Post-harvest Technology and Value Addition
Post-harvest Technology and Value Addition covers what happens to a crop after detachment: respiration, water loss, ripening, storage and processing - and how to keep losses small enough that the value added is real.
Core rules
- Respiration rate drives perishability; the Q₁₀ effect means cooling from 30 °C to 10 °C can cut respiration several-fold.
- Climacteric fruits (banana, mango, tomato) ripen with an ethylene burst and respond to ethylene; non-climacteric fruits (citrus, pineapple, grape) do not.
- Safe storage moisture: paddy about 14 %, maize 13 %, wet basis. Above this, mould and aflatoxin risk rise sharply.
- Wet basis MC % = (wet mass − dry mass) ÷ wet mass × 100; dry basis divides by dry mass instead.
- Curing (onion, potato, sweet potato) heals wounds and sets skins before storage; grading and packaging cut mechanical damage.
Worked example
1000 kg of paddy at 22 % MC is dried to 14 % MC. Dry matter is conserved: final mass = 1000 × (100 − 22) ÷ (100 − 14) = 907 kg. Water removed = 93 kg. A trader buying by weight at the higher moisture is partly buying water, which is why moisture discounts exist.
Traps that cost marks
Using dry-basis formulas on wet-basis figures; drying with humid ambient air and storing the grain anyway; mixing ethylene-producing fruit with ethylene-sensitive vegetables; cooling tropical produce below its chilling threshold; counting only weight loss and ignoring quality loss.