Food Science (Advanced Info) Flashcards
What are the three phases in an emulsion?
Continuous phase
Dispersed phase
Interphase
Name the two parts to an emulsifier:
Hydrophilic
Hydrophobic
What are the three types of food mixtures?
Sols
Colloids
Suspensions
The three types of colloids:
Foams
Gels
Emulsions
What happens to a cake when it is in the oven?
- The air expands from the air bubbles produced by the raising agent
- Water turns into steam which pushes the dough up
- Eggs coagulate at 62 C
- Gluten sets at 70 C
- Starch in the flour gelatinises
- Maillard reaction occurs - cake goes golden brown
Why is food cooked?
Makes food safe to eat
Makes the food more digestible and palatable (pleasant to taste)
Makes the food less bulky
The flavour is improved
What are the three basic methods of heat transfer?
Conduction
Convection
Radiation
How is heat transferred in conduction?
Heat is transferred by contact with heat
How is heat transferred in radiation?
Direct rays pass from the heat source to the food
How is heat transferred in convection?
Heat moves through the convection currents.
The hot air rises and cool air falls
Methods of cooking for conduction
Boiling, simmering, blanching, poaching, baking, frying, roasting
Methods of cooking for radiation
Barbecuing
Grilling
Microwaving
Methods of cooking for convection
Baking, boiling, simmering, blanching
What are the factors that influence the method of cooking used?
The type of food being cooked How much time is available The needs of the consumer The skill of the cook Consumer choice
What are the moist heat cooking methods?
Boiling, simmering, poaching and steaming
What are the dry heat cooking methods?
Baking, roasting, frying, stir frying
Describe boiling
Boiling uses large amounts of rapidly bubbling liquid (100oC) to cook foods
Heat is transferred through both conduction and convection
Describe simmering
The foods are cooked in hot liquid (85-99oC), but require gentler treatment than boiling to prevent food such as fish or meat from toughening
Describe poaching
Similar to simmering but with a lower temperature (below 85oC)
Describe blanching
Food is cooked and then cooled quickly to stop the cooking process.
This is achieved by putting the food into iced water
Describe steaming
The food does not come into contact with the boiling water, but it is cooked by the steam that is rising from the boiling water.
It is the convection currents that transfer heat to the food
Describe baking
When food is baked it mainly uses dry heat.
In gas ovens, the top is usually the hottest because the warm air rises to the top of the oven by convection
Describe roasting
Food is cooked by dry heat. A small amount of fat is also used to prevent the food from drying out and to develop the flavour
Heat is transferred to the foods by conduction
Describe braising
Usually used to cook meat
The meat is first browned in a pan using a small amount of fat.
It is then out in a container with some liquid and covered with a lid
Describe a casserole
Using this method, food is cooked in a small amount of liquid that simmers.
A casserole is cooked in a container with a tight fitting lid so the liquid does not evaporate.
The liquid is served with the food
Describe frying
Heat is transferred to the food by conduction through the pan and by convection from the hot fat
What are the four different types of frying?
Dry frying
Shallow frying/pan frying
Stir frying
Deep frying
Describe dry frying
Some foods can be fried without any fat being added to the pan
Describe shallow frying
This is when foods are cooked in a shallow layer of hot fat or oil.
It is a very quick method of cooking, so not suitable for tough cuts of meat
Describe stir frying
This method originated from East Asia.
Small pieces of finely chopped food are cooked in a wok.
The temperature of the oil is high and the food is constantly moved around the pan
Describe deep frying
When food is deep-fried, it is completely covered in fat during the frying process
Describe grilling
This is a quick method of cooking where heat is conducted through radiation
When the foods are cooked, the surface is quickly sealed due to the dry heat.
It also must be turned often to ensure even cooking
Describe microwaving
Microwave ovens work by:
The microwaves penetrating into the food and causing the molecules in the food to vibrate - this is by radiation
The molecules causing friction when they vibrate against each other, which produces heat - this is conduction
The water molecules continue to vibrate when food comes out the microwave, which generates heat, allowing the cooking process to be completed. During this time, the centre of the food will gain than lose temperature
Advantages of boiling
A quick method of cooking as the transfer of heat is rapid
Food is not likely to burn
A simple method of cooking
Advantages of steaming
Food cooked by this method is usually light in texture and therefore easy to digest
Steaming retains the natural vitamins found in each food
Advantages of grilling
Quick method of cooking, reduces energy costs
Advantages of frying
A quick method of cooking
Food is usually attractive in colour - golden brown
Advantages of microwaving
Food is cooked very quickly Useful for people with busy lifestyles Bright colours are usually retained Very useful for defrosting frozen foods Less destruction of heat sensitive vitamins Less loss of water soluble vitamins
Disadvantages of boiling
Food may disintegrate if it is not carefully timed
Some flavour from the foods will leach into the water
Water-soluble vitamins may be lost
Disadvantages of steaming
Depending on the product, it can take a long time
Care with timings must be taken so that delicate foods such as fish are not overcooked
Disadvantages of grilling
Not suitable for tough cuts of meat
Careful timing of cooking is needed so that foods are not overcooked or undercooked
Disadvantages of frying
Fats need straining and changing regularly
Fried food is more difficult to digest
Great care has to be taken from a safety perspective when frying food
Heat sensitive vitamins are destroyed
This method of cooking increases our fat intake
Disadvantages of microwaving
Careful timing is required as foods can easily be overcooked
The flavours may not develop in the food due to the rapid cooking
How is protein affected by cooking processes?
The amount of protein in the food is not affected by the method of cooking
How are carbohydrates affected by cooking processes?
Fibre (NSP) is softened, particularly when cooked by moist methods of cooking
Starch may be reduced when food is cooked in water as it dissolves in the liquid
How is fat affected by cooking processes?
The fat content of some foods may be reduced when cooking e.g. grilling will allow the fat to drain out of the food
Cooking food in fat will increase the fat content and the calorie content
How are fat soluble vitamins affected by cooking processes?
Most fat soluble vitamins are not affected by cooking processes except from vitamin A which disintegrates in frying when high temperatures are used
How is vitamin B1 affected by cooking processes?
Soluble in water so it is lost if liquid is drained
Easily destroyed by heat
How is vitamin B2 affected by cooking processes?
Soluble in water, so lost if liquid is drained
Destroyed by heat in the presence of an alkali (e.g. bicarbonate of soda)
How is vitamin B3 affected by cooking processes?
Soluble in water so it is lost if liquid is drained
More resistant to heat than any of the other B vitamins
How is folic acid affected by cooking processes?
Less sensitive to heat than other vitamins but is destroyed if food is reheated or kept warm for a long time
How is vitamin B12 affected by cooking processes?
Soluble in water so it is lost if liquid is drained
How is vitamin C affected by cooking processes?
Destroyed by moist and dry heat
Dissolves in water so cooking methods which use the minimum amount of water should be chosen
How are minerals affected by cooking processes?
Generally the nutritional value of minerals is not affected by normal cooking processes
How do cooking methods/processes improve the sensory properties of food?
Makes them easier to chew, swallow and digest
Some methods such as grilling improve the colour of food
Some foods cannot be eaten raw so must be cooked
The flavour of food is often developed by the method of cooking chosen
What functions can an ingredient have in a recipe?
To thicken
To aerate
To coagulate
To add nutritional value
What is a colloidal structure?
When two substances are forcibly mixed together
How is starch used in recipes?
It is mainly used to thicken mixtures
How is flour used in recipes?
It is often used to bulk out a recipe and forms the main structure of many products, including cakes, bread, pastry and biscuits
What happens when moist heat is applied to sugar?
The sugar melts and becomes syrup.
At 154oC, the sugar starts to change colour - this process is called caramelisation. The longer the sugar is heated, the deeper the colour of the caramel and the harder it will set when it is cooked
What is the effect of dry heat on sugar?
Sugars will also caramelise when dry heat is applied to them.
When they are mixed with other products such as eggs and flour, browning occurs in the dish.
This is known as the Maillard Reaction
What is the Maillard Reaction?
This happens when foods containing proteins and carbohydrates are cooked by dry methods
How is sugar used to aerate a dish?
Aerating means adding air to mixtures
When sugar is beaten with a fat or with egg, air is added to the mixture.
This helps to make cakes rise and gives them a light texture
What are the different functional properties of fats and oils?
Plasticity Shortening Aeration Emulsions Flavour and moisture
What is plasticity?
Plasticity is the ability to be shaped and spread with light pressure.
This is useful for fats as not all fats melt at the same temperature, so some products are designed to have a lower melting point
What is shortening?
Shortening is when fat is used to give the flour a waterproof coating and prevent the gluten in the flour from developing.
This allows the finished product to have a short, crumbly texture
What is aeration when fat is used?
When a fat and sugar are creamed together, air becomes trapped.
When the product is heated, the air will expand, causing the mixture to rise
What are emulsions?
An emulsion is formed when oil and a liquid are mixed together.
Usually these separate when left to stand, so an emulsifier is sometimes added to prevent this
What is denaturation?
Caused by adding acids to protein e.g. tenderising meat
And by mechanical action e.g. whisking egg whites
What happens to meat when it is cooked?
The muscle fibres begin to coagulate between 40-60oC
After 60oC, the fibres in the meat shrinks and the juice in the meat is squeezed out
The collagen in the fibres turns to gelatine to make it easier to digest
The meat changed colour from red to brown with the effect of dry heat
What happens to fish when it is cooked?
The muscles in the fish shrink as they are very short and there is only a small amount of connective tissue
If cooked for too long, the fibres become toguh
What happens to eggs when they are cooked?
The egg white begins to coagulate at 60oC. The egg white will change from an opaque colour to a white colour
The egg yolk begins to coagulate at 70oC
What is syneresis?
When an egg is heated too quickly, the liquid from the egg separates out and the protein becomes tough.
Sometimes seen when cooking scrambled eggs
What happens to milk as it is heated?
A skin forms on the top layer, which is the proteins coagulating
What is aeration when proteins are used?
The process of trapping air in a mixture.
When egg whites are whisked, the protein, albumin, is stretched and traps the air.
If left to stand, they will eventually collapse and become a liquid once again
What are the names of the proteins found in wheat that form gluten?
Gliadin
Glutenin
What is gluten formation?
When the two proteins in flour combine with water to form gluten.
This gluten is then developed when it is being kneaded
How is vinegar used in food products?
It is used to:
Tenderise meat, as the acid softens the meat tissues
Provide a soft texture - if a small amount of vinegar is added to a meringue mixture, the centre of the meringue remains soft and similar to texture to marshmallows
How is lemon juice used in food products?
It prevents foods from going brown - it improves the appearance of the food
It sets mixtures that contain protein e.g. cheesecakes
What is enzymic browning?
The reaction between a food product and oxygen, resulting in a brown colour
What is oxidisation?
Occurs when fruit and veg are cut and the cells are exposed to air
What is a raising agent?
A raising agent is added to a cake or bread mixture to give lightness to it
The lightness is based on the principle that gases expand when heated
What gases are used in raising agents?
Air
Carbon dioxide
Water vapour
What is yeast?
Yeast is a living organisms which when given the right conditions, it can break down food to produce carbon dioxide.
What is fermentation?
The process by which yeast breaks down food to produce carbon dioxide and alcohol when given the ideal conditions - food, warmth, moisture and time
What are the different types of raising agents?
Bicarbonate of soda (used alone)
Bicarbonate of soda + acid (cream of tartar)
Baking powder
What happens when too much raising agent is used?
Over-rising, then collapsing giving a sunken cake or sunken fruit
Coarse texture
Poor colour and flavour
What happens when too little raising agent is used?
Lack of volume
Insufficient rising
Shrinkage
How is air incorporated into a mixture?
Sieving flour Rubbing fat into flour Creaming fat and sugar Beating mixtures Folding and rolling (pastry) Adding whisked egg whites
How is steam used as a raising agent?
Steam is produced when products are baked, from the liquid present in the mixture
What products use steam as a raising agent?
Eclairs and choux pastries
Batters
Flaky and puff pastry
What is gelatinisation?
When flour is mixed with a liquid and heated, such as in a sauce, the mixture will thicken.
How does gelatinisation occur?
The starch grains cannot dissolve in the liquid so they form a suspension
As the liquid is heated, the starch grains swell (at 60oC), and as more heat is applied, the starch grains break open, causing the mixture to thicken (at 80oC)
What is dextrinisation?
When dry heat is applied to products, such as when baking bread, it causes the product to brown
Why does dextrinisation occur?
The starch in the flour is changed into a sugar
What is caramelisation?
When the colour of sugar changes from white to brown when heated
How does caramelisation occur?
The sugar melts and becomes syrup
At 154oC, the sugar starts to change colour
The longer the sugar is heated, the deeper the colour of the caramel and the harder it will set when it is cooled
What is acid denaturing?
When acids are used to change the shape and structure of protein foods
E.g. to tenderise meat
How does acid denaturing work?
The acid causes a change in the structure of a protein.
The long chains of amino acids unfold.
When applied to meat, for example, it softens the meat tissues
What is the purpose of the chalazae in an egg?
It holds the yolk in place so it doesn’t fall onto the air sac and dry out
What proteins are present in the connective tissue of meat?
Elastin
Collagen
What proteins are present in the bundles of muscle fibres in meat?
Actin
Myosin
What are the characteristics of tough meat?
Long, muscle fibres Lots of connective tissue Older animals Come from sections of the animal which have been exposed to more activity More flavour Cheaper
What are the characteristics of tender meat?
Short, muscle fibres Little or no connective tissue Younger animals Sections of the animal which have been exposed to little activity Less flavour More expensive
