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

Drying and Preservation of Perishable Foods

• Dehydration, also known as drying, is a straightforward method used to preserve perishable foods.
• It involves converting surplus milk and milk products into dried powders with low moisture content.
• The purpose is to inhibit bacterial growth and prevent quality deterioration.

Significance of Dried Milk and Milk Products

• Dried milk and milk products can be reconstituted to supplement milk shortages, especially during lean seasons.
• Various milk products such as cream, cheese, dahi, and by-products like whey can be dried to prolong shelf life.
• This process has become a crucial segment of the Dairy Industry.

Contributions and Initiatives

• The European Economic Community (EEC) contributed significantly to India's dairy industry.
• Operations like "Operation Flood Stage I" and "Operation Flood Stage II" aimed to bolster dairy production in India.
• India has shown remarkable progress in milk drying capacity and production over the years.

Global Perspective

• India's production of skim milk powder (SMP) has been notable on a global scale.
• By the year 1995, India's milk drying capacity had substantially increased, allowing for even export to other countries.

Summary: Milk Drying Capacity and Production

• Despite an increase in milk drying capacity, exports have not significantly risen since dried milk is used locally to fulfill demand during lean seasons.
• Future production of dried milk and milk products is expected to rise due to factors such as better keeping quality, requiring less storage space, and lower shipping costs.
• Non-fat dry milk production surpasses whole milk powder production primarily because of its superior keeping quality.
• Toned Milk and SMP:
  • Dry milk, particularly Skimmed Milk Powder (SMP), is crucial for producing Toned Milk, which has established itself in the Indian market.
  • Dry milk serves as a valuable resource during surplus milk periods, allowing dairy factories to manage excess supply and redirect it to market milk through Toned Milk production.
  • Dry milk essentially acts as a stabilizing force in the dairy industry, balancing milk supply and demand effectively.
• Historical Context:
  • The first commercial production of spray-dried milk in India commenced in 1955 at AMUL Dairy, Anand.

Purpose of Drying

• This process aims to preserve excess milk during abundant periods for later use when supply is low.
• By removing 87% of water, the milk is condensed for easier storage and transportation.
• Dried milk prevents microbiological growth but may undergo gradual chemical changes over time.

Legal Standards for Whole Milk Powder (WMP)

• Whole Milk Powder is derived from cow or buffalo milk by water removal, following PFA Rules (1984).
• It must contain specific additives within defined limits and meet requirements for moisture, fat content, acidity, and microbial counts.
• Labeling should declare the drying process, and packaging regulations apply for certain quantities.

Legal Standards for Skim Milk Powder (SMP)

• Skim Milk Powder is produced from skim milk, adhering to PFA Rules (1984) regarding additives and composition.
• It has restrictions on fat content, moisture levels, acidity, and microbial counts, with similar packaging requirements as WMP.

Indian Standards for Dried Milks

• Indian Standards Institution sets specifications for dried milks, including moisture, milk solids, solubility, fat content, and microbial limits.
• Specific values for parameters like titratable acidity and bacterial counts are outlined.

Composition of Dried Milks

• An average percentage composition of Whole Milk Powder and Skim Milk Powder is provided, detailing moisture, fat, protein, lactose, and ash content.
• Values are based on data from the book "Drying of Milk and Milk Products" by Hall and Hedrick (1971).

Food and Nutritive Value

• The nutritional content of milk powder is similar to that of the milk it is derived from.
• During spray-drying, there is a slight loss of lysine, while roller drying's high heat destroys more lysine.
• Dry whole milk is rich in vitamin A, calcium, and phosphorus.
• It is also a valuable source of riboflavin.

Details of Manufacture

• Various drying methods exist, including freeze-drying through processes like freezing out water and centrifuging, and freezing milk followed by sublimation.
• The two most common and widely accepted drying methods involve the application of heat.

Roller Drying Process

• This process, also known as Film or Drum Drying, involves heating a thin film of milk at atmospheric pressure on a steam-heated metal surface at around 290-300°F (143-149°C) for 2 to 3 seconds.
• The dried milk film is continuously removed by a stationary knife opposite to where the milk is applied.
• The drum dryer can be a single drying drum, double drying drums, or a combination of a single drying drum and a film-applying drum.

A Common Design of Milk Drying Equipment

• Overview of the Design

  • Consists of two horizontally mounted steam-heated cylinders with a small gap between them.
  • Rolls are typically made of cast iron or stainless steel, accurately ground for smoothness.

• Drying Process

  • Milk film travels on the drum between feed and scraper, with drying occurring over about three-quarters of a drum revolution.
  • Drying rate is controlled by steam pressure in the drum.

• Operational Details

  • Rolls rotate towards each other at a specific speed, mounted in a sturdy framework to minimize vibration.
  • Steam at a controlled pressure is supplied to the rolls.
  • Milk spreads as a thin film over the hot surfaces, gets dried, and is then removed by scraper knives.
  • Scraper knives are crucial for removing the dried milk film efficiently.

• Importance of Film Thickness

  • Uniform film thickness is vital for consistent drying and moisture content.
  • Uniform moisture content ensures better solubility, flavor, and color of the final product.

Manufacturing Processes of Milk Powder

• Roller Drying Process

  • The milk film does not reach the temperature of the rolls due to rapid water evaporation.
  • Steam consumption is 1.15 kg per litre during the process.
  • Quality heavily relies on skill to prevent incomplete drying or excessive heat exposure.
  • The quality of raw milk directly impacts the powder quality.

• Properties of Roller-Dried Powder

  • Heat treatment eliminates most bacteria, making the powder pathogen-free.

• Disadvantages of Roller-Dried Powder

  • Distinct cooked flavor.
  • Unattractive appearance when reconstituted.
  • Poor solubility (around 85%), leading to obvious insoluble sediment.
  • Damaged fat globule structure, resulting in an oily appearance which can be mitigated by homogenization before drying.

• Spray Drying Process

  • Milk is sprayed into hot air, forming tiny spheres that are highly soluble.

• Manufacturing Details of Spray Drying

  • Receiving Milk

    • Only high-quality raw milk should be used, free from lipolytic changes, acidity below 0.15%, and copper contamination.

  • Standardization

    • Milk is adjusted to the required fat and SNF ratio to meet compositional standards and legal requirements.

  • Clarification

    • Enhances the keeping quality of whole milk powder by removing lecithin and other oxidants that slow down fat oxidation.

  • Homogenization

    • Pre-heating the milk to 71°C/160°F before filtration aids in uniform fat distribution in the final product.
    • Homogenization is done at 2500 psi in the first stage and 500 psi in the second stage.

  • Pre-heating

    • Essential for destroying bacteria, inactivating enzymes, and producing antioxidant substances.
    • Skim milk is preheated at 85°C/185°F for 20 minutes, while whole milk is preheated at 93°C/200°F for 3 minutes.

Summary of Milk Powder Processing

• Lipid Content and Oxidation

  Whole milk powder, containing 26% fat, falls under the category of lipid-rich dairy products. Due to this high fat content, it is prone to developing an oxidized taste during storage.

• Preheating and Oxidation Control

  Preheating the milk to a specific temperature leads to a decrease in oxidation-reduction potential. This process liberates certain compounds that help prevent oxidation. It results in a palatable spray powder even after extended storage.

  Example: Efficient destruction of oxidizing enzymes during preheating helps maintain the powder's quality over time.

• Cooked Flavor and Stabilization

  Heating milk unavoidably introduces a cooked flavor. While this flavor is noticeable, it is not typically considered objectionable. Stabilizing milk without some level of heating would be challenging.

  Example: Liberation of sulfides of milk due to heat contributes to the cooked flavor.

• Condensing for Quality

  Dried milk made from precondensed fresh milk has superior keeping quality compared to milk that is not precondensed. Condensing under vacuum helps remove volatile substances, enhancing the powder's quality and stability.

  Example: Vacuum condensation aids in removing substances that may catalyze oxidation, thereby improving the keeping quality of the milk powder.

• Spray Drying Process

  Spray drying involves atomizing concentrated milk into fine droplets that mix with hot air in a drying chamber. The rapid evaporation of moisture results in the production of fine milk powder without the need for grinding.

  Example: The temperature of milk droplets during spray drying does not exceed a certain range, ensuring quality preservation.

• Cooling for Flavor Preservation

  After drying, it is crucial to promptly cool the milk powder to maintain its flavor, body characteristics, and overall quality. Delayed cooling can lead to the undesirable extraction of free fat, impacting the product's shelf life.

  Example: Rapid cooling below the fat's melting point is essential to preserve the milk powder's quality.

Packaging of Milk Powder

• Vacuum-operated fillers are used for packaging milk powder.
• The powder is packed in inert gas to prevent chemical reactions and extend storage life.
• Good quality milk powder can be stored for 6 months without gas packing if oxygen content is low.

Packaging Material

• Good packaging material should have low permeability to oxygen and moisture.
• Tin plate and sealed metal cans are ideal for packaging, while plastic and synthetic materials are also used.
• Laminates of materials like aluminum foils and polyethylene are developed for effective packaging.

Storage of Milk Powder

• Ideal storage temperatures for milk powder are lower than 24°C.
• Products should be stored in a vapor-proof, moisture-proof package in a cool, dark place.
• Refrigerated storage is recommended for long storage in warm climates.

Properties of Dried Milk Powder

• Roller-dried powder contains free fat and irregular particles, while spray-dried powder has spherical particles with enclosed air.
• Lactose is a major component of milk powder particles, forming an amorphous envelope.
• Bulk density of milk powder varies based on concentration, affecting solubility and wettability.

Milk Powder Quality Assessment

Judging and Grading of Milk Powder

• Good quality dried milk should flow readily, be free from lumps, and have a uniform white or light cream color.
• Proper packaging is crucial to maintain the quality of milk powder.
• The American Dairy Science Association provides a scorecard for both whole milk powder and skim milk powder.

Appearance Evaluation

• Inspect the can or bag for rust, both inside and out.
• Check for uniform color, absence of lumps, foreign particles, and signs of inadequate processing.
• Presence of foreign matter may indicate issues in the filtration and clarification processes.

Flavor Assessment

• Smell the milk powder immediately upon opening the container.
• Reconstitute the powder and taste to evaluate the flavor, which can vary based on the production process.
• Flavor defects like oxidized taint can develop during storage and can be prevented through various measures like inert gas packing and the addition of antioxidants.

Laboratory Testing

• Conduct laboratory tests following Indian Standard specifications to ensure the quality of milk powder.
• Tests should be performed as per the procedures outlined in IS:1165, 1967.

Summary: Uses of Milk Powder

Skim Milk Powder Uses:

• Skim Milk Powder is utilized in various applications:
• (i) It is employed in the creation of toned, double toned, and recombined milks.
• (ii) During milk scarcity, it is added to tea and coffee.
• (iii) It finds use in the production of ice cream.
• (iv) Skim Milk Powder is also integral to the making of candy and confectionery items.
• (v) It is a key ingredient in prepared foods.
• (vi) Used in the production of breads, rolls, biscuits, etc.
• (vii) Skim Milk Powder plays a role in the creation of cultured products.
• (viii) It is essential in making certain Indian sweets.

Preference for Spray Dried vs. Roller Dried Products:

• When complete reconstitution is necessary, a spray dried product is preferred.
• If complete reconstitution is not needed, a roller dried product, which is more economical, is used.

Whole Milk Powder Uses:

• Whole Milk Powder is employed in various ways:
• (i) It is used in preparing reconstituted milk.
• (ii) It is a common additive in tea and coffee.
• (iii) It is a key ingredient in the preparation of baby food.
• (iv) Whole Milk Powder is crucial in the production of candy, confectionery, bakery products, etc.

Comparison between Skim Milk Powder and Whole Milk Powder:

• The production and consumption of skim milk powder significantly surpasses that of whole milk powder.
• This difference is primarily due to the shorter shelf-life of whole milk powder compared to skim milk powder.