Low Temp Preservation Flashcards
T or F
Poor maintenance and equipment care of freezers lead to formation of small ice crystals
F.
Small -> large ice crystals
How do people used to store food?
- In cold cellars
- holes in the ground
- Natural Caves
Post____ metabolic activities of intact plant tissues and post____ metabolic activities of animal tissues
plant: postharvest
animal: post slaughter
What happens in Freeze concentration effect?
-Loss of consistency
-syneresis
-chemical reaction
T or F: fungicide is used in hydro coolers
True but sometimes only
When was mechanical refrigeration introduced
Later 1800s
Major disadvantage of chest freezer
Slow freezing
Cook-chill process
- Cook
- Chill
- Store
- Regeneration & service
Produces small crystals, necessary for high quality products such as ice cream
Fast freezing
Applied mainly for prepacked vegetables with large surface area
Vacuum coolers
Chest freezers are relatively ____, ____, and _____.
Simple, versatile, cheap
Why is chilling vital in sous vide
Induce thermal shock to microorganism
T or F
Refreezing is microbiologically okay if temperature is high.
F. High -> Low
Requirements for growth of microorganism
- prefer water
- cannot tolerate high sugar/salt
- cannot tolerate alcohol
- optimum temperature
Use of chill water, either by spraying or immersion
Hydro coolers
On what food is hydro cooler used
Produce with thick skin so water cannot penetrate
Types of Chest freezers and difference between the two
Chest Freezer retain cold air
Cabinet System lose cold air when door is opened
T or F
Blast Freezing facility can freeze food items within 30 minutes.
F. Blast Freezing -> Individually Quick Freezing (IQF)
Freezing is the unit operation in which the temperature of a food is reduced below the __________ and a proportion of the water undergoes a _________ to form ______.
-freezing point
-phase change
-ice
T or F
Thawing is usually less controlled than freezing (or accidental).
True
Chilling temperature
Above freezing and below 15 C
Steps in Refreezing
-remanufacture
-cook and refreeze
-test for microorganisms if not sure
Application of heat until the ice present has reverted to water
Thawing
True or False
Thawing could be more damaging than freezing
True
Pressure when using vacuum cooler
0.5 kPa
Two ways of freezing fruits
- Sugar pack
- Syrup pack
Raw materials are cooked under controlled conditions of temp and time inside heat-stable vacuumized pouches
Sous vide
How are vegetables hydro cooled in wet markets in the philippines
Spraying with cold water (household method)
Deteriorative chemical reactions
- chemical changes associated with color degradation
- autolysis of fish
- loss of nutritive value of foods in general
4 types of cooled air freezers
Chest freezers
Blast freezers
Belt freezers
Fluidized bed freezers
Main Goal of Preservation
prevent microoranism from growing
T or F: Microorganisms still grow at 15 C
True but activity is only slowed down
Why are tomatoes injured when refrigerated
Carotenoids are not fully developed
How do hydro coolers work
Produce on conveyor belt and showered with cold water
Blast freezers utilizes _____ which are slower than ______.
-fast freezing
-plate freezer
T or F: Potharvest metabolic activities are still present during refrigeration
True but activities are only slowed down
Problems in Blast freezers
-Moisture loss
-High capital cost
What do wrinkles in food indicate
Moisture loss
Causes shrunk cells and destructed tissue, not good for industry use.
Slow Freezing
What happens in large ice crystal damage and recrystallization?
-Physical rupture of cell walls and membranes & separation of plant & animal cells
-Disruption of emulsion, foams, and gels
Means under vacuum
Sous vide
Chest freezers is used as
storage after freezing
Maximum chilling storage time and temp in sous vide
Up to 21 days, 0-3 C
The ______ component of a food freezes first and leaves the _____ in a more concentrated solution, which requires a ________to freeze.
-water
-dissolved solids
-lower temperature
Optimum temperature of eggplant
10 C
Air conditions in blast freezers
-400m/min→ rapid heat transfer
-Temperature: -25 to -36°C
What are the 2 principles of freezing food?
-Lowering of temperature by removal of heat in food
-change of phase from liquid to solid (water to ice)
__________ pattern of thawing potentially more detrimental than freezing.
Time-temperature
Keri pa ba mag review sis? :((
Wala kang choice :)
_______ during thawing is less than in freezing.
Temperature differential
T or F
In order for a product to freeze, the product must be cooled above its freezing point.
F. Above -> Below
What is an ice box
Closed, wooden box that contained a block of ice in a chamber above the food to keep it cold
Cold storage facility provides __- __ yrs shelf life
2-3 yrs
T or F: fruits and vegetables have optimum storage temperature like microbes
True
Cold loving microorganisms that will eventually spoil food
Psychrophile
added in storing food items to occupy headspace and prevent freezer burn
Parchment paper or plastic (cling wrap) or Freezer wrap
Optimum temperature of eggplant
10 C
2 Quality changes in Fast Freezing
-Freeze concentration effect
-Large ice crystal damage and recrystallization
Difference between Chest Freezer and Blast Freezers
Chest freezer uses still air, Blast freezer has super cooled air
T or F: Foods will never spoil under refrigeration
False, just a slower process
Do you think refreezing is encouraged? Yes or No? ^____^
NOOOOOOO!!!! >:((
As much as possible, do not refreeze
Tips in preventing freezer burn
-Remove headspace in food packages through vacuum pack
-Repackage food items in plastic bas and remove air before storing
-Put plastic wrap/freezer wrap/parchment paper with food items inside the container to prevent moisture vapor
What results after production of gases, slime, pigments and enzymes
- Softening
- rotting
- off-flavors and odors
- breakdown of food components
Cold Storage System includes (VIDEO)
Cold storage facility
Blast freezer facility
Individually Quick Freezing (IQF) facility
Results to less damaged tissue with maintained integrity, good for industry use.
Fast freezing
Dangers of sous vide
- Pasteurizing does not reduce pathogenic spores to a safe level
- foods which are safe for sous vide are limited
- if not chilled rapidly enough or refrigerated too long, pathogenic spores can outgrow and multiply to dangerous levels
Difference of traditional cooking and sous vide
Traditional: cooked directly in a pot
Sous vide: packed and cooked using precisely controlled heating
Main considerations in thawing
-avoid overheating
-minimize thawing times
-avoid excessive dehydration of the food
Purpose of rapid chilling in sous vide
To stop the cooking process
What was the means of cold preservation in the middle 1800s
Ice
T or F
Change of water into ice will result in the increase of concentration of unfrozen matrix, leading to dehydration and lowering of water activity.
T
______ must not suffer in refreezing because it is ______.
-Quality
-product dependent
What type of container used in sous vide
Laminated plastic pouch or container
T or F
Foods have different freezing point.
T
In what type of food service is cook-chill process is applied
Quick-service restaurants and Commissary food service
Air speed and temperature of blast chiller
4 m/s and 4 C
Why is refrigeration good for preventing microorganism growth but unacceptable for food quality?
Microorganism growth: moisture loss
Food Quality: dries out produce
Injury in frozen food which occurs when there is a headspace in the packaged food and the food is subjected to fluctuating storage temperatures
Freezer Burn
T or F
Thawing is generally faster than freezing.
F. Faster -> slower
Operate by passing cold air over foodstuffs at high speed
Blast chiller
What type of environment is naturally cold
Environment with rocks
Minimum recommended thermal process for sous vide
90 C for 10 min or it’s t-T equivalent (combination of time and temperature)
Types of Blast Freezer
-Spiral
-Cabinet
-Belt
How to prevent moisture loss
Wrap the food
Process of sous vide
- Raw or parcooked food
- Vacuum sealing
- Heat treatment
- Rapid chilling
- Reheated for service
Benefits of vacuum sealing
- Inhibits off flavors from oxidation
- prevents evaporative losses of flavor volatiles and moisture
- reduce aerobic bacterial growth (results in especially flavorful and nutritious food)
What happens to mangoes under refrigeration
Skin defects due to abnormal continuation of physiological growth
what causes moisture loss in the refrigerator
relative humidity
T or F: Using hydro coolers has the risk of freezing
False
