Chapter 19: Thermal Preservation: Hot and Cold Processing

Question 1

What is heat processing?

Answer 1

transfers heat energy into food and destroys

enzymes and bacteria (microorganisms) that cause spoilage and contamination

Question 2

What is cold processing?

Answer 2

pulls heat energy from food to slow molecular movement, thus slowing spoilage

Question 3

Cooking extends shelf life as long as what?

Answer 3

As the food is also packaged to prevent recontamination

Question 4

What is pasteurization?

Answer 4

low-heat treatment that destroys pathogenic microorganisms and stops enzyme activity

Question 5

What products are pasteurized?

Answer 5

Beer, wine, fruit juice, milk, oysters, and eggs

Question 6

The processing time and temperature depends on what?

Answer 6

depend on the microorganisms and enzymes in a food

Question 7

Batch pasteurization is best with what? What is batch pasteurization?

Answer 7

• Best with liquids

- Heated in a large vat with slow stirring, pumped over a cooling plate, then packaged and sealed

Question 8

What does high temperature-short time pasteurization (HTST) do?

Answer 8

• rapidly heats and cools liquids

- Liquids are pumped through heat exchangers, then cooling tubes, and immediately packaged and sealed

Question 9

HTST milk is heated to what temperature? For how long?

Answer 9

72oC for 15 seconds

Question 10

UHT milk is heated to what temperature? For how long?

Answer 10

140oC for 4 seconds

Question 11

Is UHT processing of milk pasteurizing? What does this process allow?

Answer 11

NO, it is sterilizing

- Lets consumers store milk or juice for several months without refrigeration

Question 12

What is commercial sterilization used for? What does it destroy?

Answer 12

– 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

Question 13

What do sealed cans prevent?

Answer 13

Recontamination and growth of any spores that may be present

Question 14

What does sterilization destroy? How is it accomplished? What is it limited to?

Answer 14

• Destroys microorganisms completely
• Accomplished by moist heat
• Limited to pureed or liquid foods

Question 15

What temperature are foods subjected to in sterilization?

Answer 15

121oC for 15 minutes

Question 16

What does aseptic mean?

Answer 16

Free of pathogens

Question 17

What does aseptic canning involve? How is it done?

Answer 17

involves sterilizing the food, placing it in sterilized containers, and sealing the containers
- heating food before packaging

Question 18

What are retorts?

Answer 18

Large commercial pressure canners with special locks and valves
- Temperature and pressure are monitored

Question 19

What is the difference between still and agitating retort?

Answer 19

• Still retort: cans don’t move, food is more likely to burn, temperature is limited
• Agitating: gently shake cans during processing

Question 20

What is the goal of thermal processing?

Answer 20

add enough heat energy to preserve a food product while maintaining as many original qualities as possible

Question 21

When is heat transfer by conduction used?

Answer 21

when food does not move in the container, such as corned beef hash, pumpkin pie filling, and tomato paste

Question 22

Is heat transfer by conduction or convection slower?

Answer 22

Conduction is slower because of less molecular motion in more-viscous food

Question 23

When is heat transfer by convection used? How does this process work?

Answer 23

• for liquids, purees, and chunks of food suspended in liquid
• sets up currents in liquids that speed the
  transfer of heat energy

Question 24

What is the cold point?

Answer 24

the last point in a can or mass of food to

reach the desired temperature

Question 25

Where is the cold point located when heating by conduction?

Answer 25

In the center of the can

Question 26

Where is the cold point located when heating by convection?

Answer 26

Just below the center of the can

Question 27

What is the thermal death curve?

Answer 27

the line plotted on a graph showing the time needed to destroy pathogens at a given temperature

Question 28

The lower the temperature, the longer the _____

Answer 28

cooking time

Question 29

How does sugar, starch, protein, fats and oils affect the heat-processing method?

Answer 29

interfere with wet heat penetrating the food

Question 30

How does fat affect the heat processing method?

Answer 30

Slow the conduction process

Question 31

Name 3 factors to consider when choosing a heat-processing method.

Answer 31

1) Safety (destroying microbes)
2) Food quality
3) Cost

Question 32

What are the 4 levels of heat preservation?

Answer 32

• Blanching
• Pasteurization
• Commercial sterilization
• Sterilization

Question 33

What is a method to heat food after packaging?

Answer 33

With a retort

Question 34

What is a method to heat food before pasteurization?

Answer 34

Pasteurization

aseptic canning