Chapter 20: Dehydration and Concentration: Controlling Water Activity

Question 1

What is Water Activity (Aw)?

Answer 1

Water activity is an indicator of perishability

Question 2

Reducing Water activity does what?

Answer 2

Reducing Water Activity can increase shelf life

Question 3

Categories of Processed foods preserved by reduced water activity are?

Answer 3

1. Dehydrated
2. Concentrated
3. Intermediate-moisture

Question 4

What is Dehydration?

Answer 4

The oldest method of food preservation

- caused by lowering water content

Question 5

In the Food Industry, What is Dehydration?

Answer 5

It is the artificial drying of food under controlled conditions
- functions to protect food spoilage

Question 6

What are the Benefits of Dehydration?

Answer 6

1. Lighter foods that take less space are less costly to package and ship
2. A more-convenient form of food

Question 7

Dehydrated foods are?

Answer 7

Left in a dehydrated state, like prunes and raisins

- Reconstituted by adding water, such as with instant mashed potatoes

Question 8

What does Dehydration do?

Answer 8

Dehydration preserves food by lowering the water activity level, thus preventing spoilage

Question 9

What is Surface Area and why is it important?

Answer 9

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

Question 10

If food is not dried enough what can happen?

Answer 10

If food is not dried enough, bacteria or mold can grow

Question 11

Dehydrators use what for drying?

Answer 11

Dehydrators use a heat source, a fan or a blower and a ventilated drying surface
- home food dehydrators operate on the same principle

Question 12

For every 15C (27F) rise in temperature what happens?

Answer 12

For every 15C (27F) rise in temperature, air holds twice as much moisture in vapour form

Question 13

What does faster drying mean?

Answer 13

Faster drying means less change in food quality

Question 14

What is a Case Hardening?

Answer 14

If drying is too rapid, a dry skin forms and traps moisture inside called case hardening

Question 15

Oxygen exposure causes what?

Answer 15

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

Question 16

Can Dehydration denature enzymes?

Answer 16

Dehydration temperature are not high enough to denature enzymes so many foods are pretreated to inactive enzymes

Question 17

What is Pasteurization?

Answer 17

Pasteurization is used with animal-based products like milk and eggs

Question 18

What is Blanching?

Answer 18

Blanching in boiling water is used with vegetables

Question 19

What is Sulfiting?

Answer 19

Sulfiting involves soaking food in a sodium bisulfite and water solution for 10 to 30 minutes

Question 20

What does Sulfiting do?

Answer 20

it extends drying time, may cause breathing difficulties for people allergic to sodium bisulfite

Question 21

What is Sulfuring?

Answer 21

it involves exposing fruits to fumes from burning sulfur for up to 4 hours

Question 22

What is a disadvantage to Sulfuring?

Answer 22

A disadvantage is that some people are allergic to sulfur dioxide

Question 23

What happens in Sulfuring?

Answer 23

Food is placed on stacked trays in a covered area where sulfur dioxide (SO2) can circulate
- may be dipped in sulfur dioxide

Question 24

What are some advantages of Sulfuring

Answer 24

Shortened drying time, inhibited mold growth due to sulfur dioxide fumes, and the ability of sulfur dioxide odours to repel insects

Question 25

What are the advantages of Sulfuring and Sulfiting?

Answer 25

Few or no effects on heat sensitive nutrients, food colour and texture - BOTH methods destroy thiamin

Question 26

What are the factors Food Processors consider when determining the best dehydration method?

Answer 26

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

Question 27

What is Tray Drying (Dehydration Method)?

Answer 27

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)

Question 28

What is Belt Drying (Dehydration Methods)?

Answer 28

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)

Question 29

What is Drum Drying (Dehydration Method)?

Answer 29

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

Question 30

What is Spray Drying (Dehydration Method)?

Answer 30

Very small drops of the food are sprayed into the top of a heated chamber or tower and dehydrate as they fall - The method is used with heat-sensitive product like milk, eggs, protein powders, flavourings and instant coffee - FASTEST drying method (can dehydrate food in seconds)

Question 31

What is Vacuum Drying (Dehydration Methods)?

Answer 31

Heated trays or shelves called "Platens" transfer heat in a vacuum chamber - Lowering the atmospheric pressure lowers the boiling point, minimizing heat damage - Produces HIGHEST quality (expensive) - Is used for fruit juices

Question 32

What is Freeze-drying (lypholization) or dehydrofreezing (Dehydration Method)?

Answer 32

Food is frozen, then placed in a vacuum chamber and heated - Food temperatures and atmospheric pressure are lowered until water sublimates - The process maintains better flavour and colour than other drying methods

Question 33

What is Oven Drying (Home-Dried Foods)?

Answer 33

Food is pretreated and arranged in single layers on each oven rack and then oven door is propped open slightly to create airflow - Oven temperature is maintained at 60C-66C (140F-150F) - Microwave ovens may be used to dry fresh herbs

Question 34

Foods that are about to undergo dehydration should be what?

Answer 34

Should be clean and free from blemishes - Drying should take place right after harvest - Trays need to be rotated every couple of hours

Question 35

Where should Home-dried foods be stored?

Answer 35

Home-dried foods should be stored in reclosable plastic bags - Food showing signs of mold growth should be discarded

Question 36

What is Rehydration?

Answer 36

some foods need to be rehydrated before eating them - Nonfat dry milk is dissolved in water before use - Instant potatoes or soup mixtures are added to boiling water and cooked until tender

Question 37

Why are some foods undergoing rehydration dusted with starch?

Answer 37

Foods such as raisins for breakfast cereal are dusted with starch to prevent moisture transfer

Question 38

What is Food Concentration?

Answer 38

Food concentration is removing a portion of the water from a food product - It may be the first step to dehydration

Question 39

What are Concentrates?

Answer 39

concentrates are foods that are reduced in volume by having part of their water removed, such as - fruit juice concentrate, maple syrup, condensed milk, and condensed soups

Question 40

What are the benefits of Concentrates?

Answer 40

Lowering shipped costs because of less volume and weight, extended shelf life and better handling ease prior to dehydration

Question 41

Some Problems with concentrates are?

Answer 41

Cooked flavours, colour changes, gritty textures, and denatured proteins

Question 42

Low-acid foods require what?

Answer 42

Low-acid foods require additional preservation methods to destroy pathogens

Question 43

What is the Open Kettle (Concentration Methods)?

Answer 43

Is the oldest way to remove water, requires frequent stirring, can result in flavour and colour changes with high heat and long cooking times - Is the method used to make some jams, jellies and condensed soups

Question 44

What is the Heat Evaporation Method (Concentration Method)?

Answer 44

food enters and leaves an evaporator in a continuous process - is exposed to high temperatures for short periods - has a fresher flavour than with the open kettle method because heat damage is limited

Question 45

What is Vacuum Evaporation (Concentration Method)?

Answer 45

A vacuum is added to the evaporator and food moves through a series of chambers, each with lower atmospheric pressure

Question 46

What is the Filtration Method?

Answer 46

Small particles pass through filters, isolating and concentrating the original food source

Question 47

What are Intermediate-Moisture foods?

Answer 47

have a moisture content of 20% to 50% with enough dissolved solutes to prevent the growth of microbes - Are nutrient and calorie dense because they are not concentrated - May or may not need refrigeration - May need preservatives or antioxidants added to prevent enzymatic activity