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UPSC MainsANI-HUSB-VETER-SCIENCE-PAPER-II202515 Marks
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Q25.

List out different defects encountered in condensed and evaporated milk, their causes and preventive measures.

How to Approach

To answer this question effectively, candidates should first define condensed and evaporated milk to set the context. The main body should systematically categorize defects as microbial and non-microbial (physical/chemical) for both types of milk. For each defect, a clear cause and corresponding preventive measure must be provided. Using a table format can enhance readability and comparison. The conclusion should summarize the importance of quality control in dairy processing.

Model Answer

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Introduction

Condensed and evaporated milk are concentrated dairy products, differentiated primarily by the addition of sugar in condensed milk and the sterilization process in evaporated milk, both designed for extended shelf life. Despite their processing for preservation, these products are susceptible to various quality defects that can compromise their sensory attributes, shelf stability, and consumer appeal. Understanding these defects, their underlying causes, and implementing effective preventive measures are crucial for dairy manufacturers to ensure product quality and safety, thereby maintaining consumer trust and adhering to food standards. These defects can broadly be categorized into microbial and non-microbial (physical and chemical) issues.

Maintaining the quality of condensed and evaporated milk throughout their shelf life is paramount for consumer satisfaction and economic viability. Defects can arise from raw milk quality, processing parameters, packaging, or storage conditions.

Defects in Sweetened Condensed Milk

Sweetened condensed milk is preserved primarily by its high sugar concentration, which reduces water activity and inhibits microbial growth. However, several defects can still occur:

Defect Cause Preventive Measures
1. Sandiness (Lactose Crystallization)
  • Formation of large lactose crystals due to inadequate cooling, insufficient seeding with fine lactose crystals, or fluctuating storage temperatures.
  • Supersaturation of sucrose when the ratio in the finished product exceeds 64.5%.
  • Rapid and uniform cooling of the condensed milk.
  • Seeding with fine lactose crystals during cooling to promote small, uniform crystal formation.
  • Maintaining optimum storage temperature (e.g., 10-15°C) and avoiding very low temperatures.
  • Ensuring complete solution during the evaporation process.
2. Age Thickening (Gelling)
  • Progressive increase in viscosity during storage, leading to a semi-solid or jelly-like consistency.
  • Can be caused by bacterial activity (microorganisms producing rennin-like enzymes) or physico-chemical reactions (e.g., protein aggregation).
  • Improper preheating of milk, high total solids concentration, inadequate homogenization, and storage at high temperatures.
  • Efficient sanitary practices and controlled forewarming temperatures to destroy causative microorganisms.
  • Maintaining an optimum sucrose-to-water ratio (around 64.5%) to inhibit bacterial growth.
  • Optimizing preheating temperature and concentration levels.
  • Storing the product at low temperatures (below 15°C).
  • Use of stabilizers to a certain extent.
3. Gassy Fermentation (Bloats)
  • Contamination by gas-producing yeasts (e.g., Torulopsis spp.) or bacteria (e.g., Clostridium species) during processing or packaging.
  • Sources of contamination: raw milk, inferior quality sugar, unhygienic equipment, or improper sealing of containers.
  • Strict adherence to hygiene and sanitation standards throughout the manufacturing process.
  • Using high-quality raw milk and sugar.
  • Proper sterilization of equipment and containers.
  • Ensuring proper sealing of cans.
4. Mould Buttons
  • Growth of osmophilic molds (e.g., Aspergillus repens, Penicillium spp.) on the surface or subsurface, forming reddish-brown lumps.
  • Occurs due to contamination and sufficient air in the headspace of the container.
  • Scrupulous cleaning and sanitization of dairy equipment.
  • Filling containers fully to minimize headspace air.
  • Proper sealing.
  • Maintaining low storage temperatures.
5. Rancid Flavour
  • Hydrolysis of fat by lipase enzyme, leading to the production of free fatty acids (e.g., butyric acid).
  • Forewarming fresh milk at temperatures above 76°C to inactivate lipase.
  • Using good quality raw milk.
6. Brown Colour (Browning/Darkening)
  • Maillard reaction between milk sugars and amino acids, accelerated by intense heat treatment during forewarming and high storage temperatures.
  • Storing condensed milk cans at reasonably low temperatures (e.g., 10-15°C).
  • Optimizing preheating temperatures to avoid excessive heat load.

Defects in Evaporated Milk

Evaporated milk undergoes sterilization, making it commercially sterile. However, it is still prone to specific physical and chemical defects:

Defect Cause Preventive Measures
1. Age Thickening/Gelling
  • Protein destabilization and aggregation during prolonged storage, intensified by high storage temperatures and excessive heat treatment during sterilization.
  • High protein stability or protease activity from psychrotrophic bacteria in raw milk.
  • Applying only the necessary and effective heat treatment for sterilization.
  • Ensuring raw milk has a low bacterial count.
  • Adequate preheating.
  • Storing products at cool temperatures (e.g., 5°C or below).
  • Use of appropriate stabilizers (e.g., disodium phosphate).
2. Age Thinning/Low Viscosity
  • Milk-like consistency due to insufficient concentration of milk solids, inadequate or no homogenization, or improper sterilization.
  • Following correct and adequate processing conditions, including proper concentration.
  • Ensuring proper homogenization of the milk.
  • Storing the product at low temperatures.
3. Fat Separation (Cream Plug)
  • Inadequate homogenization, poor fat globule stabilization, or prolonged agitation during handling and storage.
  • Abnormally low viscosity.
  • Efficient high-pressure homogenization to create small, stable fat globules.
  • Use of stabilizers (e.g., disodium phosphate) to prevent fat aggregation.
  • Careful handling to avoid excessive vibration during transport and storage.
  • Proper concentration of total solids.
4. Browning (Maillard Reaction)
  • Heat-induced reaction between lactose and proteins/amino acids during sterilization and subsequent storage.
  • High sterilization temperature, high storage temperature, and longer storage period.
  • Minimizing heat load during processing.
  • Adopting the lowest effective sterilization temperature.
  • Storing the product at cool conditions (e.g., 5°C or below).
  • Using fresh milk with less protein degradation.
5. Sedimentation (Mineral Deposit)
  • Formation of a whitish, gritty deposit, mainly tri-calcium citrate, near the bottom of the container.
  • Occurs during prolonged storage, influenced by milk quality, manufacturing conditions, and storage temperature.
  • Selection of good quality raw milk.
  • Correct processing conditions.
  • Low-temperature storage.
  • A higher viscosity product is less prone to this defect.
6. Gassy Fermentation/Bloats
  • Survival of heat-resistant microorganisms and spores (e.g., Bacillus spp.) due to inadequate sterilization, leading to gas production.
  • Post-processing contamination.
  • Strict adherence to proper and adequate sterilization processes.
  • Maintaining scrupulous cleanliness in the factory to prevent post-processing contamination.
7. Metallic/Stale Flavour
  • Contact with certain metals during processing or fat oxidation during storage.
  • Use of properly lined cans and inert equipment.
  • Oxygen-limiting packaging.

Conclusion

The quality and marketability of condensed and evaporated milk are significantly influenced by the absence of various defects, ranging from textural inconsistencies like sandiness and gelling to flavor alterations and microbial spoilage. These defects are often rooted in a combination of raw material quality, sub-optimal processing parameters (heat treatment, homogenization, concentration), and inappropriate storage conditions. Implementing stringent quality control measures, adhering to Good Manufacturing Practices (GMP), regular equipment sanitation, and precise temperature management at all stages of production and storage are critical. Continuous monitoring and technological advancements in dairy processing are essential to consistently deliver high-quality, safe, and appealing concentrated milk products to consumers.

Answer Length

This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.

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Additional Resources

Key Definitions

Condensed Milk
Milk from which a substantial portion of water has been removed by evaporation, typically containing added sugar (sweetened condensed milk) to act as a preservative, extending its shelf life without requiring sterilization.
Evaporated Milk
Milk from which about 60% of the water has been removed by evaporation, and which is then homogenized, sealed in cans, and heat-sterilized, making it commercially sterile and shelf-stable without added sugar.

Key Statistics

The global market for condensed milk was valued at approximately USD 12.8 billion in 2022 and is projected to grow, highlighting the continuous demand and the need for stringent quality control to prevent defects. (Source: Various market research reports, e.g., Grand View Research)

Source: Grand View Research (example)

Studies indicate that improper storage temperatures (above 25°C) can accelerate age thickening and browning reactions in evaporated milk by 2-3 times compared to ideal cold storage conditions (below 5°C), significantly reducing shelf life. (Source: Dairy Science and Technology Journals)

Source: Dairy Science and Technology Journals (example)

Examples

Impact of Inadequate Homogenization

A common issue in evaporated milk without proper homogenization is the "cream plug" defect. This occurs when larger fat globules, not adequately reduced in size during homogenization, coalesce and rise to the top of the can, forming a thick, undesirable layer of fat upon opening. This impacts both appearance and texture.

Sugar Quality and Sandiness

If the sugar used in sweetened condensed milk is of poor quality or not completely dissolved, it can contribute to the "sandiness" defect by providing larger sugar crystals that act as nuclei for further crystallization, resulting in a gritty texture.

Frequently Asked Questions

▶Can consuming milk with these defects be harmful?

While some defects like sandiness or age thickening are primarily aesthetic and textural, making the product unpalatable but not necessarily harmful, microbial defects like gassy fermentation can indicate the presence of spoilage microorganisms. In such cases, consuming the product could lead to digestive upset or foodborne illness, making it unsafe.

▶What role does packaging play in preventing defects?

Packaging is crucial. For evaporated milk, hermetically sealed cans are vital for maintaining sterility. For both, proper sealing prevents re-contamination and limits oxygen exposure, which can cause oxidation-related off-flavors. Appropriate packaging also protects against physical damage and maintains an optimal internal environment.

Topics Covered

Food TechnologyDairy ScienceDairy ProductsMilk ProcessingQuality Control
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