foodtech 2

Why is food cooked?

Food is cooked to make it safe to eat, improve shelf life, improve texture, develop flavour, improve sensory properties and give variety in the diet.

How does cooking make food safe?

Cooking at high enough temperatures kills harmful bacteria in foods such as meat, poultry and eggs. Some foods, like red kidney beans, must also be boiled to destroy natural toxins.

How can cooking improve shelf life?

High temperatures can destroy bacteria and mould, helping food last longer. Pasteurisation is an example because milk is heated to kill bacteria and then cooled.

How does cooking improve texture?

Cooking can soften foods, make foods easier to chew and digest, soften starch molecules, coagulate proteins, and create different textures such as crispy outside and soft inside.

How does cooking develop flavour?

Cooking causes chemical reactions such as caramelisation, browning and roasting, which create stronger flavours. Cooking can also allow flavours from different foods to combine.

What are sensory properties?

Sensory properties are the appearance, texture, taste, smell and aroma of food.

What are the three methods of heat transfer?

Conduction, convection and radiation.

What is conduction?

Conduction is heat transfer through a solid by particle vibration. Heat passes from hotter particles to cooler particles through direct contact.

Give an example of conduction in cooking.

A saucepan on a hob gets hot because heat transfers from the hob into the metal pan, then into the food.

Why are metals good conductors of heat?

Metals transfer heat quickly, so pans are often made from metal to cook food efficiently and evenly.

What is convection?

Convection is heat transfer through liquids or gases. Warm fluid rises, cooler fluid sinks, and this creates convection currents that transfer heat.

Give an example of convection in cooking.

Water boiling in a pan uses convection currents as hotter water rises and cooler water sinks.

What is radiation?

Radiation is heat transfer by waves. It does not need direct contact between the heat source and the food.

Give examples of radiation in cooking.

Grilling, toasting and microwaving use radiation to heat food.

What is boiling?

Boiling is cooking food in boiling liquid, usually water, at about 100°C.

What foods can be boiled?

Meat, potatoes, rice, pasta and vegetables.

What are advantages of boiling?

Boiling is simple, quick and does not require added fat.

What are disadvantages of boiling?

Water-soluble vitamins such as B and C can be lost into the cooking water. Over-boiling can make food look pale, soft and less flavoursome.

What is steaming?

Steaming cooks food using steam from boiling water or stock without direct contact with the water.

Why is steaming healthy?

No fat is added and fewer nutrients, colour, texture and flavour are lost compared with boiling.

What is blanching?

Blanching is part-cooking food briefly in boiling water, then placing it in cold water to stop cooking.

Why is blanching used?

It helps preserve colour, texture and vitamins, removes harsh flavours, loosens skins and prepares fruit and vegetables for freezing.

What is simmering?

Simmering is cooking food gently in liquid just below boiling point.

Why is simmering useful?

It is gentle, preserves more nutrients than boiling and is useful for soups, sauces and curries.

What is poaching?

Poaching is cooking food gently in liquid below boiling point, usually around 80°C.

What foods are poached?

Eggs, fish and fruit.

What is braising?

Braising is slow cooking food in a covered pot with a small amount of liquid, using both simmering and steaming.

Why is braising useful for tough meat?

Slow cooking helps tenderise tough meat and allows flavours from liquid, vegetables and herbs to be absorbed.

What is stir-frying?

Stir-frying cooks small pieces of food quickly in a small amount of hot oil, usually in a wok.

Why can stir-frying be healthy?

It uses little oil, cooks quickly and helps vegetables keep more nutrients.

What is shallow frying?

Shallow frying cooks food in a frying pan with a medium amount of fat or oil.

Why is shallow frying less healthy than stir-frying?

Food may absorb more fat because it sits in oil for longer.

What is baking?

Baking uses dry heat in an oven to cook foods such as bread, cakes, pastries, potatoes and fish.

What are advantages of baking?

Many foods can be baked, the outside browns and crisps, and the inside can stay soft.

What are disadvantages of baking?

It can take a long time, use lots of energy and dry food out.

What is grilling?

Grilling cooks food using high-temperature radiant heat from above or below.

Why can grilling be healthy?

No fat is added and fat can drip off food as it cooks.

What are disadvantages of grilling?

Food can burn, cook unevenly or become cross-contaminated if cooked meat is handled with utensils used for raw meat.

What is roasting?

Roasting cooks food using dry heat in an oven, usually at a higher temperature than baking, often with added fat.

What are advantages of roasting?

It creates a brown, crispy outside, keeps food moist and gives a rich flavour.

What are disadvantages of roasting?

It can add extra fat, take a long time and use lots of energy.

What is dry frying?

Dry frying cooks food in a pan without added fat or oil. Fat from the food may melt out during cooking.

Why is dry frying healthier?

No extra fat is added, so the food is usually lower in fat than shallow-fried food.

What is denaturation?

Denaturation is when protein molecules unravel and change shape due to heat, acid or mechanical action. This change is usually irreversible.

What causes protein denaturation?

Heat, acids such as lemon juice or marinades, and physical agitation such as whisking, beating or kneading.

What is coagulation?

Coagulation is when denatured protein molecules join together and set, changing from liquid/soft to firm/solid.

Give an example of coagulation.

Egg white changes from clear liquid to white solid when heated.

What happens if protein is overcooked?

Too much coagulation makes protein tighten, squeeze out water and become dry, tough or rubbery.

What is a foam?

A foam is formed when air is trapped inside a liquid containing protein, such as whisked egg white or whipped cream.

How are foams formed?

Whisking stretches protein molecules around air bubbles, trapping air and forming a foam.

Why can over-whisking damage a foam?

Over-whisking overstretches the protein, causing air to escape and the foam to collapse.

What is gluten?

Gluten is a protein found in wheat flour, and also in barley and rye. It gives dough elasticity and stretch.

How is gluten formed?

Gluten forms when water is mixed with flour. Kneading develops gluten strands, making dough stretchy and elastic.

Why is gluten important in bread?

Gluten traps gases during proving and baking, allowing bread to rise and form a light, airy texture.

What is gelatinisation?

Gelatinisation is when starch granules absorb liquid, swell and burst when heated, causing the liquid to thicken.

What temperature does gelatinisation happen at?

Gelatinisation usually occurs between about 62°C and 80°C.

What foods use gelatinisation?

Sauces, custards, gravies, lemon pie filling, rice, pasta and starchy foods.

What affects the thickness during gelatinisation?

The ratio of starch to liquid. More starch makes a thicker mixture.

What is dextrinisation?

Dextrinisation is when starch is exposed to dry heat and breaks down into dextrins, causing browning, crisping and flavour change.

Give examples of dextrinisation.

Toasted bread, baked biscuits and browned pastry.

What is caramelisation?

Caramelisation is when sugar is heated, turns brown and develops a caramel flavour.

What happens during caramelisation?

Sugar first melts, then becomes caramel-like, then hardens as it cools. If overheated, it burns and tastes bitter.

Give examples of caramelisation.

Crème brûlée topping, caramel sauce, roasted onions and browned vegetables.

What is aeration?

Aeration is incorporating air into a mixture to make it lighter and fluffier.

Give an example of aeration.

Creaming butter and sugar traps air, making cakes lighter.

What is shortening?

Shortening is when fat coats flour particles, preventing gluten formation and creating a short, crumbly texture.

Give examples of shortening.

Shortbread, pastry, biscuits and crumble toppings.

What is plasticity?

Plasticity is the ability of fats to spread, be shaped and softened over a range of temperatures.

Why is plasticity useful?

It allows fats to be spread, rubbed into flour, shaped and used in buttercream, pastry and cheese spreading.

What is emulsification?

Emulsification is when oil and water are held together in a stable mixture using an emulsifier.

Why do oil and water normally separate?

Oil and water do not naturally mix, so they separate unless an emulsifier holds them together.

What is an emulsifier?

An emulsifier has one end attracted to water and one end attracted to oil, helping oil and water stay mixed.

Give examples of emulsions.

Milk, mayonnaise, margarine, salad dressings and hollandaise sauce.

What emulsifier is found in egg yolk?

Lecithin.

What are raising agents?

Raising agents produce gases that expand when heated, making mixtures rise.

What gas makes food rise?

Carbon dioxide, steam or air can expand and make food rise.

What is bicarbonate of soda?

Bicarbonate of soda is a chemical raising agent that releases carbon dioxide when heated or mixed with acid.

What is baking powder?

Baking powder contains bicarbonate of soda and an acid, so it releases carbon dioxide during baking.

Why is yeast a biological raising agent?

Yeast is a living microorganism that ferments sugar to produce carbon dioxide and alcohol.

How does yeast make bread rise?

Yeast ferments sugar, producing carbon dioxide. The gas gets trapped in gluten, making dough rise.

What is fermentation?

Fermentation is when yeast breaks down sugar to produce carbon dioxide and alcohol.

How does steam act as a raising agent?

Water turns to steam during cooking. The steam expands and pushes the mixture up, making it rise.

How does air act as a raising agent?

Air is trapped by whisking, beating, sieving, rubbing in, folding or creaming. The air expands during baking and helps food rise.

What are microorganisms?

Microorganisms are tiny living things such as bacteria, moulds and yeasts. Some are harmless, but others cause food spoilage or food poisoning.

What conditions do microorganisms need to grow?

Warmth, moisture, food, suitable pH and time.

How can microorganism growth be slowed or stopped?

Change one or more growth conditions, such as chilling/freezing, drying, adding salt, adding acid or reducing time at room temperature.

What are high-risk foods?

High-risk foods are ready-to-eat foods that support bacterial growth if not stored correctly because they are moist, high in protein and around neutral pH.

Give examples of high-risk foods.

Cooked meat, fish, poultry, dairy products, eggs, gravies, sauces, cooked rice and shellfish.

Why is cooked rice high risk?

Cooked rice can contain bacteria that multiply if it is left warm for too long, so it must be cooled quickly and stored safely.

How can you identify spoiled meat?

Slimy surface, sour smell, mould or unusual appearance.

How can you identify fresh fish?

Fresh fish should have shiny skin, red gills, clear eyes and smell clean or slightly salty.

What are enzymes?

Enzymes are biological catalysts made from protein that speed up chemical reactions.

How do enzymes cause food spoilage?

Enzymes cause fruit to ripen, soften, change colour and break down starches into sugars.

What is enzymic browning?

Enzymic browning is when cut fruit reacts with oxygen and turns brown due to enzyme activity.

How can enzymic browning be prevented?

Add acid such as lemon juice, blanch the food, freeze it, or reduce exposure to oxygen.

How do moulds spoil food?

Moulds grow on food in warm, moist conditions and make it look, smell and taste unpleasant.

How do yeasts spoil food?

Yeasts ferment sugars in fruit, producing alcohol and carbon dioxide, which spoils food.

What is the danger zone?

The danger zone is 5°C to 63°C, where bacteria grow and multiply quickly.

What temperature should hot food be held above?

Hot food should be held above 63°C.

What temperature should cooked food reach?

Food should be cooked or reheated to at least 75°C to kill bacteria.