Ingredients: Function, Quality and Storage
Commodity groups
Questions test the function of ingredients. Proteins (meat, fish, eggs, dairy, pulses) coagulate with heat and give structure. Carbohydrates (flour, rice, potato, sugar) provide bulk, sweetness and thickening; starch gelatinises in liquid. Fats (butter, oil, lard) carry flavour, conduct heat, shorten gluten and emulsify. Vitamins and minerals are micronutrients lost through heat, light, oxygen and leaching into water. Water is a solvent and a medium for heat transfer.
Raising agents
Yeast is biological and produces carbon dioxide by fermentation. Baking powder is chemical (an alkali plus acid plus starch) and works in two stages if double-acting. Bicarbonate of soda needs an acid to react. Steam and air are physical raising agents - choux pastry rises on steam, whisked egg white on trapped air.
Quality and seasonality
Assess freshness: bright eyes and red gills in fish, firm flesh that springs back, no off-odour; meat should be firm with a clean smell; vegetables crisp and unbruised. Seasonal buying improves quality and lowers cost. Traceability records matter for meat and shellfish.
Storage
Dry stores: cool, dry, dark, off the floor, labelled and rotated FIFO (first in, first out). Cold store: 0–5 °C, raw below cooked. Freezer: below −18 °C, wrapped to prevent freezer burn. Eggs stored away from strong-smelling foods; potatoes in the dark to prevent greening.
Worked example
A sponge cake fails to rise. Check the baking powder date - old baking powder loses potency - and confirm the batter was not over-mixed, which develops gluten and knocks out air. The raising agent is chemical; over-mixing is a technique fault, not an ingredient fault.
Traps
Confusing yeast (biological) with baking powder (chemical); forgetting that salt strengthens gluten and sugar weakens it; ignoring FIFO in store questions.