Chapter 19: Thermal Preservation: Hot and Cold Processing Flashcards
What is heat processing?
transfers heat energy into food and destroys
enzymes and bacteria (microorganisms) that cause spoilage and contamination
What is cold processing?
pulls heat energy from food to slow molecular movement, thus slowing spoilage
Cooking extends shelf life as long as what?
As the food is also packaged to prevent recontamination
What is pasteurization?
low-heat treatment that destroys pathogenic microorganisms and stops enzyme activity
What products are pasteurized?
Beer, wine, fruit juice, milk, oysters, and eggs
The processing time and temperature depends on what?
depend on the microorganisms and enzymes in a food
Batch pasteurization is best with what? What is batch pasteurization?
- Best with liquids
- Heated in a large vat with slow stirring, pumped over a cooling plate, then packaged and sealed
What does high temperature-short time pasteurization (HTST) do?
- rapidly heats and cools liquids
- Liquids are pumped through heat exchangers, then cooling tubes, and immediately packaged and sealed
HTST milk is heated to what temperature? For how long?
72oC for 15 seconds
UHT milk is heated to what temperature? For how long?
140oC for 4 seconds
Is UHT processing of milk pasteurizing? What does this process allow?
NO, it is sterilizing
- Lets consumers store milk or juice for several months without refrigeration
What is commercial sterilization used for? What does it destroy?
– is used for canned foods in sealed containers
– is a method used commercially as well as for foods canned at home
– destroys all microorganisms that cause illness, produce toxins, or result in spoilage
What do sealed cans prevent?
Recontamination and growth of any spores that may be present
What does sterilization destroy? How is it accomplished? What is it limited to?
- Destroys microorganisms completely
- Accomplished by moist heat
- Limited to pureed or liquid foods
What temperature are foods subjected to in sterilization?
121oC for 15 minutes
What does aseptic mean?
Free of pathogens
What does aseptic canning involve? How is it done?
involves sterilizing the food, placing it in sterilized containers, and sealing the containers
- heating food before packaging
What are retorts?
Large commercial pressure canners with special locks and valves
- Temperature and pressure are monitored
What is the difference between still and agitating retort?
- Still retort: cans don’t move, food is more likely to burn, temperature is limited
- Agitating: gently shake cans during processing
What is the goal of thermal processing?
add enough heat energy to preserve a food product while maintaining as many original qualities as possible
When is heat transfer by conduction used?
when food does not move in the container, such as corned beef hash, pumpkin pie filling, and tomato paste
Is heat transfer by conduction or convection slower?
Conduction is slower because of less molecular motion in more-viscous food
When is heat transfer by convection used? How does this process work?
- for liquids, purees, and chunks of food suspended in liquid
- sets up currents in liquids that speed the
transfer of heat energy
What is the cold point?
the last point in a can or mass of food to
reach the desired temperature
Where is the cold point located when heating by conduction?
In the center of the can
Where is the cold point located when heating by convection?
Just below the center of the can
What is the thermal death curve?
the line plotted on a graph showing the time needed to destroy pathogens at a given temperature
The lower the temperature, the longer the _____
cooking time
How does sugar, starch, protein, fats and oils affect the heat-processing method?
interfere with wet heat penetrating the food
How does fat affect the heat processing method?
Slow the conduction process
Name 3 factors to consider when choosing a heat-processing method.
1) Safety (destroying microbes)
2) Food quality
3) Cost
What are the 4 levels of heat preservation?
- Blanching
- Pasteurization
- Commercial sterilization
- Sterilization
What is a method to heat food after packaging?
With a retort
What is a method to heat food before pasteurization?
Pasteurization
aseptic canning
