Food Tech: Food Science

Why do we cook food?

• Kills harmful bacteria

• Improves flavour / texture / colour

• Adds variety to the diet

• Improves the keeping quality

• Makes it easier to digest

What microorganisms are harmful in foods?

Yeast

Mould

Bacteria

What are the methods of transferring heat?

• Conduction - Pan to steak / water (Boiling / Frying)

• Convection - warm molecules rise, cooler molecules fall → close to the heat Boiling / Steaming

• Radiation - Microwave / grill

What factors influence the type of cooking methods used?

• Type of food

• Time

• Skill

• Consumer choice

• Individual needs (diet restrictions)

Types of cooking methods (Water-Based)

Blanching - Cooked, quickly cooled to stop cooking. Stops enzymic action in frozen veg.

Boiling (100º)	Quick, won’t burn	Lose water-sol vits, veg disintegrates
Simmering (85-90º)		Lose water-sol vits
Poaching (85º)		Lose water-sol vits
Steaming	Retains nutrients	Can take a long time

What are the dry cooking methods?

• Baking

• Roasting (added fat)

• Braising - Meat browned in pan, cooked in liquid and covered with lid

• Casserole - Small amount of liquid that simmers, covered with lid.

What are the dry, fat-based cooking methods?

• Frying - Deep/shallow/stir

• Dry-frying - No added fat, use naturally occurring fats to cook (sausages + bacon)

Golden brown, appealing

More difficult to digest, Excess fat unhealthy.

What are radiation cooking methods?

Grilling	Quick, Can trim fat before cooking	Can’t do tough meats
Microwave	Very quick, saves energy, convenient	Easy to overcook, pale colour

Which fats are visible, and which are invisible?

Visible - Butter, lard, oils

Invisible - Cheese

How is nutrition in foods affected by cooking?

Carbs	NSP is softened, starch reduced in water
Fat	Reduced (can drain out) / increased with fat based methods
Vit B’s	Water soluble, destroyed by heat (except B9, unless reheated)
Vit C	Destroyed by heat, water soluble

Why would shin beef be tough if grilled?

Lots of connective tissue and long fibres

Needs long, slow cooking to tenderise

What are the different food browning processes?

• Sugar - caramelisation

• Proteins / carbs - Maillard Reaction

• Carbs - Dextrinisation

• Fruits and veg - Enzymic Browning

How / Why are sugars used in foods?

• Aeration - sugar & fat traps air for light texture

• Preserving - High concentration prevents growth of microorganisms (Jams)

• Adds flavour and colour

How / Why are fats used in cooking?

Plasticity - When a fat can spread even when in fridge (soft margarine)

Shortening - Rubbed into flour, coats particles, prevents gluten formation, crumbly textures

Aeration - Fat and sugar traps air

Emulsions - Oil & liquid, salad dressings

Flavour and moisture

Preservation - Moisture extendsd shelf life

What is coagulation?

Moist or dry heat applied to proteins, it coagulates

Egg transparent → white

Muscles fibres coagulate (red → brown)

What is aeration in eggs?

Egg white contains protein albumin

The albumin is stretched and traps air

Once over whisked, they can’t return to aerated form as the protein has denatured.

What is gluten formation?

Gluten is the protein in flour

Gluten is developed during kneading.

High gluten flour is used in breads.

How are acids used in foods?

• Vinegar (acetic acid) Softens meat tissues, denatures proteins

• Lemon juice (Acetic acid) - Prevents oxidisation and enzymic browning. Helps protein mixtures form a gel.

What are the three types of raising agents?

Chemical - Bicarb / Baking powder. Produces CO2

Biological - Yeast. Produces CO2 via fermentation

Mechanical - Aeration, whisking / Steam during baking.

how is air added to foods?

• Folding and rolling (flaky pastry)

• Beating mixtures (batters)

• Creaming fat and sugars (Cakes)

• Sieving (Flour)

• Rubbing in fat (Shortcrust pastry)

• Whisking

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