Section 3 Flashcards
Why a food cooked
To make it safe to eat-to kill toxins in food that are killed by heat
To improve shelf life-when foods are cooked it destroys bacteria and mould
To develop flavours-chemical reactions take place during cooking thag change flavour of the food eg carameliseation
To improve texture -make it easier to show chew swallow and digest food,some foods are tenderised or softer Ed when eaten
Water based cooking
Boiling-harsh method of cooking as it breaks up delicate foods,healthy as no fats are invloved
Steaming- gentle method,no fat is added due to no direct contact with water
Simmering-preserves more buried ts when boiling
Blanching-helps remove harsh flavours in food and stop food from further cooking helping preserve flavours
Water based and fat based cooking methods
Braising-good method for tough joints of meat it helps to tenderise it, mix of simmering and steaming
Stir frying-little oil used ,food cooks quickly so veg keep more nutrients
Shallow frying -medium amount of oil used ,gives crispier texture
Dry methods of cooking
Baking-uses dry heat,
Advantage-healthy as no extra fat is used, wide variety of food can be baked
Disadvantage-foods can dry and take a long time to bake
Grilling-uses dry heat at higher temp
Advantage-cooks quickly and fairly healthy ,give crispy texture
Disadvantage- easy to burn the food,high risk of cross contamination
Roasting-dry heat but at a higher temp
Advantage-extra fat and high temp helps food brown and crisp,produce meats with a rare centre
Disadvantage-not as healthy and takes longer
Changing properties proteins
Proteins denature when cooked they unravel and shape changes-happens when temp is high and acids are used
Coagulation
Once proteins denature the molecules join together and water is trapped inbetween,changing the texture and appearance
Foam
Once protein molecules denture air gets trapped creating a foam
Gluten
Molecules of gluten coil and give elasticity,kneeding these doughs causes the gluten strands to get longer and stretchier
Changing properties carbohydrates
Geletiniseation
Starch granules at 62-80c burts open and release starch into liquid, this causes it to thicken-higher conc of starch the thicker the liquid, when it cools the liquid solidifies used in custard
Dextrinisation-starch molecules break down into dextrins, dextrins gives food browner and crisper texture
Carameliseation-at high temp sugar goes brown and chanhes flavour
Changin properties fats and oils
Aeration-when fats are beaten air becomes trapped,makes the mixture fluffier and lighter
Shortening-give flour a waterproof coating,prevents long gluten molecules forming and steam connot rise the food ,meaning the dough cannot become stretchy and baked goods keeps a short texture,
Plasticity-fats are able to be spread and manipulated due to them having different triglycerides,these all melt at diff temps, so fats gradually softern
Changin properties fat and oil part 2
Emulsification-water and oil don’t mix to overcome this by using an emulsifier,the molecules in an emulsifier have 2 ends one is hydrophilic and hydrophobic this hood the water and oil togther in a stable emulsion prevnting them from separting
Raising agents
Chemical
Bicarbonate of soda breaks down to produce co2 that expand to make mixture rise,has an unpleasant alkaline taste that requires a strong flavour to overpower
Baking powder mixture of bicarb and cream of Tatar,a neutralisestion reaction that when heated gets rid of the soapy taste
Biological
Yeast is a microorganism that anerobically respires to produce ethanol and carbon dioxide ,doughs containing yeast are proved in a warm place this is important as it makes the bread rise and when the bread is cooked the yeast are killed off and no more fermentation takes place and any alcohols produces are evaporated
Steam hot ovens cause steam to evpouarte out of food as it does the steam raises the mixture up(puff pastry and chox pastry
Mechanical
Air can be folded into a mixture in two different ways:folding a mixture causes air to become trapped as the mixture is pour over itself
Beating you mix a mixture to quickly drive air into it
Uses of microorganisms
Yeasts
During fermentation years convert sugars into co2 and ethanol somtimes co2 is left to add fizz to drink
Moulds added to cheese this mould adds a sharp tangy taste
Yogurts bacteria’s ferment lactose and produce lactic acid, this lactic acid acts on the proteins in the milk to thicken it and gives it a sour tangy taste,probiotics are a supplement in some yougurtd and give health benefits
Lactic acid producing bacteria cause the protiejns in the meat to denature and coagulate this forcing water out ,this lack of ph and water makes it harder for pathogenic bacteria to grow
Food spolage
Warm temp,plenty of moisture,right ph,enough time
Some microorganisms can spoil good others produce bacteria that cause food poisoning
How to prevent
Use fridge to change temp, pickle the food to change the food,add salt to remove moisture
High risk foods
Cooked rice, cooked meat, dairy products,
Signs of food spoilage
Fresh meat should have a bright colour and firm
Fish should have clear eyes and a clean smell
Food spoilage part 2
Enzymic ripening
Enzymes in the fruit causes sweetness, colour and texture change
Enzymic browning
When you slice a fruit the oxygen in the air will turn the fruit brown ,the enzymes in the fruit speeds this up
Slowing or stopping an enzyme from working
Adding an acid the change in ph will cause these enzymes to denature
Blanching prepares veg for freezing, freezing slows down the enzymes but not stop them
Moulds and yeast
Waste products from moulds can cause food poisoning
Can be prevented by correctly storing food
Using fridge and freezers
Fridges should be kept 0 to 5 best for chilling high risk foods
Keep food covered to prevent cross contamination
Don’t let’s blood and juices drip
Keep meet on bottom shelf
Freezers should be set for -18
Food should be labelled with frozen date
Defrost meat and poultry through the fridge
Storing food safely
Freeze drying-food is frozen and dehydrated to remove moisture
Canning-food stealer in can or jar and heated to kill bacteria
Vacuum packing-food is placed in bag and vacuum sealed due to some microorganisms not being able to survive without oxygen
Pickling-food plunged in vinegar or brine to ensure the ph is too high for microorganisms
Jam making-fruit is bottled with sugar -high content ensures that bacteria can’t grow
Use by date -products with short life,given as saftey warning and should not be consumed past the date
Best before-products with longer shelf life ,warning about quality rather than health
Preparing food safely
Cross contamination can occur from-other contaminated foods raw meat juices can drip onto other foods
People-poor personal hygiene
Preparing-wash hands tye hair back wear hair net ,sepourate, Rae and cooked foods, wash veg thourougly, use clean equipment
Cooking-cook food at right temp,make sure food is cooked as way through trst temp inside using temp probe,
Serving -serve hot food straight away to keep it above 63’.keep food coverd to prevent contamination
