Discuss the principle of pressure cooking and canning in detail. Identify four pieces of equipment for food preparation and their uses. Discuss heat transfer in food preparation using at least four media of heat transfer. Describe how to measure brown sugar, flour, and oil. Explain the two types of boiling and steaming. Explain how utensils and food handlers can be sources of infection during food preparation.

1. Principle of pressure cooking (5 marks)

Pressure cooking operates on the principle that increasing the pressure inside a sealed container raises the boiling point of water, allowing food to cook at higher temperatures than the standard $100^\circ$C at atmospheric pressure.

Step 1: Normal boiling occurs at $100^\circ$C under $1$ atm pressure, but heat cannot exceed this without vaporizing all water.

Step 2: In a pressure cooker, the tight-fitting lid traps steam, building pressure (typically $15$ psi above atmospheric, or about $2$ atm total).

Step 3: This raises the boiling point to approximately $121^\circ$C, enabling faster heat transfer and cooking times reduced by up to $70\%$ (e.g., tough meats soften quicker due to higher temperature accelerating protein denaturation and collagen breakdown).

Step 4: A safety valve releases excess pressure to prevent explosion, and a gasket ensures seal integrity.

Advantages include nutrient retention (shorter cooking preserves vitamins), energy efficiency, and suitability for high-altitude areas where boiling point is lower.

2. Four pieces of equipment for food preparation with their media of heat transfer to food (8 marks)

Identify four equipment and link each to a heat transfer medium (conduction, convection, radiation):

• Saucepan on stovetop: Conduction – Heat transfers directly from hot pan surface to food via molecular contact.

• Oven: Convection – Hot air circulates, carrying heat to food; radiation from oven walls also contributes.

• Steamer: Convection via steam – Water vapor transfers latent heat evenly to food without submersion.

• Grill: Radiation – Infrared waves from heating element directly heat food surface; conduction from grates.

Each medium ensures efficient preparation: conduction for searing, convection for even baking, etc.

3. Measuring ingredients (9 marks)

i. Brown sugar: Pack firmly into a dry measuring cup using a spoon or fingers until level with the rim, then level off with a straight edge (knife/spatula). Do not scoop directly from bag to avoid air pockets. This gives accurate weight due to its moisture content.

ii. Flour: First, fluff the flour in its container with a fork to aerate. Spoon lightly into a dry measuring cup until overflowing, then level off with a straight edge without tapping or shaking (prevents compaction). For precision, sift if lumpy. Avoid scooping directly as it packs denser, yielding up to $25\%$ more.

4 & 5. Two types of boiling and steaming with examples (6 marks)

The two moist heat methods are boiling and steaming.

Boiling: Food fully submerged in water at $100^\circ$C.

• Rapid (rolling) boil: Vigorous bubbles; example – pasta (breaks starches quickly but risks nutrient loss).
• Gentle simmer: Smaller bubbles ($85$-$95^\circ$C); example – soups/stews (tenderizes without breaking texture).

Steaming: Food above boiling water, cooked by rising vapor (retains more nutrients).
Examples: Vegetables in bamboo steamer (crisp texture); dumplings (prevents sogginess).

6. Sources of infection in food preparation (9 marks)

i. Utensils: Can harbor pathogens (e.g., Salmonella, E. coli) if not sanitized after use with raw meat. Cross-contamination occurs via residue; solution – wash in hot soapy water ($60^\circ$C+), sanitize with bleach solution ($50$ ppm).

ii. Food handler: Transmits infection via poor hygiene (unwashed hands after toilet), illness (e.g., norovirus vomiting), or uncovered wounds. Example – handler with staph infection contaminates salad; prevent with handwashing ($20$ seconds soap), gloves, hairnets, health checks.