Dried Milk | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

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Introduction to Dehydration and Drying

• Dehydration, a simple preservation method, converts surplus milk into dried powders with low moisture content to prevent bacterial growth and quality deterioration.
• Dried milk and milk products can be reconstituted during lean seasons to supplement milk supplies.
• Production of dried milk has become crucial in the Dairy Industry, with significant contributions from entities like the European Economic Community.

Importance of Drying Milk Products

• Dried milk extends shelf life, reduces storage needs, and lowers shipping costs.
• Non-fat dry milk is produced more than whole milk powder due to superior keeping quality.

Role of Skim Milk Powder (SMP)

• SMP is vital in producing Toned Milk, a popular variant in India.
• It helps manage excess milk during surplus periods and supports market milk production during lean seasons.

Purposes of Drying

• Preserves surplus milk for later use when supplies are limited.
• Reduces water content by 87%, making transportation and storage easier.

Legal Standards for Milk Powders

• Whole Milk Powder (WMP):
  • Derived from cow or buffalo milk by water removal, must meet specific standards regarding moisture, fat content, acidity, and microbial counts.
  • Additives like calcium chloride and citric acid are allowed within defined limits.
• Skim Milk Powder (SMP):
  • Produced from skim milk with permitted additives, meeting similar quality standards as WMP.
  • Regulations ensure quality and labeling requirements for consumer transparency.

Summary of Dried Milk Standards and Manufacturing Processes

Standard Specifications for Dried Milk

• Skim Milk Powder Characteristics:
  • Moisture content should not exceed 5.0%.
  • Total milk solids should be at least 95.0%.
  • Solubility Index: 15.0 ml for roller dried, 2.0 ml for spray dried.
  • Fat content should be 9.3%.
  • Total ash on a dry basis should not exceed 1.5%.
  • Titratable acidity should not exceed 1.5% lactic acid.
  • Bacterial count per gram should be less than 50,000, while the coliform count should be under 90/g.
• Whole Milk Powder Characteristics:
  • Moisture content should be maximum 4.0%.
  • Total milk solids should be 96.0%.
  • Solubility Index: 15.0 ml for roller dried, 2.0 ml for spray dried.
  • Fat content should be 7.3%.
  • Total ash on a dry basis should not exceed 1.2%.
  • Titratable acidity should not exceed 26.
  • Bacterial count per gram should be under 50,000, while the coliform count should be less than 90/g.

Composition of Dried Milk

• Whole Milk Powder Composition:
  • Fat: 27.5%
  • Protein: 26.4%
  • Lactose: 26.4%
  • Ash: 5.9%
• Skim Milk Powder Composition:
  • Fat: 08%
  • Protein: 35.9%
  • Lactose: 38.2%
  • Ash: 8.0%

Manufacturing Processes

• Roller Drying Process:
  • Thin film of milk heated for 2 to 3 seconds on a metal surface at 290-300°F.
  • Dried milk continuously scraped off by a stationary knife.
• Spray Drying Process:
  • Milk atomized into fine droplets and dried quickly by hot air.
  • Resulting powder collected from the air stream.

These standards ensure quality and safety in the production of dried milks, meeting specific criteria for moisture content, fat percentage, solubility, and bacterial limits.

Industrial Milk Drying Processes

Industrial processes for drying milk involve roller drying and spray drying methods.

Roller Drying Method

• Consists of two steam-heated cylinders with a small gap where milk is fed.
• The milk film is dried on the drum's surface between feeding and scraping.
• The rate of evaporation is determined by steam pressure in the drum.
• Rolls rotate towards each other, drying the milk film, which is then scraped off.

Drying Process

• Milk film is spread over hot surfaces, dried, and scraped off by knives.
• Uniform film thickness is crucial for maintaining product quality.

Quality Concerns

• Quality of raw milk impacts powder quality.
• Acidic milk leads to darker powder with poor flavor.

Properties of Roller Dried Powder

• Majority of bacteria are destroyed through heat treatment.
• Pathogenic species are absent in roller dried powder.

Disadvantages of Roller Dried Powder

• Has a cooked flavor.
• Reconstituted powder has poor solubility and appearance.
• Fat globule structure is damaged, giving a slightly oily appearance.

Spray Drying Process

• Milk is sprayed through hot air, forming tiny soluble spheres.
• Manufacturing involves steps like milk reception, standardization, clarification, homogenization, and pre-heating.

Manufacturing Details

• High-grade raw milk is crucial for the process.
• Milk is standardized to meet compositional standards.
• Clarification improves keeping quality by removing certain compounds.
• Homogenization ensures uniform fat distribution in the final product.
• Pre-heating destroys bacteria and inactivates enzymes, aiding in production.

Summary of Milk Powder Production Process

Effect of Temperature on O/R Potential

• Heating milk to a certain temperature causes a decrease in O/R potential due to the release of sulphydryl compounds.
• Preheating leads to the production of a spray powder that remains palatable even after long-term storage.
• Cooked flavor may develop due to heat, but it is not usually considered undesirable.

Condensing or Preconcentration

• Dried milk from precondensed fresh milk has better shelf life compared to milk that is not precondensed.
• Condensing under vacuum helps in removing volatile substances and increasing the bulk density of the powder, which is crucial for maintaining quality.

Spray Drying Process

• Spray drying involves atomizing concentrated milk into fine droplets that are dried rapidly in a hot air chamber.
• The dried milk is collected as a powder without the need for grinding.
• The process requires careful temperature control to prevent overheating of the milk.

Packaging and Storage

• Proper packaging is essential for maintaining the quality of milk powder.
• Using inert gas in packaging helps in extending the storage life of milk powder.
• Storage at temperatures below 24°C is recommended for preserving the quality of the product.

Properties of Dried Milk Powder

• Roller dried powder contains free fat due to the production process, while spray dried powder has enclosed air.
• Lactose plays a significant role in forming the structure of dried milk particles.
• Bulk density of milk powder is influenced by various factors like air content and particle structure.

Understanding Milk Powder Quality Assessment

• Characteristics of Milk Powder

  • Heavy powder, characterized by a high concentration of particles, results in a dense, heavy product.
  • Roller powder, on the other hand, is lighter with a bulk density ranging between 0.3 and 0.6 g/ml.
  • Heavy powder typically demonstrates better solubility and wettability compared to roller powder.

• Quality Evaluation of Dried Milk

  • Good quality dried milk should flow smoothly without lumps, exhibit a uniform white or light cream color, and avoid moisture absorption.
  • Proper packaging is crucial as inadequate packaging can lead to severe caking and ruin the quality of the powder.

• Grading Standards

  • The American Dairy Science Association provides a scorecard for both whole milk powder and skim milk powder to assess various parameters like appearance, flavor, and packaging.

• Inspection Process

  • During inspection, random cans or bags are selected for examination, focusing on appearance, rust, color uniformity, and the presence of foreign particles.
  • Quality milk powder should be free from lumps, caking, and foreign matter, ensuring proper storage conditions to maintain its integrity.

• Flavor Assessment and Storage

  • Flavor evaluation involves assessing the smell upon opening, reconstituting the powder, and tasting for quality.
  • Various storage defects like brown discoloration and oxidized taint can impact the flavor and quality of the milk powder.

• Preventive Measures

  • To prevent storage defects like fat oxidation, measures such as packing in inert gas, high-temperature preheating, and addition of antioxidants like ascorbic acid and ethyl gallate are recommended.
  • Stale and undesirable flavors in milk powders can be prevented by maintaining low moisture content and proper storage conditions.

• Laboratory Testing

  • Laboratory tests as per Indian Standard specifications are essential to ensure the quality and safety of milk powder products.

Uses of Milk Powder

• Skim Milk Powder Uses:

  • Skim Milk Powder finds application in various areas such as:
  • Preparation of toned, double toned, and recombined milks
  • Adding to tea and coffee during milk shortages
  • Manufacturing ice cream
  • Production of candy and confectionery
  • Incorporation into prepared foods
  • Use in breads, rolls, and biscuits
  • Utilization in cultured products
  • Key ingredient in the preparation of certain Indian sweets

• A spray dried product is preferred when complete reconstitution is necessary, while a roller dried product is more cost-effective for other uses.

• Whole Milk Powder Uses:

  • Whole Milk Powder is employed for various purposes including:
  • Creating reconstituted milk
  • Adding to tea and coffee
  • Preparing baby food
  • Incorporating into candy, confectionery, and bakery products

• The utilization of Whole Milk Powder is generally lower compared to Skim Milk Powder due to its shorter shelf-life.