JC Home Economics cheat sheet

Energy values: carbohydrate 4 kcal/g (17 kJ/g), protein 4 kcal/g (17 kJ/g), fat 9 kcal/g (37 kJ/g), alcohol 7 kcal/g (29 kJ/g); water, minerals and vitamins supply 0 kcal/g.

Daily energy need = BMR × physical activity level (PAL); PAL is roughly 1.4–1.69 for a sedentary to moderately active adult and 1.7–2.0 for very active people.

Fat-soluble vitamins A, D, E and K need dietary fat for absorption and are stored in the liver and adipose tissue; water-soluble B-complex and C are not stored and excess is excreted in urine.

Deficiency pairs: vitamin C → scurvy; thiamine (B1) → beriberi; niacin (B3) → pellagra; vitamin D/calcium → rickets and osteomalacia; iron → anaemia; iodine → goitre; vitamin A → night blindness.

Protein: 20 amino acids, 9 indispensable for adults; high-biological-value foods (eggs, milk, meat, fish, soya) supply all nine; cereal proteins are limited in lysine, legume proteins in methionine.

Fibre target for adults is about 25–30 g/day; soluble fibre (pectin, oat and barley beta-glucan) binds bile acids and lowers LDL cholesterol, insoluble fibre (cellulose, lignin) adds bulk and shortens transit time.

Glycaemic index scale 0–100: low 55 or below (lentils, whole oats), medium 56–69, high 70 and above (white bread, glucose); fine milling and long cooking raise GI, while fat, fibre and acid lower it.

Iron absorption: haem iron (meat, liver) is absorbed at about 15–25%, non-haem iron (plants, eggs) at about 2–8%; vitamin C boosts non-haem uptake, while tannins in tea and phytates inhibit it.

Water: about 2.0–2.5 L of total fluid per day for adults, more in heat or heavy activity; water supplies no energy, and dark urine, thirst, headache and poor concentration signal dehydration.

Temperature control rules: fridge 0–5°C, freezer −18°C or colder, hot holding above 60°C, reheating to at least 74°C, and no more than 2 hours total in the 5–60°C danger zone.

Heat transfer modes: conduction by direct contact (pan base, griddle), convection by moving currents in air or liquid (fan oven, boiling water), radiation as infrared waves (grill, microwave).

Moist-heat temperatures: poaching 70–80°C, simmering 85–95°C, boiling 100°C at sea level, steaming about 100°C; dry-heat methods are baking, roasting, grilling, frying and microwaving.

Roux ratio is equal weights of fat and plain flour; cook white roux 2–3 minutes, blond 4–5 minutes, brown 8–10 minutes, then add liquid gradually while stirring. Béchamel = milk + white roux.

Starch gelatinisation occurs around 60–80°C as granules absorb water, swell and burst; on cooling the gel may set further (retrogradation), which is why sauces thicken when cold.

Browning reactions: Maillard browning between amino acids and reducing sugars starts around 140–165°C and needs dry heat; caramelisation involves sugar alone and begins around 160°C.

Setting temperatures: egg white 60–65°C, egg yolk 65–70°C, meat myosin 50–60°C; slow moist heat converts collagen to gelatine, while high heat toughens fibres and squeezes out water.

Four food-safety rules (clean, separate, cook, chill): wash hands for about 20 seconds, store raw meat below ready-to-eat food, cook poultry to 74°C, and refrigerate leftovers within 2 hours.

Emulsions: oil-and-water mixtures are temporary (vinaigrette), semi-permanent (mayonnaise stabilised by egg-yolk lecithin) or permanent (butter); oil must be added slowly while whisking to avoid splitting.

Budget identity: net income = fixed expenses + variable expenses + savings; a deficit occurs when expenses exceed income and a surplus when income exceeds expenses.

50/30/20 guideline: 50% of net income to needs, 30% to wants, 20% to savings and debt repayment; when income falls, wants are cut before needs.

Unit price = pack price ÷ pack quantity, converted to the same unit (for example per kilogram or per 100 g); a larger pack is not automatically cheaper per unit.

Ingredient lists are ordered by descending weight at manufacture, and nutrition panels are shown per 100 g and per serving, so check the stated serving size before comparing products.

Waste hierarchy: prevent > reduce > reuse > recycle > recover energy > dispose; composting food scraps and refilling containers rank above recycling.

Appliance efficiency: induction hob about 85–90%, electric solid plate about 55–70%, gas hob about 40%; a lid traps steam so the heat can be turned down, and matching pan diameter to ring cuts losses.

Food preservation principles: remove or bind water (drying, salting, sugaring), lower pH (pickling), lower temperature (chilling, freezing), exclude oxygen (canning, vacuum packing) or kill microbes (heat, irradiation).

Consumer rights cover safety, accurate information, choice, redress and consumer education; matching responsibilities are reading labels, keeping receipts, complaining promptly and using products as directed.

Sustainability measures: seasonal local produce cuts food miles, meal planning cuts waste, plant proteins and certified sustainable fish reduce environmental load, and separate collection enables recycling.