🍎 Harvesting, Handling and Grading

This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.

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Harvesting, Handling and Grading

Maturity Indices

Maturity indices are criteria used to determine the appropriate stage at which to harvest a commodity. Harvesting at the correct maturity stage is critical — too early gives poor quality and low yield; too late means faster deterioration during marketing.

Physical Maturity Indices

• Size: diameter (mango >65 mm for export), weight (strawberry >18 g for premium grade), length (banana finger girth 75–80% round)
• Colour: skin colour change from green to yellow/orange/red (tomato, capsicum, citrus); flesh colour (yellow flesh mango indicates maturity)
• Firmness: resistance to compression measured by penetrometer/pressure tester; apple at harvest: 16–18 lb force with 0.5-inch tip = harvest mature; dropping firmness signals senescence
• Specific gravity: denser potatoes (>1.08) indicate higher starch/dry matter content; apples denser than water = mature
• Ease of separation: natural abscission layer formation at pedicel — mango, avocado can be picked cleanly when mature; grapes form corky layer at berry attachment

Chemical Maturity Indices

• Soluble Solids Content (SSC / TSS): measured with hand refractometer (°Brix); primarily sucrose, glucose, fructose; increases with maturity; Alphonso mango ≥14–16°Brix for harvest
• Titrable Acidity (TA): measured by NaOH titration; decreases with ripening as organic acids are respired
• SSC:TA ratio (Maturity Ratio): most reliable single indicator for many fruits; citrus harvest when ratio >8:1; table grapes >20:1
• Starch content: decreases during maturation as starch converts to sugar; iodine staining test (apple): fresh cross-section stained with iodine; starch stains blue-black; less staining = more mature; starch index 1–8 scale
• Oil content: avocado maturity indicated by oil content >8%; critical for creaminess
• Anthocyanin development: colour charts for tomato, pepper

Physiological Indices

• Days from anthesis or full bloom: accumulated from full bloom to harvest; Red Delicious apple = 150–180 days; Alphonso mango = 110–120 days from flowering
• Accumulated Heat Units (Growing Degree Days, GDD): sum of mean daily temperature above base temperature; useful for sweet corn, peas
• Respiration rate / ethylene production threshold: threshold of 1 µL/kg/h ethylene signals climacteric onset in apples

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Maturity Standards for Major Crops

Maturity Standards Table

Crop	Physical Index	Chemical Index	Physiological Index
Mango (Alphonso)	Shoulder development; float in water for Langra, Dashehari	TSS ≥14–16°Brix; SA ratio >10	100–115 days from full bloom
Banana	Finger cross-section 75–80% round; pulp:peel ratio >1.5	—	100–120 days from shooting
Tomato	Jelly-like locular tissue visible; skin begins colour break	—	45–55 days from transplanting
Apple	Firmness 16–18 lb (0.5" tip); colour	SSC ≥11°Brix; starch index 5–6	150–180 days from full bloom
Wheat	Dark layer at embryo base; 12–14% moisture	Moisture 12–14%	35–40 days after anthesis (physiological maturity at 35%)
Chickpea	Dry brown pods; plant-wide yellowing	Seed moisture <16%	—

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Harvesting Methods

Manual Harvesting

• Harvesting by hand using scissors, pruning shears, knives, or stem-cutting clippers
• Advantages: selective harvesting at optimum maturity; minimal mechanical damage; essential for tender produce (strawberry, tomato, mango)
• Disadvantages: labour-intensive and expensive; prone to variability in quality

Mechanical Harvesting

• Combine harvesters: simultaneous cutting, threshing, and cleaning; wheat, rice, soybean, maize
• Tree shakers: trunk/limb shaking mechanism with catch frames; olives, almonds, walnuts, prunes
• Berry harvesters: flexible rods agitate canes to detach berries; blueberries, coffee
• Vine grape harvesters: rotating beaters; primarily for wine grapes; some crushing acceptable

Selective Picking

• Multiple harvest passes at intervals to pick only ripe produce
• Essential for mangoes, tomatoes, capsicum — where all fruits do not mature simultaneously
• Increases quality but raises harvesting cost 2–3×

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Post-Harvest Handling Operations

Sorting

Sorting is the separation of produce into acceptable and unacceptable categories, removing diseased, damaged, off-grade, or foreign material.

• Manual sorting: workers on conveyor belt inspect and remove defects; labour-intensive but flexible
• Machine vision sorting: cameras + AI algorithms detect colour, shape, surface defects at high speed (5–20 t/h); used for high-value produce (apple, tomato, potato)

Grading

Grading classifies acceptable produce into uniform lots by quality attributes (size, colour, weight, shape).

• Size grading: roller graders (spherical fruits), weight graders (electronic load cells), length graders (green beans)
• Colour grading: spectrophotometric colour sorters; citrus, tomato
• Weight grading: electronic load cells per fruit; apple, mango, pear — weight determines grade
• Grade designations: Grade A (premium/export), Grade B (good commercial), Grade C (processing/local markets)
• AGMARK grading: voluntary government grading certification; Grade A/B/C standards established by Directorate of Marketing and Inspection (DMI) for select commodities

Cleaning and Washing

• Remove field soil, surface contamination, latex, pesticide residues
• Brush washers: soft rotating brushes under water spray; citrus, apple, mango
• Flotation tanks: water + brush or paddle agitation; root vegetables
• Sanitisation: chlorinated water 100–200 ppm sodium hypochlorite (FSSAI permitted) to reduce microbial load; pH 6.5–7.5 for maximum efficacy
• Drying after washing: air knives, towelling, warm air tunnels — critical to prevent fungal growth

Pre-cooling

Pre-cooling is the rapid removal of field heat from freshly harvested produce before refrigerated storage or transport.

Method	Mechanism	Rate	Best Suited For
Forced air cooling	Cold air forced through carton vents	1–4 hours	Most fruits and vegetables
Hydrocooling	Immersion/flood with 1–2°C water	15–30 min	Corn, peach, carrot, celery
Vacuum cooling	Pressure reduction → evaporative cooling	20–30 min	Lettuce, mushroom, spinach, cut flowers
Room cooling	Cold room ambient	12–24 hours	Low-respiration commodities
Ice cooling	Crushed ice packed with produce	Hours	Broccoli, sweet corn, leafy greens

Vacuum cooling: fastest method for leafy produce; lettuce cooled from 25°C to 2°C in 30 minutes; expensive capital investment (₹80 lakh per unit).

Curing

Post-harvest treatment to promote wound healing and suberisation (formation of a protective cork layer) before storage.

Commodity	Temperature	Humidity	Duration	Purpose
Potato	13–16°C	90–95% RH	10–14 days	Suberisation of skin damage; reduces water loss
Sweet potato	29–32°C	85–90% RH	4–7 days	Wound healing; reduces decay
Onion	Ambient/low	60–70% RH	2–4 weeks	Outer skin drying; reduces neck rot
Cassava	30–40°C	High	2–3 days	Wound healing before storage

Surface Treatments

Wax coating: applied to reduce transpiration (water loss), improve appearance (sheen), and sometimes carry fungicide.

• Natural waxes: carnauba wax (Brazilian palm), shellac (lac insect), beeswax — approved by FSSAI for food use
• Synthetic waxes: paraffin, polyethylene wax (less preferred; food safety concerns)
• Rice bran wax: gaining acceptance; biodegradable
• Effect: reduces water loss by 30–50%; improves shelf life of citrus, apple, mango, capsicum
• Applied by brushing, dipping, or spray on grading lines after washing

Fungicide dips: Thiabendazole (TBZ), Imazalil — used in export mango/citrus; regulated by FSSAI and importing country MRLs (Maximum Residue Limits).

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Packaging for Fresh Produce

Key Packaging Types

• Corrugated Fibre Board (CFB) boxes: most common for fresh produce; ventilation holes (2–5% of box surface area essential for forced air cooling); standard 10 or 20 kg for mango; stacking strength critical
• Perforated polypropylene bags: fresh vegetables (beans, greens); moisture retention + gas exchange
• Foam net sleeves: cushioning for individual premium fruits (apple, pear, mango); prevents bruising
• Telescopic cartons (two-piece top-bottom): apple, pear — snug fit prevents movement
• Wooden crates: still used for bananas; heavy but allows airflow

Integrated Grading Lines

Modern packhouses use integrated systems combining: Washing → Drying → Sorting (machine vision) → Wax application → Grading (weight/colour) → Packing into cartons Capacity: 5–20 t/hour for apple; major brands: Unitec (Italy), MAF Roda (France/India)

GlobalG.A.P. Certification

• International standard for Good Agricultural Practice
• Mandatory for export to European supermarkets (Tesco, Carrefour, Metro)
• Covers food safety, traceability, environment, worker welfare
• Indian mango exporters: must have GlobalG.A.P. certification for EU market

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Summary Cheat Sheet

Topic	Key takeaway
Main focus	Maturity indices and harvesting standards for major crops; post-harvest handling operations including sorting, grading, pre-cooling, curing, and packaging.
Section context	Revise this lesson with the rest of Post-Harvest Basics for stronger conceptual continuity.