Freezing Flashcards
What is the most satisfactory method for long term food preservation?
Freezing
What is the temperature bracket that food being frozen at low-temperature levels uses?
18-30 degrees celsius
Why does freezing work so effectively at preserving food?
Because it removes free water that is required for microbial growth
How does freezing affect food quality?
Minimal nutritional impact, longterm freezing can impact the quality
If freezing is so expensive, why do companies use this process for foods?
To maintain shelf-life and decrease spoilage.
What must happen to uncooked produce to maximize food quality?
They must be blanched prior to freezing.
Describe the freezing curve.
The plot of temperature vs. time
What are the 3 distinct stages of freezing?
- Removal of sensible heat until freezing temperature
- Removal of latent heat leading to the formation of ice
- Further removal of sensible heat for storage
Why must produce cool pst 0 degrees?
For crystal formation
How come crystal formation causes an increase in temperature?
Because there is energy being released to form the crystals
How can one decrease the temperature for freezing?
By adding a solute such as salt.
How does salt decrease the freezing temperature?
Because as the ice is forming the rest of the concentration is being taken up by salt to the freezing point must go down.
Is there a clear freezing point for foods?
No, there is a range
What is the freezing point defined as?
The highest temperature at which ice crystals will form.
How does the rate of freezing impact crystal growth?
Slower freezing leads to a limited amount of ice crystals which grow to be quite large.
How does rapid freezing effect foods?
There is a higher number of smaller ice crystals. This maintains cell rigidity and minimizes loss of water.
Why might the quality of frozen foods go down slowly?
Because of the denaturation of muscle proteins as the unforzen region becomes concentrated with enzymes, proteins denature and affect the function.
How can protein denaturation be prevented?
Rapid freezing so the ice crystal formation zone passes quickly
What is the ice crystal formation zone?
0-5 degrees
What factors effect rate of freezing? (5)
- temperature difference between food and cooling medium
- Heat transfer rate of cooling medium
- Surface area of food
- Product thickness
- Agitation of product (mixing)
What is the concern with a freezer which fluctuates in temperature?
Upon refreezing the ice crystal size increases and disrupts cell walls losing texture.
What may cause freezer burn?
A decrease in humidity may lead to sublimation (solid to gas) of ice. this discolours food and denature protein. Texture is lost and rancidity develops.
What should relative temperature humidity be kept at and why?
90% to reduce air movement across food products.
What is glazing and how does it protect food?
The formation of a layer of water prior to freezing protects food from moisture loss.
