food science Flashcards
what is convection
transfer of heat through liquids and gases
equipment that cooks with radiation
grill, toaster, microwave
how do microwaves heat food
radiation
• heat energy is transferred by waves of energy hitting food, water molecules absorb the waves which heats them up
heat transfer in an oven
heating element emits radiation, hot air rises and pushes cool air down which creates a convection current, heat then transferred through food by conduction
heat transfers in simmering sauce on a hob
to base of pan by conduction, pan heats sauce at base by conduction, heat transferred through the sauce by convection
benefits of blanching
the cold water preserves colour, texture and vitamins
why is food cooked
- to make it safe to eat - kills pathogenic bacteria and harmful toxins
- improves shelf life - bacteria and mould are destroyed
- develops flavour - chemical reactions change the flavour, cooking can allow different flavours to combine
- improves texture - easier to chew, swallow and digest
- gives variety in the diet
poaching
cooking food in a pan of liquid below boiling point (usually around 80˚C)
food can be poached in a flavoured source to add variety and flavour
- if not, it can lose flavour to the liquid
braising
slowly cooking food in an ovenproof pot with the lid on that contains liquid
- the food is cooked by both simmering and steaming
- helps tenderise big/tough joints of meat
- meat is usually fried to light brown to seal it before braising, helps keep juices in the meat and give a caramelised flavour
- flavours in the pot are absorbed by the meat
pros and cons of baking
+ wide variety of foods
+ crisps and browns outside of the food, which tastes and looks nice
+ quite healthy bc no extra fat is added, and solid fats in the food often leave once baked
- can take a long time
- food can get dried out
- uses a lot of energy, the oven has to stay at a high temp for a long time
pros and cons of grilling
+ food cooks quick at a high temp
+ no fat is added, so fairly healthy
+ fat drips out of the food and the outside becomes golden and crisp
+ grilling on the barbecue can give a popular, smoky flavour
- the high heat makes it difficult to cook evenly
- easy to burn the outside and have the inside still raw
- handling raw and cooked meat on a barbecue can lead to cross-contamination
modern electric ovens
fan assisted/convection ovens
- circulate air
- the food bakes more evenly bc the oven is all at the same temperature
- use less energy - the oven heats quicker and the food cooks quicker
roasting
+ extra fat and high temp - browns and crisps outside but keeps inside moist which is yum
+ fat from roasted meat can be used to cook other foods
+ tasty and moist
+ can produce a rare centre - which lots of people like
- extra fat is added - not super healthy
- takes a long time to cook, uses a lot of energy
pros and cons of dry frying
+ no fats added - healthier
+ can give a more distinct aroma to nuts, seeds and spices
- takes longer - lower temps are needed at the start to melt fats
- can only be used for a small range of foods (should contain natural fat)
proteins denaturing
when food is cooked proteins denature - the chemical bonds holding their structure together break down
it is usually irreversibe
they can denature in several ways:
• physical agitation (whisking, beating, kneading)
• temperature change (heat)
• acids
protein coagulation
(post denaturing)
- protein molecules collide with other protein molecules and coagulate (join together)
- water gets trapped between the protein molecules
- coagulation changes the appearance and texture of food
- overcooking food - coagulation happens too much and the protein tightens, this forces water out of the molecules making it dry and chewy
forming foams
- proteins inside the liquid denature from agitation
- they coagulate and form a foam
- over whisking causes the bonds to break - air escapes and the foam collapses
- some foams can form a solid structure when cooked
gluten
gluten - a protein found in wheat flours
- forms when water is mixed with wheat flour to form a dough
- gluten molecules are coiled - they can stretch and bend which gives doughs elasticity
- kneading doughs works the gluten - causes gluten strands to get longer, stronger and stretchier
- at high temps, gluten coagulates and the dough stays stretched - gives food like bread a well-risen, airy texture
gelatinisation
- when starch granules are first mixed with a liquid they become suspended - without stirring they will sink to the bottom
- heating the granules with water - bonds between starch molecules begin breaking, allowing water to enter. water is absorbed so starch granules swell and soften
- between 62˚C and 80˚C the granules burst open, releasing their starch into the liquid, causing the liquid to thicken
- when it cools, the liquid solidifies and a solid gel is formed
dextrinisation
when starchy foods are cooked with dry heat
• the starch molecules break down into dextrins
caramelisation
sugar molecules break down at high temps causing the sugar to turn brown and change flavour
1) runny and sweet
2) more like a smooth caramel
3) becomes harder and more like a candy as it cools
shortening
- flour particles are coated in fat, giving them a waterproof coating
- the coating prevents long gluten molecules forming when water is added
some fats are called shortening when they have 100% fat content (no water), stopping gluten formation and preventing steam from raising the food
plasticity of fats
- fats contain a mixture of different triglycerides which melt any different temperatures - so they soften over a range of temps vs melting at one
- easy to spread - made of a mixture of triglycerides with low melting points
- the more unsaturated fatty acids that a fat/oil contains, the more plasticity that it’ll have
emulsifiers
emulsions are formed when oily and watery liquids are shaken together but won’t become stable without an emulsifier
• molecules in an emulsifier have a hydrophilic and hydrophobic end
emulsions can be oil-in-water (milk, mayonnaise, dressings)
or water-in-oil (margarine, butter)
chemical raising agent
bicarbonate of soda
- breaks down to form CO2 bubbles when heated, these expand to make the mixture rise
- alkaline taste, needs to be used with a strong flavour to mask it (chocolate cake)
baking powder = a mix of bicarbonate of soda and cream of tartar,
• a neutralisation reaction takes place when baking powder is heated so it doesn’t taste weird
self-raising flours - contain a mix of plain flour and baking powder
biological raising agent
yeast
- it’s a microorganism that causes fermentation - releasing CO2 and alcohol
- doughs with yeast are often proved to allow fermentation
- fermentation stops during baking as the yeast is killed by the heat
- the CO2 expands during baking, causing further rise
mechanical raising agents
folding cake mixture folding pastry doughs beating sieving creaming
