream from milk through centrifugal force.
• Cleaning Process: Hot water sanitizes the separator before milk is passed through for separation.

Modern Cream Separator Structure

• Parts: Components include a supply can, regulating float, cream cover, skim milk cover, skimming discs, and more.
• Operation: Milk enters from the bottom, distributes into separating discs, and centrifugal force separates cream efficiently.
• Cream Separator Operation
  • Cream Separation Process: In a cream separator, skim milk and cream are separated by their different densities. Skim milk forms a layer on the periphery of the bowl, while cream recedes to the center. They are then forced out through separate outlets.
  • Regulation of Cream Fat Content: The percentage of fat in the cream can be adjusted by manipulating the cream screw, allowing for control over the fat content of the separated cream.
  • Airtight Separators for Large-Scale Handling: In large dairies and creameries, airtight separators are preferred to open-type bowls to avoid excessive foam in skim milk during processing, ensuring more precise separation.
• Cream Separator Components
  • Main Components: The bowl shell, bowl nut, cream disc, bowl ring, cream-skim milk interface (IAS(M)), distributor, and skimming discs are essential parts in a cream separator.
  • Sectional View: A sectional view of the cream separator bowl illustrates the flow of milk, cream, and skim milk through the separator, showing the separation process clearly.
• Efficiency of Cream Separation
  • Definition of Efficiency: The efficiency of a cream separator refers to the percentage of total fat from milk recovered in the cream. An efficient separator can recover 98 to 99.5% of the butterfat in the milk.
  • Factors Affecting Efficiency:
    • Temperature: The temperature of the milk should be above the fat melting point for efficient separation (around 40°C).
    • Separator Speed: Optimum speed is crucial for effective separation, balancing fat content in skim milk.
    • Mechanical Condition: Smooth machine operation is essential for high skimming efficiency.
    • Cleanliness: Accumulated skim affects fat loss in skim milk.
• Ideal Cream Characteristics
  • Richness for Churning: Cream with 33% fat is ideal for churning, with a fat test between 35 to 45% recommended for creamery use.
  • Influence of Milk Richness: The fat percentage in cream directly correlates with the fat content in milk.
  • Speed Impact: Higher bowl speed results in cream with higher fat content.

Processing of Cream

• Neutralization of cream:
  • Neutralization involves adjusting the acidity of cream between 0.1 and 0.3 per cent lactic acid by adding an alkali. This process helps in pasteurizing cream without losing fat due to coagulation of casein, which occurs in highly acidic cream. It also prevents curd formation in butter and enhances its shelf life.
• Standardization of cream:
  • Standardization refers to adjusting the fat content in cream to meet specific requirements. This is achieved by adding calculated amounts of skim milk to reach the desired fat percentage.
• Pasteurization of cream:
  • Pasteurization involves heating each part of the cream to at least 71°C (160°F) and maintaining this temperature for a minimum of 20 minutes. This process aims to destroy harmful microorganisms, extend the shelf life of cream and butter, complete the neutralization process, eliminate gas-forming substances, and reduce off-flavors.

Requirements of High-Grade Table Cream

• Flavor and Quality:
  • High-quality table cream should possess a clean, sweet, and nutty flavor. Its texture should be smooth, uniform, and appropriately viscous for the fat content present. Additionally, the cream should have a visually appealing appearance.

Classification of Cream Grades

• Special or Sweet Cream Grade:
  • Cream scoring 92 and above with acidity below 0.2% lactic acid.
• First Grade:
  • Cream scoring 90-91 with a clean flavor and acidity below 0.6% lactic acid.
• Second Grade:
  • Cream scoring 88-89 with acidity above 0.6% lactic acid and some objectionable flavors, but free from strong odors.
• Weed-Flavored Cream:
  • Cream scoring 83 with flavors reminiscent of unpleasant weeds.
• Illegal or Unlawful Cream:
  • Cream scoring 81 or lower with flavors like gasoline or kerosene, deemed unsuitable for butter production.

Different Methods of Pasteurization

• Holder Pasteurization: This method involves heating cream in a batch/holder pasteurizer to 71°C (160°F) for 20 minutes and then cooling it. It is suitable for small-scale processing.
• HTST (Plate) Pasteurization: A continuous process designed for large-scale operations. It allows for better regeneration and is capable of heating cream to 95-100°C (203-212°F) for 15 to 16 seconds using a plate pasteurizer.
• Vacuum Pasteurization (Vacreation): Another continuous process involving dilution of initial cream where the fat content may be reduced by 6 to 8 percent.

Manufacture of Different Types of Cream

• Sterilized or Canned Cream: Steps include standardizing fresh cream to 20% fat, pre-heating, homogenizing, cooling, filling into cans, and sterilizing in batch sterilizers.
• Plastic Cream: Produced by re-separating normal cream, pasteurizing, and cooling before separation. It has high butterfat content and is commonly used in ice-cream production.
• Frozen Cream: Freezing cream improves its shelf life during transportation and storage. It is primarily used by ice-cream manufacturers to prevent 'oiling-off' after thawing.
• Clotted Cream: Prepared by heating milk and collecting the clotted cream layer that forms on the surface after cooling slowly.
• Sour Cream: A high-acidity cream made by fermenting pasteurized and homogenized cream with lactic acid bacteria.
• Synthetic Cream: Created by emulsifying margarine into milk or reconstituted liquids to mimic cream's properties.

Packaging, Storage, and Distribution of Cream

• Packaging: Cream is packaged in various containers like glass bottles, paper cartons, LDPE sachets, and plastic bottles for retail sale.
• Storage and Distribution: Cream should be stored at 5-10°C (41-50°F) and distributed promptly, preferably within 3 hours of removal from cold storage.

Defects in Cream, Causes, and Prevention

• Common Defects: Defects in cream can result from low-quality milk and faulty processing methods.

Table Cream Defects

• Flavor Cooked: Caused by excessive heating during pasteurization.
• Prevention: Proper heating procedures during pasteurization can help prevent this issue.

Note: A cooked flavor, while undesirable, can indicate good keeping quality.

Namo of Defect: Feed and Weed

• Highly acid/sour
• Causes:
  • Feeding of milk tainting weeds within 3 hours before milking
  • Using sour milk for separation
• Prevention:
  • Feeding of milk tainting feeds and weeds soon after milking
  • Eradication of milk tainting weeds
  • Vacuum pasteurization of cream
  • Using fresh, sweet milk for preparation

Examples and Explanation:

The defect "Feed and Weed" is characterized by a highly acidic or sour taste in milk. This defect occurs when cows consume milk-tainting weeds within three hours before milking. Additionally, using sour milk for separation can also lead to this issue.

To prevent this defect, it is essential to feed cows with milk-tainting feeds and weeds immediately after milking. Furthermore, eliminating milk-tainting weeds from the environment is crucial. Vacuum pasteurization of cream and using fresh, sweet milk for preparation can help in avoiding this problem.

Implications and Impact:

The presence of the "Feed and Weed" defect can significantly affect the quality and taste of dairy products. Consumers may perceive the milk as undesirable due to its sourness, potentially leading to decreased sales and reputation damage for dairy producers.