food science Flashcards
name 5 reasons why food is cooked?
-make it safe to eat
-improve shelf life
-develop flavours
-improve texture
-varies diet
how does cooking food make it safe to eat?
-kills bacteria = abouve 75 degrees
-prevents you from getting food poisoning etc
how does cooking food improve shelf life?
give an example x
-cookes to high temps to destroy mould & bacteria
-milk = pasteurised (heated to 72 degrees form 15 secs) = preseves it for longer
how does cooking food develop flavours?
-chemical reactions occur = caramilastion - makes food sweeter
-brasing/roasting = allows meat to absorb flavours of stock,veg etc
-crisper
how does cooking food improve textures?
-easier to chew, swallow & digest
-gelatanisation = thickens starchy soucces & starch swells in rice and pasta = become soft
-egg whites = protein coagualtes = becomes firm
(from proteins denaturing and joining together
name the 3 ways heat can be transferred when cooking?
conduction
convection
radiation
how does conduction transfer heat?
-solid (pan) placed on hob
-causes particles in pan to vibrate, more heat energy = more KE = more collisions, collide w near by particles e.g food
transfers heat to food by vibrations
how is heat transfered by convection? (through gasses/ liquids)
-pan [heat transfer to pan = conduction] on hob = warm water rises & cold water simks this repeats creating a CONVECTION CURRENT = after abit heats the food
SAME OCCURS W HOT AIR IN OVENS
how is heat energy transfered through radiaition?
-waves of radioton pass through food = absorbes - heats food
e.g toasters and microwaves
how do proteins de nature name 3 ways?
mechanical agitation = whisking etc
heat
acid
how do proteins de nature?
-chemical bonds break
-protein unravell
how do denatured proeins coagulate?
-denatured proetins join together , water gets trapped betwen protein molecules
using the e.g of egg whites what changes occur from coagulation?
-firmer texture
-white colour
-
what happens if food is overcooked?
protein molecules tighten = water forced out = hard and chewy eww
how are foams formed?
using egg whites
-proteins in whites denature[form mechanical agiatation -whisking] casusing them to stretch = air becomes trapped
-proteins coagulate
=gas in liquid foam
what happens if you over whisks
-proteins break = air released = foam colappses
why does gluten need kneading?
-develop strands, longer, stronger, strechier
what happens to gluten (coiled for elasitity) at high tmeps?
-coagulate, dough stays stretch , ligh airy texture
expalin the process off gelatinasation?
60 degrees - starch molecules start to swell (absorbs water)
80 degrees - starch molecules burst relaesing starch into liquid
100 degrees = strach evenly distributed & gelatinisation complete
whats is dextrinsioation?
what does it produce?
-breaks down starch molecules into simple sugar [heat] = dextrins
affect of dextriniasation?
-browner colour
-crispier texture
what is caramlaisation?
sugar breaks down - sugar goes brown & chnages flavour
affects of caramalisation?
-adds sweetness and brown colour
what are the processes of sugar?
-very sweet and runny
-smooth caramel
-cools = becomes hard brittle candy
what is aeration?
e.gs?
when fats e.g butter is beaten with sugar
-light, fluffy texture
-whisking egg whites
whats shortnening?
-gives food crumbly texture
-rub fat into flour
-flour gives fat waterproof coating
-prevents long gluten strands forming
=short crumbly texture
what does plasticty mean?
abilty to spread and shape foods
more placsticity = easier to spread
what do fats contain hic allws plasiticty?
triglycerides
what type of fat has a more plasticty?
unsaturated = liquid at room temp(healthier)
advantages of plasiticy?
-decorating cakes
-rubbing in fat
-spreading butter oon toast
-cream cheese on crackers
name to ends of emulsifiers? (needed to keep water and oil together)
hydrophilic-attacted to water
hydrophobic-repulsed by water
what happens when u add an emulsier to water & oil?
hydrophilic bonds to water
hydrophobic bonds to oil = holds mixture together in a stable emulsion
what emulsifier does egg yolks contain?
lecithin
name an exampple of an emulsion?
sauces =hollandaise sauce
how is hollandaise sauce made?
-melt buuter
-mix yolk and lemon jucie - heat gently
-add together and whisk
what happens if u add fat to fast in emulsiation?
-wont bond to hydrophilic/phobic ends xx
how does bioligical rasing agent yeast work?
e.g in bread the process of FERMENTATION occurs - yeast reales carbon dioxide & alchol
-when heated CO2 mkaes bread rise
name a chmical raising agent?
how does it work?
- bicarbonate of soda = rleases CO2 bubbles to make food rise [heat needed for reaction to occur]
con of BOS?
-alkaili = leavs soapy tatse
-need to be made in strong things
e.g choclate cake
pros of using baking powder?
-mix of cream of tatar(acid) and BOS(base) = neutralisation reaction
how does steam make food rise?
-crossiants and shoux pastry
-when bakes
-steam rises
-water evaporates
when cooking crossiabts why cant u open the oven?
-cold air = makes thing sink
name 5 methos we can phycally add air to food?
-folding cake traps air or pastry air in between layers is trapped
-beating (vigouros)
-whisking
-seiving
-creaming & rubbing
