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Changing Properties - DONE FOR EVER! - Coggle Diagram
Changing Properties
- DONE FOR EVER!
Proteins
Denature during prep & cooking
proteins have a complex structure
when food is cooked proteins denature - chemical bonds holding structure break down
proteins unravel - shape changes - mostly irreversible
denatured in different ways:
physical agitation (whisking, beating)
change in temp (heat)
acids (lemon juice)
Denatured proteins coagulate
once denatured - collide with other molecules and coagulate (join together)
during the process - water becomes trapped between the molecules
coagulation changes appearance & texture - e.g. egg white turns from a see-through liquid into a white solid - steak becomes brown, firmer, easier to eat as you cook it
if food is overcooked & coagulation happens too much proteins tighten - forces water out and makes it dry, rubbery, chewy
Foams - when air is trapped
foams, e.g. choc mousse, whipped cream - forms when gas trapped inside liquid (aeration)
liquids containing proteins are agitated (egg whites whisked) proteins inside liquid denature - causes them to stretch & air is trapped in liquid
when proteins coagulate - air is trapped - creating a foam
over whisking causes new protein bonds to break - air escapes & collapses
some foams form a solid structure when cooked (egg whites into meringues)
gluten - doughs stretch & rise
gluten is a protein found in wheat flours
formed when water mixed with flour - makes dough - found in foods such as bread, pasta, cakes
molecules of gluten coiled - able to stretch & bend - gives dough elasticity
doughs need to be kneaded to work gluten - gluten strands get longer, stronger & strechier
when reaches high temp - gluten coagulates - dough stays stretched - cooked bread light, airy texture
carbohydrates
starch geltatinisation - thick liquids
geltatinisation helps thicken foods containing starch - sauces, custards & gravies
when starch granules first mixed with liquid - become suspended - if you don't stir granules will sink
when granules heated bonds between starch molecules break - allows water molecules to enter - water absorbed starch granules swell in size & soften
between 62degrees & 80 starch granules burst open & release starch into liquid
this release of starch causes liquid to thicken - how thick depends on ratio of starch to liquid - more starch the thicker
when cools liquid solidifies & solid gel formed - useful for making set desserts (custard & lemon pie filling)
geltatinisation happens when starchy foods (pasta & rice) are cooked - they swell, release starch into water
Dextrinisation - starch exposed to dry heat
this breakdown Dextrinisation - gives food browner colour & crispier texture & different taste
longer food is cooked - more starch converted into dextrin & darker & crispier food becomes
when starchy foods e.g. bread are cooked with dry heat (toasting) starch molecules in food break down into smaller molecules (dextrins)
Caramelisation
sugar molecules break down when reach high temp - causes sugar to turn brown & change flavour
sugar goes through various stages:
first liquid is runny & very sweet
over time becomes like a smooth caramel
eventually becomes harder & as it cools becomes more like a candy
caramelised sugar can burn v quickly - turns black, brittle & bitter taste
to avoid - water added at start of heating
caramelisation gives desserters extra sweetness (crème brulee)
savory foods containing sugar can caramelise (onion) - sugars in food broken down & released - turns food brown & adds sweetness
Fats & Oils
Aeration - incorporation of air
when fats (butter) are beaten with air (called creaming) air is trapped in mixture - mixture is fluffier & lighter in colour
aeration gives cake spongy & light texture when cooked
foods can be aerated in many different ways (whisking egg whites, beating ingredients with spoon)
Shortening - crumbly texture
when fat is rubbed into flour - cover flour particles with fat - waterproof coating
coating prevents long gluten molecules forming when water is added
means dough can't become stretchy & baked goods (shortbread) keeps short - firm crumbly texture
shortening used to make filled pies - good cos base doesn't rise & forms solid case
some fats called 'shortening' have 100% fat content - helps to stop gluten formation & prevents steam from raising food
Plasticity - ability to spread & shape
fats have plasticity - able to spread them
possible cos fats contain mixture of different triglycerides (3 fatty acids together) - all melt at different temps - fats gradually soften over range of temps rather than melting at once.
more plasticity a fat has - easier to spread
unsaturated fats normally soft or liquid at room temp - saturated fats normally solid - more unsaturated fatty acids a fat or oil contains - more plasticity fat or oil will have
plasticity is useful:
decorating cake with buttercream
rubbing fat into flour to make shortened dough
putting cream cheese on crackers
some veg fat spreads are marketed as 'easy to spread' - contain a mixture of triglycerides with low melting points - can spread as soon as you take out of fridge
Fats & oils continued
Emulsification - keeps oil & water together
emulsions formed when oily & watery liquids shaken together
Milk, margarine & mayonnaise are all examples
usually, oil & water don't mix - so emulsions separate out again unless you keep shaking/stirring together - or use an emulsifier
molecules in an emulsifier have 2 different ends - one is hydrophilic (attracted to water) and other is hydrophobic (repulsed by water)
when you add emulsifier - water molecules bond to hydrophilic side & oil molecules bond to hydrophobic side - holds oil & water together in stable condition - prevents separation
emulsions can either be oil-in-water (milk, mayonnaise, salad dressings) or water-in-oil (margarine, butter)
egg yolks contain lecithin - used as the emulsifier in margarine & mayonnaise
Emulsions for sauces & salad dressings
often used as sauces & salad dressings
Hollandaise sauce is another example of an emulsion sauce - made from butter, water egg yolks (lecithin acts as emulsifier) & lemon juice for flavour
Steps to make Hollandaise sauce:
Melt butter in a pan
mix egg yolks & lemon juice in a bowl
gently warm mixture by placing bowl over a pan of simmering water
slowly add melted butter to mixture - constantly whisking
keep whisking sauce until it is all mixed together smoothly
when making any oil-in-water emulsion (sauce or dressing) important to add liquid and emulsifier first, before v slowly adding oil/fat while mixing viguorosly