Food Science Flashcards
Why is food cooked?
- Food is cooked in order to: make it safe to eat (cooking destroys micro-organisms) change raw food to cooked food make it palatable: develop flavours; improve mouthfeel; improve texture; reduce bulk; improve colour help keep quality (extend shelf life) make it easier to digest give variety to diet.
How is food cooked?
- Cooking uses heat to change texture, flavour and colour of food.
- Cooking methods are wet (moist), dry, or fat-based:
- Wet methods are boiling, steaming, stewing, poaching, casseroling and braising.
- Dry methods are baking, roasting and grilling.
- Fat-based methods are frying and stir-frying.
- Pre-cooking methods can improve tenderness and flavour, for example, a marinade for meat or fish.
The selection of a cooking method depends on: * the type of food being cooked the time available * the skill of the cook and the facilities available * the need to achieve desired characteristics, e.g. browning the need to conserve vitamins, e.g. steam rather than boil to prevent loss of vitamins * the desire to improve palatability, which affects the appearance, colour, flavour, texture and smell.
What happens when you microwave something?
** Microwave cooking uses a type of radiation called microwaves, which travel in straight lines and penetrate the food.
**
1. The microwaves vibrate water molecules creating friction, which makes heat. two theal eating
2. Hot spots can occur, so food should be stirred and left to stand to allow the heat to be distributed evenly.
Microwaves alone do not brown or crisp foods.
Cooking Methods
**Water - based
**
* boiling - softens - vegetables, rice
* simmering - tendriese + evaporates - stews,sauces, curry
* poaching - tenderises - fish,chicken, egg
* braising - tenderises,softens - meats, fish, vegetables
Oven
* moist or fat - tenderises - vegetables, joints of meat, potatoes
Dry
* grilling - chars, browns, crisps - bacon,toast, cheese
* baking - browns,crisps - cakes,pastries
* dry frying - browns,crisps - bacon,lardons,chorizo,nuts
* roasting -brown, crisps - roast chicken, potatoes
**Fat - based
**
* deep frying - browns, crisps - battered fish
* shallow frying - sets,browns - eggs,onions
* stir fry - soften, reduces bulk - bean sprouts
How does convection work to transfer heat into food?
- Convection takes place in air (in ovens) or liquids.
- Currents occur as heated air or water. rises and cooler air. or water falls, e.g. boiling water.
How does conduction work to transfer heat to food?
- Food molecules vibrate to transfer heat via conduction. ·
- Heat is transferred by contact of heat source to pan to food, e.g. frying.
How does radiation work to transfer heat into food?
- Heat energy passing in direct lines to the food, que.g. grill to food.
- Energy from microwaves penetrate food to transfer energy.
What is protein desaturation and what can cause protein to be denaturated?
- Denaturation occurs when the structure of amino acids found in protein are altered. They change shape or unfold because chemical bonds are broken.
- Protein in foods can be denatured (altered) by heat, reduction of pH level (more acid), enzymes and mechanical actions. See chart below.
How does heat denature protein?
- Cooking denatures proteins.
- Denaturation occurs when the structure of amino acids found in protein change shape after cooking - the protein molecule uncoils when cooked.
How does pH denature protein?
- pH is the level of acidity or alkalinity in a food.
- pH is measured from 1, which is very acid, to 14, which is very alkaline.
- Reducing the pH by using lemon juice or vinegar in a marinade denatures the protein in foods to make them tender, tasty and moist.
How does enzymes denature proteins?
- Meat tenderisers cause protein denaturation, making meat more tender.
- Enzymic tenderisers are in the form of papain and bromelain. Papain can be found naturally in papaya and bromelain can be found in fresh pineapple.
- Acidic pH from yogurt, buttermilk, vinegar or citrus fruits helps to tenderise fish or meat (marinades).
How does mechanical actions denature proteins?
Whisking egg white denatures the protein by uncoiling and unfolding, e.g. foam formation occurs (gas in liquid).
What is protein coagulation?
- Protein coagulation is a type of protein denaturation.
- Examples of coagulated foods are egg custards and quiches. It causes a change in texture, for example, runny eggs become coagulated (set).
- It usually starts at 60°C and is completed by 70°C.
- It is irreversible and causes loss of solubility.
When does gluten formation occur?
- Gluten formation occurs when water is added to a wheat flour to form a dough.
- Wheat flour contains two proteins, glutenin and gliadin, which combine to form gluten.
- Strong wheat flour for bread making contains more gluten than plain flour.
What is the function of gluten in bread?
- Gluten makes dough stretchy and elastic.
- Salt and kneading help strengthen gluten.
- Gluten forms the structure of a baked loaf of bread.
What is the function of gluten in pastry?
- Rubbing fat into flour makes short gluten strands - the scientific term for this is shortening.
- Gluten forms the structure in baked pastry.
What is the function of gluten in pasta making?
- Gluten in wheat flour helps pasta hold its shape, e.g. fusilli.
- Gluten also makes the pasta dough flexible and increases its ability to hold various shapes.
How to get the right ratios in gelatinisation?
Define: Retrogradation + Synerisis
- A sauce is viscous, which means it can either be poured (e.g. parsley sauce) or used to coat an ingredient (e.g. cauliflower cheese) or to bind other dry ingredients together (e.g. rissoles).
The change in viscosity is due to the ratio of thickening agent to liquid; more starch gives a thicker sauce. The ratio selected changes the consistency of the sauce from runny to thick.
Retrogradation is the deterioration of a starch-based sauce on keeping - this results in shrinkage, drying and cracking.
Synerisis is the loss of fluid from a foam or set mixture, e.g. lemon meringue pie, and in cheese making.
