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neurologyYou need to know

• Food is cooked to make it safe to eat by killing pathogens that can cause food poisoning.
• Food is cooked to develop flavour because heating triggers chemical changes such as caramelisation and Maillard browning.
• Food is cooked to improve texture because heating can soften tough fibres, gelatinise starch and create crisp surfaces.
• Food is cooked to improve shelf life in some foods because heating reduces microbial activity and can inactivate enzymes that cause spoilage.
• Food is cooked to give variety in the diet because one ingredient can produce different dishes when it is prepared and cooked in different ways.
• Preparation and cooking can change the appearance of food by altering its shape, surface finish and size.
• Preparation and cooking can change the colour of food through browning reactions or pigment changes caused by heat.
• Preparation and cooking can change the smell of food because volatile aroma compounds are released or formed during heating.
• Preparation and cooking can change flavour because ingredients may taste sweeter, more savoury or less bitter after cooking.
• Preparation and cooking can change texture because food may become tender, firm, crisp, smooth or thickened depending on the method used.
• Preparation and cooking can improve overall palatability by making food look, smell, taste and feel more appealing to eat.
• Heat can be transferred to food by conduction, convection and radiation.
• Conduction transfers heat to food through direct contact with a hotter surface or substance.
• In conduction, heat passes from particle to particle through a material from the hotter region to the cooler region.
• Metal saucepans, frying pans and baking tins are often used in cooking because metal is a good conductor of heat energy.
• A metal pan conducts heat from the hob to the part of the food that touches the pan.
• Convection transfers heat energy through a liquid or gas.
• In convection, heated liquid or gas particles rise and cooler particles move in to replace them.
• The continuous movement of warmer and cooler particles forms a convection current.
• Water in a pan and hot air in a convection oven transfer heat to food by convection currents.
• Radiation transfers heat to food by electromagnetic waves, mainly infrared energy from a grill or heating element.
• Grills and toasters cook food mainly by radiation because heat travels directly from the element to the food surface.
• Microwave ovens heat food by microwave radiation, which excites water molecules within the food.
• A sauce is heated by conduction where it touches the pan and by convection as the liquid circulates.
• Agitating a sauce by stirring or whisking helps distribute heat evenly and reduces the risk of sticking, lumps and burning.
• Grilling uses radiation to brown, char or toast the surface of foods such as vegetables, meat, fish, halloumi, seeds and nuts.
• Selecting a cooking method requires matching the method, temperature and cooking time to the food so the final dish has the intended appearance, flavour, texture and nutritive value.
• Cooking methods are grouped into water-based methods, dry heat methods and fat-based methods.
• The structure of a food affects the best cooking method because delicate proteins, starchy foods and tough connective tissue respond differently to heat.
• Water-based methods help prevent food from drying out, but water-soluble vitamins such as vitamin C and B vitamins can leach into the cooking liquid.
• Dry heat methods are chosen when browning, caramelisation or a crisp surface is required.
• Fat-based methods transfer heat quickly and promote browning, but they usually increase the energy and fat content of the finished dish.
• Using short cooking times, small pieces and as little water as possible usually helps conserve nutrients.
• Cooking liquid that is served as part of the dish can retain water-soluble nutrients that moved out of the food during cooking.
• Water-based cooking methods include steaming, boiling, simmering, blanching, poaching and braising.
• Steaming cooks food by surrounding it with steam above boiling liquid.
• Steaming is suitable for vegetables, fish and other delicate foods because it cooks gently without immersing food in water.
• Steaming usually conserves more water-soluble vitamins than boiling because the food does not sit in the cooking liquid.
• Steaming can preserve colour and texture when food is cooked for the correct time, but over-steaming makes food soft and dull.
• Boiling cooks food in liquid at about 100 degrees Celsius.
• Boiling is suitable for foods that need full softening, such as pasta, rice, potatoes and some vegetables.
• Boiling can cause flavour, colour and water-soluble nutrients to move into the liquid, so it is less suitable for delicate foods when the liquid is discarded.
• Vigorous boiling can break up delicate foods and overcook vegetables.
• Simmering cooks food in liquid just below boiling point.
• Simmering is suitable for soups, sauces, curries and stews because gentle heat cooks food evenly and allows flavours to develop.
• Simmering is more suitable than vigorous boiling for delicate foods because the liquid moves less aggressively.
• Long simmering can soften connective tissue in tougher cuts of meat, but long cooking reduces colour and nutrient content in vegetables.
• Blanching cooks food briefly in boiling water and then cools it quickly to stop further cooking.
• Blanching is used to loosen skins, reduce enzyme activity before freezing and partly cook foods before a second cooking method.
• Blanching helps preserve colour and texture when the food is cooled quickly after heating.
• Poaching cooks food gently in liquid kept below boiling point.
• Poaching is suitable for eggs, fish, fruit and other delicate foods that would break up in boiling liquid.
• Poaching uses no added fat and produces a tender texture, but it does not create browning or roasted flavour.
• Braising cooks food slowly in a small amount of liquid in a covered pan or casserole, often after initial browning.
• Braising is suitable for tougher cuts of meat and firm vegetables because slow moist heat softens connective tissue and develops flavour.
• Braising can conserve nutrients better than boiling when the cooking liquid is served with the dish, but long cooking can soften vegetables excessively.
• Dry heat cooking methods include baking, roasting, grilling and dry frying.
• Baking cooks food by dry heat in an oven.
• Baking is suitable for breads, cakes, pastry dishes and some savoury dishes that need steady, even heat.
• Baking can create a firm structure and browned surface, but too much heat or time can dry food out.
• Roasting cooks food by dry heat in an oven, often with some added oil or fat on the surface.
• Roasting is suitable for meat, poultry, potatoes and root vegetables because dry heat can brown the outside while cooking the centre.
• Roasting promotes Maillard browning and caramelisation, which create a darker colour and richer flavour.
• Roasting can reduce heat-sensitive vitamins and can dry food out if the temperature is too high or the cooking time is too long.
• Grilling cooks food with intense radiant heat from above or below.
• Grilling is suitable for thin or tender foods such as fish fillets, kebabs, burgers and sliced vegetables because it cooks the surface quickly.
• Grilling browns the surface and can allow fat to drain away from meat, but food can burn easily if it is too close to the heat source.
• Dry frying cooks food in a pan without added fat.
• Dry frying is suitable only for foods that release enough natural fat, such as bacon or minced meat.
• Dry frying can create browning and crisp texture, but food is likely to stick or burn if it does not release enough fat.
• Fat-based cooking methods include shallow frying and stir-frying.
• Shallow frying cooks food in a small amount of hot fat or oil in a pan.
• Shallow frying is suitable for foods such as eggs, pancakes, fish fillets and burgers because hot fat cooks the surface quickly.
• Shallow frying creates a browned, crisp exterior and strong flavour, but it increases the fat and energy content of the dish.
• Preheating oil for shallow frying helps the surface cook quickly and reduces how much oil the food absorbs.
• Overcrowding a pan during shallow frying lowers the oil temperature and makes food absorb more fat.
• Stir-frying cooks small, similar-sized pieces of food quickly over high heat in a small amount of oil, usually in a wok.
• Stir-frying is suitable for vegetables, noodles, tofu and strips of meat because fast cooking helps food stay crisp and colourful.
• Stir-frying can conserve nutrients relatively well because cooking times are short, but the food must be kept moving to prevent burning.
• Selecting the correct cooking method changes appearance, colour, flavour, smell and texture, which together determine palatability.
• Browning reactions such as Maillard browning and caramelisation create new flavours, aromas and colours when foods are cooked with dry heat.
• Overcooking usually dulls the colour of vegetables, softens texture excessively and weakens flavour.
• Seasoning with herbs, spices, salt, pepper, citrus or sauces can improve palatability by adding or balancing flavour.
• Glazing adds shine and can improve appearance and flavour by coating food with a reduced sauce, syrup or egg wash.
• Garnishing improves the visual appeal of a dish and can add contrast in colour, flavour or texture when the garnish is edible and relevant.
• Marinades add flavour and can tenderise meat or meat alternatives because acidic ingredients and enzymes can begin to denature proteins.
• Cutting ingredients into even-sized pieces helps them cook at the same rate and improves final texture and appearance.
• An oven should be preheated so that food starts cooking at the correct temperature and the recipe achieves the intended rise, texture and cooking time.
• The oven is used for baking, roasting, braising, casseroles and tagines.
• Casseroles and tagines cook food slowly in a covered vessel with liquid, which helps flavours blend and tougher ingredients tenderise.
• A tagine is both a North African cooking pot with a conical lid and the slow-cooked dish prepared in it.
• A grill allows the cook to control browning by adjusting shelf height and distance from the heat source.
• Microwave cooking heats food by exciting water molecules in the food.
• Microwave cooking is quick and can conserve nutrients well because it usually uses short cooking times and little water.
• Microwave cooking does not brown food effectively, so it is less suitable when a crisp texture or roasted flavour is required.
• Protein denaturation is the unfolding of a protein's amino acid chain.
• Proteins in food can be denatured by acid, mechanical action or heat.
• Acidic ingredients such as lemon juice or vinegar can denature proteins in foods such as meat and fish.
• Mechanical action such as whisking egg whites or kneading dough can denature proteins.
• Heating proteins during cooking can denature them and change the texture and appearance of food.
• Protein denaturation underlies important functional changes in food, including coagulation, gluten formation and foam formation.
• Protein coagulation happens when denatured proteins bond together into a network that traps water.
• Protein coagulation changes the texture and appearance of protein-rich foods.
• Overcooking can squeeze water out of coagulated proteins, making food dry, firm and dense.
• Heating an egg mixture causes egg proteins to denature and coagulate, which sets dishes such as quiche.
• Heating meat causes meat proteins to coagulate and shrink.
• Milk proteins can denature when heated or when acid is added.
• Curdling happens when denatured milk proteins clump together so that milk separates into curds and whey.
• Cheese is made by removing the whey from curds and processing the curds.
• Gluten forms when water is added to wheat flour and allows the proteins glutenin and gliadin to join together.
• Kneading develops gluten into a strong elastic network throughout dough.
• A developed gluten network allows dough to stretch, expand and hold trapped gas.
• During baking, gluten coagulates and helps dough keep its risen structure.
• Foam formation happens when air is introduced into a protein-containing liquid by whisking or beating.
• Whisking denatures protein molecules and stretches them into strands around air bubbles.
• The denatured proteins form a mesh that traps air and stabilises the foam.
• Heating a protein foam sets the protein network into a solid structure.
• Egg whites whisked to soft peaks are only partly denatured, so the foam can lose air and collapse over time.
• Egg whites whisked to hard peaks are more fully denatured and form a more stable foam.
• Over-whisking can break the protein network and cause a foam to collapse.
• Functional properties describe what proteins do in food, such as setting a mixture or forming a foam.
• Chemical properties describe how changes in protein structure, such as denaturation and coagulation, make those functions possible.
• Tenderising makes meat softer by breaking down structures in the muscle.
• Acidic marinades can tenderise meat and some protein alternatives by denaturing proteins near the surface.
• Mechanical tenderising methods such as pounding or mincing physically break down muscle fibres.
• Long, slow cooking can tenderise some cuts of meat by gradually softening their structure.
• Marinating means soaking foods such as meat, fish, tofu or vegetables in a flavoured liquid for a period of time.
• A marinade can add flavour and moisture as well as contributing to tenderising.
• Marinades often contain herbs, spices and acids such as lemon juice or vinegar.
• Gluten formation is most important in bread and pasta doughs because they need structure and elasticity.
• Adding water starts gluten formation, and kneading develops the gluten network further.
• In bread dough, a strong gluten network allows the dough to expand without collapsing as gas is produced.
• Bread dough is proved so that yeast ferments and releases carbon dioxide, which the gluten network traps.
• During baking, yeast is killed and the expanding gas helps produce a light texture while coagulated gluten fixes the final shape.
• A bread machine develops dough by mixing, kneading and proving it before baking.
• A pasta machine rolls gluten-developed dough to a consistent thickness for shaping.
• Protein coagulation can set liquid mixtures during cooking.
• Heating an egg-based mixture causes the proteins to denature and coagulate, turning the mixture from liquid to solid.
• Quiche filling sets during baking because egg proteins coagulate.
• Egg-based mixtures set by protein coagulation rather than by gelation.
• Carbohydrates in food include starch and sugars.
• Cooking can change carbohydrates in ways that alter a food's colour, flavour and texture.
• Gelatinisation is the thickening of a liquid when starch is heated with water or another liquid.
• Heat and liquid are both needed for starch gelatinisation to happen.
• During gelatinisation, starch granules absorb liquid, swell and eventually burst, releasing starch into the surrounding liquid.
• Gelatinisation explains why starch-based mixtures such as sauces, gravies and some custards thicken during cooking.
• Gelatinisation also happens when starchy foods such as rice, pasta and potatoes are cooked in liquid.
• A higher starch-to-liquid ratio produces a thicker mixture during gelatinisation.
• A starch-thickened mixture may set into a gel as it cools.
• Dextrinisation happens when dry heat breaks starch down into smaller molecules called dextrins.
• Dextrinisation mainly happens in starchy foods cooked by dry methods such as baking and toasting.
• Dextrinisation causes browning and can produce a crisper texture and sweeter flavour.
• Longer heating increases the extent of dextrinisation.
• Caramelisation happens when sugars are heated to a high temperature and begin to break down.
• During caramelisation, sugars break down and release water.
• Caramelisation gives foods a brown colour and a characteristic sweet caramel flavour.
• Vegetables can caramelise when high-temperature cooking breaks down their natural sugars.
• Burnt sugar gives food a bitter taste, so controlling heat is important during caramelisation.
• Browning in meat and fish is not caramelisation because it mainly involves proteins rather than sugars.
• Starch-based sauces thicken because starch gelatinises as the sauce is heated.
• In a starch-based sauce, flour or cornflour granules swell and burst at about 80 °C, helping the sauce thicken.
• Using more starch makes a sauce thicker, and using more liquid makes a sauce thinner.
• In the roux method, flour is cooked with fat to make a paste before liquid is added gradually.
• Adding liquid gradually to a roux helps prevent lumps forming in the sauce.
• In the all-in-one method, fat, flour and liquid are combined from the start and heated while the mixture is stirred or whisked.
• In the blended method, starch is mixed with cold liquid to form a smooth paste before hot liquid is added and the sauce is heated.
• An infused sauce is made by steeping flavourings such as bay or peppercorns in the liquid before the sauce is thickened.
• A veloute is a roux-based sauce made with stock instead of milk.
• A bechamel is a roux-based white sauce made with milk and is often prepared as an infused sauce.
• In sauce making, conduction transfers heat from the hob to the pan and from the pan to the sauce touching the pan.
• In sauce making, convection currents transfer heat through the liquid as warmer sauce rises and cooler sauce sinks.
• Stirring or whisking a starch-based sauce distributes heat, reduces sticking and helps prevent lumps during gelatinisation.
• Fats and oils have key functional properties in food preparation, including shortening, aeration, plasticity and emulsification.
• Shortening is the functional property of fats that gives pastry and biscuits a short, crumbly texture.
• Rubbing fat into flour coats the flour particles with fat before water is added.
• The fat coating limits contact between flour proteins and water, so only a weak gluten network forms.
• Limited gluten development makes shortened dough crumbly rather than stretchy and elastic.
• Creaming fat with sugar traps many small air bubbles in the mixture.
• During baking, the trapped air expands and helps mixtures made by the creaming method develop a light, spongy texture.
• Fats and oils are mainly made of triglycerides containing saturated or unsaturated fatty acids.
• Fats rich in saturated fatty acids usually have higher melting points and are more likely to be solid at room temperature.
• Oils rich in unsaturated fatty acids usually have lower melting points and are more likely to be liquid at room temperature.
• Plasticity is the ability of a fat to soften over a range of temperatures instead of melting at one exact temperature.
• Plasticity happens because different triglycerides in the same fat have different melting points.
• A plastic fat can be spread or creamed at room temperature without becoming fully liquid.
• Fat and water are immiscible, so they do not mix evenly without help.
• An emulsion is a mixture in which tiny droplets of one liquid are dispersed through another liquid.
• Oil-in-water emulsions such as mayonnaise and salad dressing contain oil droplets dispersed through a water phase.
• Water-in-oil emulsions such as butter and margarine contain water droplets dispersed through a fat phase.
• An emulsifier stabilises an emulsion by helping fat and water stay mixed instead of separating.
• Emulsifier molecules have a hydrophilic region that interacts with water and a hydrophobic region that interacts with fat.
• Lecithin in egg yolk acts as an emulsifier in mayonnaise and hollandaise sauce.
• Enzymic browning is a reaction that turns the cut surfaces of some fruit and vegetables brown after they are exposed to air.
• Enzymic browning happens when damaged plant cells allow enzymes and oxygen to react together.
• Enzymes are proteins that act as biological catalysts, so they speed up chemical reactions without being used up.
• Enzymic browning reduces the quality of fruit and vegetables by making them look less appealing and sometimes affecting flavour.
• Apples, pears, bananas and potatoes are common examples of foods that can brown enzymically after cutting or peeling.
• Lemon juice slows enzymic browning because its acidity lowers pH and reduces the activity of the enzymes responsible for browning.
• Preventing cut fruit or vegetables from contacting oxygen slows enzymic browning.
• Blanching fruit or vegetables briefly in boiling water denatures enzymes and helps prevent enzymic browning.
• Blanching is often used before freezing because freezing slows enzyme activity but does not destroy enzymes completely.
• Oxidation is a chemical reaction in which oxygen reacts with substances in food and can reduce nutritional value.
• Vitamin C is especially vulnerable to oxidation in fruit and vegetables.
• B vitamins and vitamin C are water-soluble vitamins.
• Cutting fruit or vegetables and leaving them exposed to air for longer increases vitamin loss by oxidation.
• Preparing fruit or vegetables as close as possible to serving or cooking time helps reduce vitamin loss by oxidation.
• Adding vegetables to water only when it is already boiling helps reduce cooking time and can limit vitamin loss.
• Cooking vegetables for the shortest effective time helps reduce the loss of water-soluble vitamins.
• Overcooking vegetables increases the loss of water-soluble vitamins.
• Serving vegetables soon after cooking helps limit further vitamin loss.
• Raising agents make mixtures rise because gases expand during heating and create a lighter, more open texture.
• The four main types of raising agent used in food preparation are chemical raising agents, mechanical raising agents, steam and biological raising agents.
• Chemical raising agents raise mixtures by producing carbon dioxide gas.
• Bicarbonate of soda is an alkali that releases carbon dioxide when it reacts with an acid in the presence of moisture and heat.
• If bicarbonate of soda is not fully neutralised by an acid, the finished product can have an alkaline taste and a yellow-brown colour.
• Baking powder contains bicarbonate of soda and acid salts, so it can produce carbon dioxide when mixed with liquid and heated without needing an acidic ingredient in the recipe.
• Self-raising flour is plain flour with baking powder already added, so it is used when a recipe needs a moderate and even rise.
• Chemical raising agents must be measured accurately because too little gives poor volume, while too much can cause coarse texture, tunnelling or an unpleasant flavour.
• Mechanical raising agents work by incorporating air into a mixture before cooking.
• Whisking incorporates air into ingredients such as egg white or cream and can produce a foam that expands during heating.
• Egg white foam is a gas-in-liquid foam in which air bubbles are held in a network of partially denatured egg proteins.
• Beating incorporates air into mixtures such as batters by agitating ingredients rapidly.
• Folding combines a light aerated mixture with heavier ingredients while minimising the loss of trapped air.
• Sieving flour helps aeration by separating particles and introducing air.
• Creaming fat and sugar traps air bubbles that expand during baking and help cakes rise.
• Rubbing fat into flour introduces air and also helps produce a short texture by limiting gluten development.
• Steam is produced when water in a moist mixture reaches boiling point.
• Steam acts as a raising agent because water expands greatly when it changes from liquid water to steam.
• Steam raising is most effective in mixtures with a high water content and a structure that can set quickly, such as choux pastry and Yorkshire pudding batter.
• Yeast is a single-celled micro-organism used as a biological raising agent in bread making.
• During fermentation, yeast uses sugars and produces carbon dioxide and ethanol.
• The carbon dioxide from yeast becomes trapped in the gluten network of dough and makes the dough expand during proving.
• Proving is the stage in bread making when dough is left in warm conditions so yeast ferments and the dough increases in volume.
• Warmth, moisture, a food supply and time all affect yeast activity, but excessive heat kills yeast.
• Baking causes the gases in bread dough to expand further, sets the dough structure, kills the yeast and evaporates most of the ethanol.
• Whisked egg acts as a raising agent in products such as meringues, souffles and savoury roulades because the trapped air expands during heating.
• Self-raising flour and baking powder are commonly used in cakes, scones and similar baked products that do not need yeast fermentation.
• Choux pastry and batter mixtures rely mainly on steam for their rise, so they must contain enough water to generate steam in the oven.
• Bread dough depends on gluten development as well as yeast activity because the gluten network must be strong enough to retain carbon dioxide.
• Overmixing an aerated mixture after air has been incorporated can force gas out and reduce the final rise.

• Analyse how conduction, convection and radiation transfer heat in a named cooking process such as sauce making, oven cooking or grilling.
• Explain why a food is cooked in terms of safety, flavour, texture, shelf life or dietary variety in a given example.
• Select a preparation and cooking method that produces a specified change in appearance, colour, flavour, texture, smell or palatability.
• Compare water-based, dry-heat and fat-based cooking methods for their effects on nutritive value and sensory properties.
• Justify when steaming, boiling, simmering, blanching, poaching or braising is the most appropriate method for a given ingredient.
• Justify when baking, roasting, grilling, dry frying, shallow frying or stir-frying is the most appropriate method for a given ingredient.
• Adapt cooking time, temperature, piece size or water volume to reduce losses of water-soluble vitamins during preparation and cooking.
• Evaluate how seasoning, browning, glazing, garnishing or marinating could improve the palatability of a finished dish.
• Justify the use of an oven, grill, hob or microwave for a stated food outcome.
• Explain how agitation helps a starch-based sauce cook evenly and prevents lumps, sticking or burning.
• Calculate how changing the starch-to-liquid ratio will alter the viscosity of a sauce.
• Interpret evidence of gelatinisation, dextrinisation and caramelisation in cooked foods.
• Explain how acid, heat or mechanical action denatures proteins in foods such as eggs, meat, fish or milk.
• Analyse how coagulation sets egg mixtures and how overcooking changes their texture.
• Plan how to develop gluten in bread or pasta dough so the structure can stretch and retain gas.
• Evaluate the stability of an egg foam by distinguishing between soft peaks, hard peaks and over-whisking.
• Explain how rubbing in, creaming and the plasticity of fat affect the texture of pastry and cake mixtures.
• Select an appropriate emulsifier and method to stabilise an emulsion such as mayonnaise, hollandaise or salad dressing.
• Compare methods for preventing enzymic browning and oxidation in prepared fruit and vegetables.
• Justify the choice of chemical, mechanical, steam or biological raising agents for a named product.