L9: Evaporation and Drying

Overview of Food Processing Regulations and Shelf Life

  • Insulation materials must not allow for leakage detection by inspectors.

  • Legal regulations dictate the visibility of potential leaks or shortcuts in processes.

Shelf Life of Low Acid Food Products

  • Low Acid Foods: Defined as foods with a pH level above 4.6.

    • Example of low acid food: Milk with a pH around 6.6.

    • High Acid Foods: Foods with a pH of 4.6 or lower, such as orange juice or apple juice.

  • Normal shelf life for milk post-pasteurization under proper refrigeration: 7 to 14 days, generally 11 to 14 days.

Concentration Processes in Dairy

Importance of Concentrating Milk

  1. Cost Reduction:

    • Concentration reduces costs associated with storage and transportation, as shipping concentrated milk (like powder) involves less water weight than fluid milk, which is 87% water.

  2. Induced Crystallization:

    • Example: Crystallizing lactose from liquid whey by removing water improves the crystallization process.

  3. Reduced Drying Costs:

    • Milk is first concentrated by evaporation before drying to powder, resulting in cost savings in the drying phase.

  4. Increased Microbial Stability:

    • Lower water content (water activity of 0.2 to 0.3) inhibits microbial growth.

  5. Recovery and Extraction of Byproducts:

    • Extraction of whey protein from liquid whey requires water removal for concentrate production.

Evaporation Processes

Overview of Evaporations

  • Evaporation typically involves indirect heating, often conducted under vacuum to lower the boiling point of water from 100 degrees Celsius to between 55 to 70 degrees Celsius, thus minimizing heat damage to milk components.

  • Heat transfer occurs from the heating medium (usually steam) to the milk; the steam condenses, releasing significant energy to evaporate water from the milk.

Equipment and Design of Evaporators

  1. Schematic of evaporation systems typically includes:

    • Vapor Separator: Main chamber where separation occurs.

    • Heating Source: Heat coil filled with steam to heat milk and evaporate water.

    • Condenser: Captures water vapor for reuse, showcasing water as a valuable resource.

    • For example, large plants might recycle up to 99% of the water from processing large quantities of milk.

  2. Steam Ejectors:

    • Remove non-condensable gases through a draft created by high-velocity steam, mixing these gases with steam and releasing them after treatment through foot print mechanisms like scrubbers.

Types of Evaporators

Circular Evaporators

  • Designed for lower evaporation degrees (10-20% removal of water).

  • Product enters at 90 degrees Celsius and is pumped tangentially into a vacuum chamber to flash off water vapor.

Falling Film and Rising Film Evaporators

  • Products flow through tubes where they are heated and evaporated, often observed in dairy processing.

  • Short contact time reduces nutrient degradation and flavor disruption.

Multi-Effect Evaporators

  • Features multiple evaporators connected in succession.

  • The vapor produced by the first evaporator is reused as steam for the next, enhancing efficiency by reducing energy consumption.

  • Known configurations include two, three, and up to seven effects, indicative of large-scale operations in the dairy industry.

Conclusion and Future Discussion

  • Plans to resume with discussions on midterms and further delve into additional processing details.