Phase changes and Food Classification Groupings

Question 1

1. Explain transitions of phases in food and cooking

Answer 1

• Water as gas
• Water as liquid
• Water as solid

LEMON MERENGUE PIE EXAMPLE:
Within a Lemon merengue pie the phase transitions seen are:
1. Liquid to gas e.g. bringing water to a boil
2. Liquid to solid – e.g. cooling of the filling (a starch paste to be covered further later this semester)
3. Solid to liquid – e.g. heating of sugar in water
4. Liquid to solid – e.g. baking the egg white foam

Question 2

2. Describe heat transfer, what affects it and which type occurs in various cooking techniques

Answer 2

the movement of heat, which is a form of energy, from one area to another due to a temperature difference

3 COMPONENTS:
1. FOOD
2. HEAT SOURCE (e.g. gas on stove)
3. MEDIUM FOR WICH HEAT IS TRANSFERRED TO FOOD (e.g. saucepan)

5 ways heat is transferred to food:
1. Conduction
2. Convection
3. Radiation
4. Induction
5. Dielectric heating

Question 3

2. what is conduction

Answer 3

e.g. eggs being cooked in fry pan above heat source)
- Heat source transfers heat through a medium directly to the food
- Thermal energy is transferred to the outer surface of the food
- Molecules start to vibrate
- Adjacent molecules themselves begin to vibrate
- Heat passes through via direct contact

Question 4

2. Convection

Answer 4

• A heat source distributes thermal energy through movement
• Warmer gases (usually air) or liquids (usually oil or water) close to the heat source move towards cooler gases or liquids further from the heat source
• This creates a circular movement of heat

Question 5

2. Radiation

Answer 5

(conventional ovens, toasters, grills)
Heat is transferred directly between objects without an intervening medium
- Food absorbs electromagnetic waves which are emitted by a heat source
- The outer surface of the food increases in temperature as molecule begin to vibrate
- Heat is transferred through the remainder of the food by conduction

Question 6

2. Induction

Answer 6

• Use of electromagnetic forces for heat generation
• A magnetic field causes rapid vibration of the transfer medium’s molecules * Heat is then created by movement
• Advantage is safety, efficient (less exposed to heat). Disadvantage (needs to contain stailnless theme)

Question 7

5. Dielectric heating

Answer 7

e.g. microwave

• Microwave electromagnetic radiation is used to generate heat directly within the food
• The food must have polar molecules
• Polar molecule interact under the influence of oscillating microwaves
• Polar molecules in food vibrate and distribute heat which is generated by intermolecular friction

Question 8

what are the influences on heat transfer

Answer 8

• Temperature difference
• Food surface area
• Food thickness
• Food specific heat capacity
• Food thermal conductivity
• Cooking material specific heat capacity
• Cooking material thermal conductivity
• Cooking material thermal diffusivity
• Cooking material emissivity

Question 9

5. Describe kitchen equipment used to aid transitions in food.

Answer 9

aluminium, copper, stainless steel, cast iron, glass, corning wave

Question 10

6 .Define a food commodity and staple crop

Answer 10

Commodity – a raw material or primary agricultural product that can be bought or sold
The Food and Agricultural Organization of the United Nations has grouped food commodities as:
* Cereals and cereal products
* Roots and tubers
* Sugar crops and sweeteners
* Pulses
* Nuts
* Oil bearing crops
* Vegetables
* Fruits
* Spices
* Vegetable and animal oils and fats
* Beverages
* Products from slaughtered animals
* Products from live animals
Staple foods/crops – One that is eaten regularly and in such quantities as to constitute the dominant part of the diet and that supplies a major proportion of energy and nutrient needs (Stirling and Crawford 2017; FAO of the UN, 1995)
What do you think are the staple foods of Australia??
Wheat, dairy products, meat, vegetables and potatoes, rice and pasta, fruit. – eated regularly

Question 11

7. Identify key food groupings, including a wide range of food products contained in each group

Answer 11

1) Vegetables and legumes/beans;
2) Fruit;
3) Grain (cereal) foods, mostly wholegrain and/or high cereal fibre varieties;
4) Lean meats and poultry, fish, eggs, tofu, nuts and seeds and legumes/beans; and
5) Milk, yoghurt, cheese and/or other alternatives, mostly reduced fa

grains and cereals, fruits, vegetables, milk, yoghurt and cheese, meat, poultry, fish, egg and alternatives, legumes, nuts, fats and oils, alcoholic beverages, herbs and spices