Food Preparation Overview (Leaving Cert Home Economics): Revision Notes
Food Preparation Overview
Food preparation involves various processes that transform raw ingredients into meals. Understanding the science behind these changes helps you appreciate why certain techniques are used and what happens to food during preparation and cooking.
Changes that occur during food preparation
Before we even start cooking, several important transformations can happen to food during the initial preparation stages. These physical and chemical changes affect both the appearance and nutritional value of our ingredients.
Size increases in certain foods
When some foods come into contact with water, they expand significantly. This happens most commonly with foods that contain starch.
Size increase occurs when starchy foods absorb water and expand, particularly during soaking or initial cooking phases.
Worked Example: Starch Expansion
- Dried beans and lentils double or triple in size when soaked overnight
- Rice grains swell as they absorb cooking liquid
- Pasta expands when placed in boiling water
This expansion happens because starch molecules absorb water and swell, creating the larger volume we observe.
Making tough foods tender
Some foods, particularly meat, benefit from processes that break down their tough fibres before cooking begins.
Tenderising refers to techniques that break down tough muscle fibres and connective tissues to make food easier to chew and digest.
Common tenderising methods:
- Marinating meat in acidic solutions like vinegar or lemon juice
- Using enzyme-based marinades containing pineapple or papaya
- Mechanical tenderising through pounding or scoring
Acidic marinades work by denaturing proteins, while enzymes like those found in pineapple directly break down protein structures.
Loss of nutrients during preparation
Unfortunately, some valuable nutrients can be lost even before cooking begins, mainly through certain preparation techniques.
Nutrient loss happens when vitamins and minerals are removed or destroyed during food preparation, often through peeling, cutting, or excessive washing.
Examples of nutrient loss:
- Peeling potatoes removes vitamin C and B vitamins found just under the skin
- Cutting vegetables long before use leads to vitamin C degradation
- Soaking vegetables for extended periods leaches water-soluble vitamins
Colour changes in fresh foods
Some foods naturally change colour when exposed to air during preparation, which can affect their appearance and nutritional value.
Colour change during preparation typically results from oxidation reactions when cut surfaces are exposed to air.
Common Examples of Oxidation:
- Apples and pears turning brown after being cut
- Avocados developing brown spots when exposed to air
- Bananas darkening due to enzymatic browning
This browning occurs when enzymes in the fruit react with oxygen in the air, creating brown compounds called melanoidins.
Why we cook food
Cooking serves several essential purposes beyond simply making food hot. Understanding these reasons helps explain why cooking techniques have developed across cultures.
Enhancing taste and aroma
Heat releases and develops flavours that make food more appealing to our senses. Raw ingredients often have quite different taste profiles compared to their cooked versions.
Making food easier to digest
The cooking process breaks down complex food structures, making it much easier for our digestive systems to extract nutrients efficiently.
Ensuring food is safe to eat
Heat destroys harmful microorganisms that could cause food poisoning, making cooking a crucial food safety measure.
Improving food texture
Cooking can transform textures, making foods more pleasant to eat and easier to chew, particularly important for tough ingredients.
These four main purposes of cooking work together - a well-cooked meal will be flavorful, digestible, safe, and have an appealing texture.
Changes that occur during cooking
The cooking process triggers various physical and chemical transformations that alter food's appearance, texture, and nutritional content.
Foods becoming smaller during cooking
Many foods reduce in size when heated, primarily due to moisture and fat loss.
Shrinkage occurs when food loses volume or mass during cooking, usually because water evaporates or fats melt away.
Examples of Food Shrinkage:
- Meat shrinking on the grill as juices evaporate and fat renders out
- Vegetables reducing in size as their water content decreases
- Mince becoming more compact as cooking progresses
Understanding shrinkage helps explain why recipes often call for larger amounts of raw ingredients than the final serving size.
Softening of food textures
Heat breaks down the internal structure of foods, generally making them softer and easier to eat.
Examples:
- Hard vegetables like carrots becoming tender when boiled
- Tough cuts of meat becoming tender through slow cooking methods
- Rice grains softening as they absorb liquid and heat
Nutrient changes during cooking
While cooking can destroy some nutrients, it can also make others more available to our bodies.
Nutrient loss during cooking involves the destruction or leaching of vitamins and minerals, though some nutrients may become more bioavailable.
Common nutrient changes:
- Water-soluble vitamins like vitamin C dissolving into cooking water
- Heat-sensitive vitamins breaking down at high temperatures
- Some nutrients becoming more bioavailable through cooking
While some vitamin C is lost during cooking, cooking tomatoes actually increases the availability of lycopene, a beneficial antioxidant.
Colour transformations through heat
Cooking often produces distinctive colour changes through various chemical reactions.
Colour change during cooking results from chemical reactions, particularly the Maillard reaction which creates browning and develops flavours.
Worked Example: Maillard Reaction in Action
- Bread crust turning golden brown during baking
- Meat developing an appetising brown exterior when seared
- Onions becoming translucent and golden when sautéed
The Maillard reaction occurs between amino acids and sugars at temperatures above 140°C (285°F), creating hundreds of different flavour compounds and the characteristic brown colour.
Texture modifications through heat
Heat fundamentally alters the physical structure of ingredients, usually making them softer and more palatable.
Examples:
- Raw flour becoming light and airy in baked goods
- Hard grains like rice becoming fluffy and tender
- Firm vegetables becoming soft and easy to chew
Thickening of liquids
Heat can concentrate liquids and activate thickening agents, changing the consistency of sauces and soups.
Thickening involves making liquids denser, either through evaporation of water or by adding thickening agents that activate with heat.
Methods of thickening:
- Reducing sauces through evaporation
- Adding flour or cornflour to create thicker consistencies
- Using egg yolks or cream to enrich and thicken mixtures
Key Points to Remember:
- Physical changes during preparation include size increases, tenderising, and colour changes, while chemical changes involve nutrient loss and oxidation reactions
- Cooking food serves four main purposes: enhancing flavour, improving digestibility, ensuring safety, and modifying texture
- During cooking, foods undergo shrinkage, softening, nutrient changes, colour transformations through reactions like Maillard browning, and thickening of liquids
- Understanding these changes helps you choose appropriate cooking methods and preparation techniques for different ingredients
- Both preparation and cooking can cause nutrient loss, but cooking also makes many foods safer and more digestible