Flashcards in Chapter 20: Dehydration and Concentration: Controlling Water Activity Deck (47)
What is Water Activity (Aw)?
Water activity is an indicator of perishability
Reducing Water activity does what?
Reducing Water Activity can increase shelf life
Categories of Processed foods preserved by reduced water activity are?
What is Dehydration?
The oldest method of food preservation
- caused by lowering water content
In the Food Industry, What is Dehydration?
It is the artificial drying of food under controlled conditions
- functions to protect food spoilage
What are the Benefits of Dehydration?
1. Lighter foods that take less space are less costly to package and ship
2. A more-convenient form of food
Dehydrated foods are?
Left in a dehydrated state, like prunes and raisins
- Reconstituted by adding water, such as with instant mashed potatoes
What does Dehydration do?
Dehydration preserves food by lowering the water activity level, thus preventing spoilage
What is Surface Area and why is it important?
Surface area is an important factor; because the greater the exposed surface area is, the faster the food dries
ie) Thin uniform pieces speed the process
If food is not dried enough what can happen?
If food is not dried enough, bacteria or mold can grow
Dehydrators use what for drying?
Dehydrators use a heat source, a fan or a blower and a ventilated drying surface
- home food dehydrators operate on the same principle
For every 15C (27F) rise in temperature what happens?
For every 15C (27F) rise in temperature, air holds twice as much moisture in vapour form
What does faster drying mean?
Faster drying means less change in food quality
What is a Case Hardening?
If drying is too rapid, a dry skin forms and traps moisture inside called case hardening
Oxygen exposure causes what?
Oxygen exposure causes formation of tannic acid (browning) in foods high in polyphenols such as apples, grapes and tea
- increasing surface area increases exposure to oxygen
Can Dehydration denature enzymes?
Dehydration temperature are not high enough to denature enzymes so many foods are pretreated to inactive enzymes
What is Pasteurization?
Pasteurization is used with animal-based products like milk and eggs
What is Blanching?
Blanching in boiling water is used with vegetables
What is Sulfiting?
Sulfiting involves soaking food in a sodium bisulfite and water solution for 10 to 30 minutes
What does Sulfiting do?
it extends drying time, may cause breathing difficulties for people allergic to sodium bisulfite
What is Sulfuring?
it involves exposing fruits to fumes from burning sulfur for up to 4 hours
What is a disadvantage to Sulfuring?
A disadvantage is that some people are allergic to sulfur dioxide
What happens in Sulfuring?
Food is placed on stacked trays in a covered area where sulfur dioxide (SO2) can circulate
- may be dipped in sulfur dioxide
What are some advantages of Sulfuring
Shortened drying time, inhibited mold growth due to sulfur dioxide fumes, and the ability of sulfur dioxide odours to repel insects
What are the advantages of Sulfuring and Sulfiting?
Few or no effects on heat sensitive nutrients, food colour and texture
- BOTH methods destroy thiamin
What are the factors Food Processors consider when determining the best dehydration method?
1. The type of food
2. What quality is desired
3. How much consumer are willing to pay
4. Whether food is whole, divide, pureed or liquid
What is Tray Drying (Dehydration Method)?
Food is held on trays with holes in an enclosed cabinet for up to 20hours
- Air is blown over the food or rises up through the trays
- Moisture-filled air is vented out of the system
(This method is small-scale operations for fruits and vegetables)
What is Belt Drying (Dehydration Methods)?
This methods continuously feeds food into a tunnel dehydrator on moving belts
- Food can reach moisture levels of 5% to 7% in as little as 1 hour
- Using a belt Trough dryer causes food to tumble for even drying
(grains, peas, and beans work best in this dryer)
What is Drum Drying (Dehydration Method)?
Rotating heated drums pick up food and dry it as the drums rotate
- The drying time needed determines the size of the drum and the speed of rotation
- The method is best with heat-resistant foods that are brittle when dry like...
mashed potatoes, mashed sweet potatoes and tomato pastes