Welcome to the World of Food Science!
Hello! Welcome to one of the most exciting parts of your Food Preparation and Nutrition course. Have you ever wondered why bread turns brown in the toaster, why eggs go from clear to white when fried, or why sauces thicken up on the stove? That’s not just cooking—it’s science!
Don’t worry if science isn't usually your favorite subject. In this chapter, we are going to look at the "how" and "why" of cooking. Think of the kitchen as your laboratory and yourself as the scientist. Let’s dive in!
1. Why Do We Cook Food?
Before we look at the chemistry, we need to understand the basic reasons we bother to turn on the oven at all. There are two main reasons:
A. Making Food Safe to Eat
Raw foods, especially meat, poultry, and eggs, can contain harmful bacteria like Salmonella. Cooking food to a high enough temperature (usually 75°C) kills these bacteria so we don't get food poisoning.
B. Making Food Digestible and Palatable
Some foods, like flour or raw potatoes, are very hard for our bodies to digest when raw. Cooking softens them. It also makes food "palatable"—which is just a fancy word for tasty! Cooking improves the texture, flavour, appearance, and aroma (smell) of our meals.
Quick Review: We cook to stay safe and to make food taste and look great!
2. Heat Transfer: How Heat Moves
Heat doesn't just appear in food; it has to travel there. There are three main ways this happens:
Conduction
This is heat moving through direct contact. Imagine a pancake in a frying pan. The heat moves from the hob to the pan, and then directly into the pancake.
Analogy: Like a "Mexican Wave" in a stadium, the energy is passed from one person (molecule) to the next by touching.
Convection
This happens in liquids and gases (like water or air). When they are heated, the warm part rises and the cooler part sinks, creating a "circular current."
Example: Boiling pasta in a pot or baking a cake in an oven.
Radiation
This is heat moving in waves. There is no direct contact.
Example: A toaster or a grill. The glowing red heating element sends out heat waves that zap the surface of your food.
Memory Aid:
Conduction = Contact (Touching)
Convection = Currents (Moving air/water)
Radiation = Rays (Waves)
3. Working with Carbohydrates
Carbohydrates (starches and sugars) change a lot when we cook them. Here are the three big "-isations" you need to know:
Gelatinisation (Thickening)
When starch granules (like flour) are heated in a liquid, they swell up and eventually burst, releasing starch that thickens the liquid. This is how we make a Bechamel (white) sauce.
Step-by-step:
1. Starch granules are mixed with liquid.
2. At 60°C, they start to absorb water and swell.
3. At 80°C, they burst and the sauce gets thick.
4. At 100°C (boiling), the process is complete.
Dextrinisation (Browning Starch)
This happens when dry heat is applied to starchy foods. The starch molecules break down into smaller units called dextrins, which turn brown and taste sweeter.
Example: Toasting bread or the crust on a baked loaf.
Caramelisation (Browning Sugar)
This is when sugar is heated. It melts into a syrup and then turns brown and develops a rich flavour. Be careful—if you heat it too long, it turns black and bitter!
Example: Making caramel sauce or the brown top on a Crème Brûlée.
Key Takeaway: Starch thickens (gelatinisation) or browns with dry heat (dextrinisation). Sugar browns when heated alone (caramelisation).
4. Working with Proteins
Proteins are like tiny "coiled springs." When we cook them, they change shape.
Denaturation and Coagulation
Denaturation is when the protein coils "unfold" or change shape. This can happen because of heat, acid (like lemon juice), or physical agitation (whisking).
Coagulation is what happens next. The unfolded proteins join together in a solid clump.
Example: A raw egg is runny (denatured by heat), but as it cooks, it sets firm (coagulates).
Gluten Formation
Gluten is a protein found in wheat flour. When you add water and knead dough, two proteins (gliadin and glutenin) join to form gluten. It’s stretchy like a balloon, which helps bread rise!
Common Mistake: Don't confuse gluten with a carbohydrate; it is definitely a protein.
Foam Formation
When you whisk egg whites, you are trapping air bubbles. The protein denatures and stretches around the air, creating a foam.
Example: Meringues or whisked sponges.
Did you know? Adding acid (like lemon juice or vinegar) to milk can denature the protein and make it curdle. This is how some cheeses are started!
5. Working with Fats and Oils
Fats do more than just add calories; they have very specific jobs in the kitchen!
Shortening
When you rub fat into flour (like making shortcrust pastry), the fat coats the flour particles. This prevents long gluten strands from forming, resulting in a "short," crumbly texture that melts in your mouth.
Aeration
When you "cream" butter and sugar together for a cake, the sugar crystals trap tiny bubbles of air in the fat. This makes the cake light and fluffy.
Plasticity
This just means how easy a fat is to spread or shape. Some fats (like butter from the fridge) have low plasticity (hard), while others (like margarine) have high plasticity (soft and spreadable).
Emulsification
Usually, oil and water don't mix. An emulsifier (like lecithin in egg yolks) has one end that loves water and one end that loves oil. It holds them together!
Example: Mayonnaise is an emulsion of oil and vinegar held together by egg yolk.
6. Fruit, Vegetables, and Raising Agents
Enzymic Browning
Have you ever sliced an apple and seen it turn brown? That’s enzymic browning. When the fruit is cut, oxygen in the air reacts with enzymes inside the fruit (oxidation).
How to stop it: Add an acid (lemon juice) or blanch the veg in boiling water to "deactivate" the enzymes.
Raising Agents: Making Food Rise
We use these to get air/gas into mixtures so they aren't heavy and flat.
1. Chemical: Baking powder or Bicarbonate of Soda (releases CO2 gas).
2. Biological: Yeast (a living fungus that ferments sugar to produce CO2).
3. Physical: Whisking air into a mix or using steam (water turning to gas in a hot oven, like in Yorkshire puddings).
Key Takeaway: Raising agents create gas (CO2, air, or steam) which expands in the heat, making the food rise.
Final Quick Review Box
- Heat moves via: Conduction, Convection, Radiation.
- Starch: Thickens with liquid (Gelatinisation).
- Protein: Unfolds (Denaturation) and sets (Coagulation).
- Fat: Makes pastry crumbly (Shortening) and helps cakes rise (Aeration).
- Browning: Can be Dextrinisation (starch), Caramelisation (sugar), or Enzymic (fruit + air).
Don't worry if this seems like a lot of science! Just try to link each word to a real food you've cooked in class, and it will start to make perfect sense. Happy cooking!