Purposes of Cooling

• To Prolong Product Quality
• To Increase Shelf-Life
• To Slow post-harvest or post-slaughter physiological changes
• To slow microbial growth
• To slow enzyme activity
• To make some foods possible

• Chilling in Air
• Indirect Contact Chilling
• Direct Contact/Immersion Chilling

Chilling in Air

• Still Air
• High-velocity Air
• Fluidized Bed

The food or package is in contact with a surface that is cooled by a refrigerant, but the food or package does not contact he refrigerant directly

• plate heat exchanger
• tubular heat exchanger

• Direct contact of the food and refrigerant
  • Cold water spray
• Submerging a food or spraying cold liquid onto the food or package
  • Submerging food in ice water or cryogenic fluids
• Allows for intimate contact with the refrigerants
  • Storing on Ice

• Chill Injury of Fresh Produce
• Flavor Migration between foods
• nutrient loss
• retrogradation of starch
• Oxidative rancidity of lipids
• Enzymatic Reactions
• Water Migration
• Growth of Spoilage Organisms

• Most microorganisms and pathogens don't grow at refrigeration temperatures
• Pseudomonas does
  • counts can increase by a factor of 10 in 24 hrs at 7⁰C 
  • produces heat stable proteases and lipases that are a concern in food

• proteins can denature
• carbohydrates can come out of solution
• acid concentration increases
• gas pressure increase

Intermittent thawing and freezing of a product, as often occurs during temperature cycling

• does not require total change of ice to liquid

Rate of Freezing

(results in, and is essential for)

• Results in more, homogeneously dispersed ice nuclei
• essential to preserving food quality

• Bursts their cells and dries them out
• Can kill higher level pathogens

• Wind Speeds up to 30-40 mph
• Disadvantages: larger temperature gradient, expensive, dries out product

• Use of high velocity air to separate particles
• Often done with "Individually Quick Frozen" foods 
• Freezes so quickly that no case hardening occurs

1. Cooling to "freezing point"
2. supercooling until...
3. NUCLEATION
4. Heat is released and local temperature increases
5. further cooling will cause more ice to grow on existing crystals