1. Processing Food by Heat
Can destroy microorganisms
Can denature enzymes
Can increase shelf life of food with appropriate packaging
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2. Four Levels of Heat Preservation
Blanching
Submerging food for short time in boiling water or steam
Stops enzyme activity
Helps to prevent undesirable flavor, texture, and color changes of the food
Used for pretreating fruits (sometimes with a syrup blanch) and vegetables
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3. Four Levels of Heat Preservation
Commercial Sterilization
Destroys microorganisms that cause illness, bring about food spoilage, or create toxins
Processed in sealed containers
Prevents resistant bacterial spores from reproducing and making them inert
May produce flavor and texture changes in the food
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4. Four Levels of Heat Preservation
Pasteurization
Heating foods just below the boiling point
Stops enzyme activity and destroys pathogens
Used for foods, such as eggs, fruit juices, milk, and oysters
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5. Four Levels of Heat Preservation
Sterilization
Completely destroys all microorganisms
Different microbes require varying temperatures and sustained times
Wet heat (food is in the presence of water or moisture from steam) must be sustained at a temperature of 250°F for 15 minutes to kill all microbes
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6. Factors Affecting Processing Method
Heat Transfer - extremely important factor in order to maintain the integrity of food product
Conduction
Foods do not move in the can
Food processed as energy from molecular collisions is passed from the outside food layer in the can to the cold point in the center of the can
Convection
Liquid in the can is heated resulting in currents, which cause the liquid to become less dense, rise to the top, and thus, speeding the transfer of heat energy throughout the can of food
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7. Factors Affecting Processing Method
Food Components
Type of microbe in food determines processing method
Food size and density can affect the choice of processing method
Some ingredients, such as fats, oils, protein, starch, and sugar, protect the microbe from heat, making it important to raise the temperature and increase the processing time
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8. Factors Affecting Processing Method
pH of the Food
Low-acid foods have a pH of 4.6 and higher
C. botulinum can survive and multiply
Can be deadly
Must process these foods at higher temperature
High-acid foods have a pH between 2.0 and 4.6
Can be processed at lower temperatures than low- acid foods
Boiling temperature (212°F) will destroy
most microbes
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9. Factors Affecting Processing Method
Time and Temperature
Must balance the ability to kill pathogens with the effect of high heat on food quality
Thermal death curve – line graph that illustrates how long it will take to kill a microorganism at a certain temperature
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11. Commercial canning Processes vs. Home canning Processes
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12. Commercial canning Processes
Points to consider
Method must kill harmful microorganisms
Method must maintain the quality of the food while destroying microorganisms
Method must be a reasonable cost including equipment, energy use, packaging, and shipping costs
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13. Commercial canning Processes
Heating food after packaging
Retort – huge pressure canners with a large, sealed chamber
Agitation retorts – adds movement which stimulates liquids which are heated quicker than food
Pouch retorts – pouches replace other containers – processing time is shortened because heat penetrates the pouch quicker
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14. Commercial canning Processes
Heating food after packaging
Hydrostatic Cooker and Cooler
Filled bottles, cans, and jars more continuously through a U-shaped tube filled with water and steam
Temperature and pressure inside the tube change during the processing period
Home canning methods
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15. Commercial canning Processes
Heating food before packaging
Requires sterile conditions only found in commercial processing
Batch Pasteurization
Mostly used with liquids, such as milk
Heat liquid, fill container, seal, process
Aseptic canning
Sterilized food is placed in sterilized container
Requires careful monitoring
Temperatures can go as high as 302°F
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16. Home canning Processes
Packing Methods
Cold pack
Raw food is packed in jars, filled with a boiling liquid, closed with a lid, and then processed
Used for foods that are easily damaged
Hot pack
Food is heated in a liquid or syrup to 171°F and packed in jars while still hot; then jars are sealed and processed
Foods, such as corn, can be packed more tightly if heated prior to packing
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18. Cold Processing Food Preservation
Cold processing methods will not destroy microorganisms in the food.
Cold process methods will not denature enzymes.
Cold processing slows down the growth of (chemical reaction rate) microorganisms if they are already present in the food, but may grow and multiply when the food is thawed unless the food is carefully handled.
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19. Cold Processing Food Preservation Terminology
Blast freezer
Cryogenic liquids
Freeze drying
Freezer burn
Humidity
Immersion freezing
Indirect contact freezing
Lyophilization
Refrigerant
Respiration
Sharp freezing
Sublimation
Syneresis
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