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FDSC 200 > Chapter 20: Dehydration and Concentration: Controlling Water Activity > Flashcards

Chapter 20: Dehydration and Concentration: Controlling Water Activity Flashcards

1
Q

What is Water Activity (Aw)?

A

Water activity is an indicator of perishability

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2
Q

Reducing Water activity does what?

A

Reducing Water Activity can increase shelf life

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3
Q

Categories of Processed foods preserved by reduced water activity are?

A
  1. Dehydrated
  2. Concentrated
  3. Intermediate-moisture
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4
Q

What is Dehydration?

A

The oldest method of food preservation

- caused by lowering water content

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5
Q

In the Food Industry, What is Dehydration?

A

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

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6
Q

What are the Benefits of Dehydration?

A
  1. Lighter foods that take less space are less costly to package and ship
  2. A more-convenient form of food
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7
Q

Dehydrated foods are?

A

Left in a dehydrated state, like prunes and raisins

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

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8
Q

What does Dehydration do?

A

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

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9
Q

What is Surface Area and why is it important?

A

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

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10
Q

If food is not dried enough what can happen?

A

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

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11
Q

Dehydrators use what for drying?

A

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

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12
Q

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

A

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

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13
Q

What does faster drying mean?

A

Faster drying means less change in food quality

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14
Q

What is a Case Hardening?

A

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

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15
Q

Oxygen exposure causes what?

A

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

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16
Q

Can Dehydration denature enzymes?

A

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

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17
Q

What is Pasteurization?

A

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

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18
Q

What is Blanching?

A

Blanching in boiling water is used with vegetables

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19
Q

What is Sulfiting?

A

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

20
Q

What does Sulfiting do?

A

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

21
Q

What is Sulfuring?

A

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

22
Q

What is a disadvantage to Sulfuring?

A

A disadvantage is that some people are allergic to sulfur dioxide

23
Q

What happens in Sulfuring?

A

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

24
Q

What are some advantages of Sulfuring

A

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

25
Q

What are the advantages of Sulfuring and Sulfiting?

A

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

26
Q

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

A
  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
27
Q

What is Tray Drying (Dehydration Method)?

A

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)

28
Q

What is Belt Drying (Dehydration Methods)?

A

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)

29
Q

What is Drum Drying (Dehydration Method)?

A

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

30
Q

What is Spray Drying (Dehydration Method)?

A

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)
31
Q

What is Vacuum Drying (Dehydration Methods)?

A

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
32
Q

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

A

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
33
Q

What is Oven Drying (Home-Dried Foods)?

A

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
34
Q

Foods that are about to undergo dehydration should be what?

A

Should be clean and free from blemishes

  • Drying should take place right after harvest
  • Trays need to be rotated every couple of hours
35
Q

Where should Home-dried foods be stored?

A

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

36
Q

What is Rehydration?

A

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
37
Q

Why are some foods undergoing rehydration dusted with starch?

A

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

38
Q

What is Food Concentration?

A

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

39
Q

What are Concentrates?

A

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

40
Q

What are the benefits of Concentrates?

A

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

41
Q

Some Problems with concentrates are?

A

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

42
Q

Low-acid foods require what?

A

Low-acid foods require additional preservation methods to destroy pathogens

43
Q

What is the Open Kettle (Concentration Methods)?

A

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

44
Q

What is the Heat Evaporation Method (Concentration Method)?

A

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
45
Q

What is Vacuum Evaporation (Concentration Method)?

A

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

46
Q

What is the Filtration Method?

A

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

47
Q

What are Intermediate-Moisture foods?

A

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

FDSC 200 (15 decks)

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