Food science Flashcards
What does it mean when proteins denature?
This means the chemical bonds that hold their structure together break down
The proteins unravel and their shape changes
Proteins can be denature by:
- physical agitation
- changes in temperatures
- acids
What does it mean when protein molecules coagulate?
Protein molecules collide with other protein molecules and coagulate
Water gets trapped between the protein molecules
Changes appearance and texture
Overcooking-forces water out of molecules
How are foams formed?
When gas becomes trapped (aeration) inside liquid
When liquids containing proteins are agitated, proteins denature and stretch and air gets trapped in the liquid
When the proteins coagulate, this air becomes trapped, forming a foam
Over-whisking causes these new bonds to break-air escapes and the foam collapses
What is gluten?
Protein found in wheat flours
What is starch gelatinisation?
- Helps to thicken foods that contain starch
- Starch granules mix with liquid and become suspended in it
- When heated, bonds will break allowing water molecules to enter
- More water—->swell in size and soften
- When it gets hot enough, the granules burst open and release their starch into the liquid
- When cooled, it forms a solid gel
What is dextrinization?
- Occurs when starch is exposed to dry heat
- Starch molecules break down into smaller molecules called dextrins
-Gives food a browner colour and crispier texture and different taste
How does sugar caramelise when heated?
-Sugar molecules break down (brown and change flavour)
- First, liquids is very runny and sweet
- Time passes, smooth caramel
- Turns harder, more like candy
What is shortening?
- Flour has waterproof coating (fat)
- Prevents long gluten molecules from forming
- Dough cannot become strecthy (firm and crumbly)
Why do fats have plasticity?
-Mixture of triglycerides that all melt at different temps (gradually soften over a range of temperatures)
What are emulsifiers and what do they do?
Oil and water don’t mix so you use an emulsifier to keep them together
Molecules in an emulsifier have an hydrophilic end and an hydrophobic end
Water bonds to the hydrophilic end and oil bonds to the hydrophobic end which holds them together in a stable emulsion
Why do we cook food?
- To make it safe to eat
- To develop flavour
- To improve shelf life
- To improve texture
- To give variety in the diet
What is conduction?
Conduction is the transfer of heat energy through the vibration of particles
In a solid, the particles are held tightly together. So when one particle vibrates, it bumps into other particles nearby and quickly passes the vibrations on
When a pan is placed on a hob, heat energy from the hob causes particles in the pan to vibrate more and gain heat energy
When these particles collide with nearby particles, they pass some of their extra heat energy on to them
This process continues throughout the pan until the heat has passed all the way through
When food is placed into the hot pan, heat energy is transferred from the particles in the pan to the particles in the food in a similar way until the food is cooked
What is convection?
Convection is the transfer of heat energy through gases or liquids
When you heat up a liquid, the liquid near the heat source warms up faster
The warmer liquid rises above its colder surroundings-like a hot air balloon does
As the warm liquid rises, colder liquid takes its place
The colder liquid is heated and when it starts to rise, colder liquid takes its place
As this process continues, you end up with a circulation of fluid (convection currents)-after a while, this circulation of heat results in the whole fluid being heated
Convection also occurs in ovens-hot air rises and cooler air falls in the same way
What is radiation?
Radiation is the transfer of heat energy through waves of radiation
No direct contact between the heat source and food
Grills and toasters
They emit waves of radiation- when these waves reach the food, they are absorbed and heat the food up
How does boiling work?
Cook food by heating it in a pan of boiling liquid, usually water
Harsh method of cooking-can’t be used on delicate foods
Healthy way to cook as no fat is added however if veg is boiled for too long, colour, flavour and water-soluble vitamins are lost in the water
Not as attractive/boiling as food cooked by methods like roasting
Less energy
Heat is transferred by conduction (pan to water to food) and convection (liquid)
How does steaming work?
Steaming means cooking food with steam from boiling water or stock
No fat is added and veg can keep more of their taste, texture, colour and nutrients
Gentle way to cook (suitable for delicate food like fish but not for tough meats)
Conduction (pan to water and through to food) and convection (through the steam)
How does blanching work?
Part cooking food in boiling water for a very short time before putting it in cold (or iced) water
The cold water stops the cooking process-helps preserve colour, texture and vitamins
Removes harsh flavours (onions)
Can make it easier to remove skins (almonds and tomatoes)
Can be used to prepare food for freezing
How does simmering work?
Is like boiling but more gentle as temp is slightly lower than boiling point
Common cooking method for soups and curries
Simmering preserves more nutrients than boiling
How does poaching work?
Cooking food in a pan of liquid below boiling point
Gentle way to cook and keeps food tender
Lowers nutritional content and tastiness of food
Conduction and convection
How does braising work?
Slowly cooking food in an ovenproof pot that has a lid on and contains liquid (water, stock or wine)
Simmering and steaming
Good for big or tough joints of meat-tenderises it
Meat is lightly fried beforehand to brown and seal it to keep juices inside the meat and gives it a caramelised flavour
Conduction and convection
How does stir-frying work?
Tends to be done in wok with a small amount of oil, making is pretty healthy
Food cooks very quickly and needs to be moved around quickly
Vegetables keep more of their nutrients
How does shallow frying work?
Frying pan coated in a medium amount of fat or oil
Less healthy since there is more fat
Crispy texture
What are the advantages and disadvantages of baking?
A wide variety of food can be baked
The outside of the food browns and crisps up, which looks and tastes nice
No extra fat is added so its quite healthy
Baking food can take a long time
Food can become dried out
It uses a lot of energy
What are the advantages and disadvantages of grilling?
Radiation (heat from grill/ hot coals if bbqing) or conduction (griddle pan)
Food cooks quickly
No extra fat
Can have crispy texture and looks nice
Smoky flavour (very popular)
Makes it hard for food to cook quickly
Easy to burn but the inside of food is still raw
Risk of cross contamination
What are the advantages and disadvantages of roasting?
Extra fat and a high temp helps to brown and crisp the outside of food, which looks and tastes delicious
The fat from roasted meat can be used to cook other food
Roasted food can be tasty and moist
Roasting can cause a rare centre which some people may like
Extra fat is added (unhealthy)
Needs long time and lots of energy
What are the advantages and disadvantages of dry frying?
No extra fats or oils are added making the method healthier
Distinct aroma can be attained
Longer time needed due to lower temps needed at the start
Can only be used for a small range of foods
Explain how heat energy is transferred when grilling halloumi
Heat energy is transferred directly from the grill to the halloumi by waves of radiation which are absorbed by the halloumi and heat it up
Explain how heat energy is transferred when cooking a pan of soup on the hob
Heat energy is transferred from the hob to the pan and the soup by conduction
as particles in the hob and pan vibrate and transfer heat energy (pass on their vibrations by colliding with other particles) through the pan and to the soup
Heat energy is then transferred through the soup by convection as convection currents circulate warmer soup around the pan until all the soup is hot and simmering
Boiling and steaming are common methods of cooking carrots
Evaluate which of these methods (boiling or steaming) would be better to cook finely diced carrots
Boiling:
Boiling is quicker
Boiling is a harsh methods that could break up the carrots
The carrots are diced so there’s more contact with the water which increases the risk of the carrots becoming too soft, losing their flavour and their water-soluble vitamins
