Course:FNH200/Lessons/Lesson 07/Page 07.1

7.1 Use of Low Temperatures in Food Preservation

Terms to remember

Psychrotrophic Modified atmosphere packaging (MAP) Freezing point Latent heat Concentration effects Freezer burn Freezing rate IQF(individually quick frozen) Indirect contact freezers Cryogenic water vapour

Refrigeration or cool storage generally refers to storage at temperatures above freezing, while freezing and frozen storage occur at temperatures below freezing. However, whereas pure water freezes at 0°C, most foods do not begin to freeze until a temperature of -2°C or lower is reached.

Refrigerated or cool storage generally will preserve most perishable foods for days or weeks, while good frozen storage conditions with proper packaging can preserve foods for months or even years.

It should be noted that some psychrotrophic pathogens (review terminology in Lesson 5) can grow, although slowly, at refrigerator temperatures, and some spoilage organisms can even grow at temperatures below 0°C providing that there is unfrozen water available.

Below -9.5°C, there is no significant growth of spoilage or pathogenic organisms, and there is a gradual decrease in numbers of living organisms. However, freezing and frozen storage do not lead to complete destruction, and rapid growth and multiplication can occur during thawing.