Food packaging

In short

Food packaging is the engineered system of materials and techniques that contains a food, protects it from moisture, oxygen, light, microbes, pests and mechanical damage, carries legally mandated information, and makes the product convenient to handle and sell. It is not an afterthought: for most processed foods the package, not the process, decides the shelf life, because it fixes the rate at which water vapour and oxygen reach the food. In Indian universities it is examined as material properties, barrier calculations, package–product interaction, packaging machinery and the FSSAI/BIS/Legal Metrology framework; in GATE-type and placement papers as permeability and shelf-life numericals. Employers who test it directly include Amul and other dairy federations, Britannia, Parle, ITC Foods, Nestlé India, Mother Dairy, Haldiram's, Dabur, Tetra Pak India, Uflex, Huhtamaki, Essel Propack, TCPL Packaging and Hindustan Tin Works, in roles such as packaging development, QA and production.

Explained

Functions, levels and classification

• Functions: containment; protection (barrier to moisture, gas, light, odour, microbes, insects, dust); preservation (holds the condition created by processing); communication (label, brand, legal declarations, barcode/QR); convenience (dispensing, reclosure, portioning, microwavability); unitisation for distribution.
• Levels: primary package touches the food (pouch, can, bottle); secondary groups primaries (carton, shrink-wrapped tray); tertiary/transport package for distribution (corrugated box, shrink-wrapped pallet).
• Rigid (metal cans, glass bottles, rigid plastic jars), semi-rigid (thermoformed cups, aluminium trays, folding cartons), flexible (films, foils, laminates, pouches).
• Hermetic (gas- and microbe-tight: can, glass with sealed closure, sealed laminate) versus non-hermetic (paper wrap, net bag, perforated film for fresh produce that must breathe).
• Aseptic packaging = commercially sterile product filled into a sterile package in a sterile zone and hermetically sealed; retortable packaging = product filled, sealed and then heat-sterilised inside the pack.

Metal, glass and paper

• Tinplate: low-carbon mild steel base (0.15–0.30 mm) electrolytically coated with tin; a can is designated by coating mass such as E 2.8/2.8, meaning 2.8 g of tin per m² on each face. Build-up: steel – tin – tin-oxide – passivation – oil film – (lacquer).
• Lacquers (enamels): epoxy-phenolic (general, acid foods), oleoresinous (fruit), sulphur-resistant zinc-oxide enamel for peas, corn, fish and meat to stop black sulphide staining; organosol/vinyl for beer and drawn cans. Modern lines increasingly use BPA-non-intent (BPA-NI) coatings.
• Can defects: sulphide staining (cosmetic), hydrogen swell (acid attack on steel generating H₂ — a chemical, not microbial, swell), springer, flipper, buckle, pinholing, detinning.
• Construction: 3-piece (body + two ends, side seam welded, ends joined by double seam) and 2-piece (drawn, DRD or DWI — beverage cans). Tin-free steel (TFS/ECCS) is chrome-coated and must always be lacquered. Can sizes are quoted as three-digit numbers: 307 × 409 = 3 7/16 in diameter × 4 9/16 in height.
• Double seam interlocks five thicknesses of metal with a sealing compound; QA measures seam thickness, width, countersink depth, body hook, cover hook, overlap and % body-hook butting — a double-seam teardown is routine QC in any cannery.
• Aluminium: foil 6–9 µm has pinholes (not a total barrier), ≥25 µm is effectively a total barrier to gas, moisture, light; used as a laminate ply, semi-rigid trays, beverage cans and easy-open ends. Not for strongly acid or alkaline foods unless lacquered.
• Glass: inert, impermeable, transparent, reusable, microwavable; heavy and brittle. Type I borosilicate (high thermal shock resistance), Type II surface-treated soda-lime, Type III ordinary soda-lime (most food bottles). Made by blow-and-blow (narrow neck) or press-and-blow (wide mouth), then annealed in a lehr to remove stress; amber/green glass screens UV for beer and oils.
• Closures: crown cork (carbonated drinks), ROPP aluminium (liquor, syrups), lug cap and press-on twist-off (PT) for vacuum-packed jams/pickles, continuous-thread caps, induction-sealed wads for tamper evidence.
• Paper and board: quantified by GSM (g/m²) and caliper. Kraft (strong), greaseproof and glassine (hydrated, grease-resistant), vegetable parchment (wet strength, butter/ghee), MG/MF papers, waxed paper. Board: duplex/triplex folding cartons, corrugated fibreboard (single/double/triple wall; flutes A, B, C, E/F micro-flute) tested by bursting strength, ECT (edge crush) and BCT (box compression). Paper alone is not a moisture or gas barrier — it is coated, waxed, laminated or metallised.

Plastics and laminates

• Polyolefins: LDPE/LLDPE — cheap, excellent heat-seal, good moisture barrier, poor gas barrier (milk pouches, liners); HDPE — stiffer, better moisture barrier, opaque (crates, bottles, grocery film); PP — high melting point (~160 °C), hot-fill and microwavable, BOPP (biaxially oriented, printable, stiff — biscuit and snack wraps), CPP (cast, good sealant layer, retort grade available).
• Polyesters: PET — strong, clear, good gas and aroma barrier, basis of carbonated drink and edible-oil bottles; metallised PET gives light plus high gas barrier at low cost.
• High gas barriers: EVOH (best O₂ barrier but moisture-sensitive, so buried between polyolefin plies), PVDC (barrier to both O₂ and moisture, also used as coating), PA/nylon (good O₂ barrier, tough, thermoformable).
• Others: PS and EPS (cups, trays, curd cups), PVC (cling film, blister), PC (water jars), ionomer (Surlyn) as a tough seal layer through contamination.
• Why laminate: no single polymer gives print quality + barrier + sealability + stiffness. Typical structures — snacks: BOPP/metallised BOPP or PET/met-PET/LDPE; retort pouch: PET 12 µm / Al foil 9–12 µm / (nylon) / CPP 70–80 µm; liquid carton (UHT milk): paperboard with polyethylene inside and out and an aluminium foil ply — about 70–75% paper, ~20% PE, ~5% Al; milk pouch: 3-layer co-extruded LDPE/LLDPE blend, typically 50–60 µm, with carbon black/TiO₂ for light protection.
• Conversion processes: extrusion and co-extrusion, blown/cast film, extrusion and adhesive lamination, metallising (vacuum-deposited Al ~400 Å), blow moulding, injection moulding, thermoforming, form-fill-seal (VFFS for pouches, HFFS for trays).
• Biodegradable and edible: PLA, PHA, starch blends, bagasse moulded ware, paper straws (pushed by the single-use plastic ban); edible films/coatings of zein, gluten, chitosan, alginate, shellac and wax — mainly a barrier booster, not a stand-alone package.

Barrier properties and package testing

• WVTR / MVTR: g of water vapour per m² per 24 h at a stated condition (commonly 38 °C, 90% RH, 1 atm) — always quote the condition, the value is meaningless without it.
• OTR / GTR: cm³ (or cc) of O₂ per m² per 24 h at 1 atm (commonly 23 °C, 0% or 50% RH); permeability multiplies this by thickness so it describes the material, not the sheet.
• Migration: transfer of package constituents (monomers, plasticisers, catalysts, inks) into food. Overall migration limit is 60 mg/kg of food (or 10 mg/dm² of surface) tested per the BIS migration method (IS 9845) using simulants — distilled water, 3% acetic acid, 10–50% ethanol, n-heptane/olive oil — at time–temperature conditions matching use. Specific migration limits apply to named substances.
• Other tests: seal strength and hot-tack, dye-penetration and vacuum/bubble leak test for seal integrity, tensile and elongation, dart impact, puncture resistance, COF (slip), gloss/haze, bond strength of lamination, ink rub/scuff and scratch resistance, grease resistance (KIT test), drop and vibration tests (ISTA-type), box compression, light transmission, bursting strength, scalping (aroma pickup by the polymer).
• Headspace gas analysis confirms MAP mix and residual O₂; shelf-life studies run real-time plus accelerated (higher T and RH) conditions.

Packaging technologies that extend shelf life

• Vacuum packaging: air removed, pack collapsed onto product; stops oxidative rancidity and aerobic spoilage (ghee, meat, cheese, dry fruits). Risk: favours anaerobes, so chilling plus pH/aw control is essential; vacuum-skin and shrink bags for primal meat cuts.
• MAP: air replaced by a chosen mix — typically high CO₂ + N₂ for cooked meat, fish and bakery; high O₂ (~70–80% O₂ with ~20–30% CO₂) for fresh red meat colour; low O₂ + CO₂ for fresh produce. CO₂ inhibits microbes and dissolves in the food; N₂ is an inert filler that prevents pack collapse; O₂ is normally minimised (but kept non-zero for fresh respiring produce and to avoid *Clostridium botulinum* risk in fish).
• Nitrogen flushing of snack packs (residual O₂ usually held below ~2%) also cushions the chips.
• EMAP for fruits and vegetables: a perforated or selectively permeable film balances the produce's respiration against film permeability so a steady atmosphere (e.g. 3–5% O₂, 5–10% CO₂) establishes itself. Wrong film → anaerobic off-flavours.
• Aseptic/UHT packaging: carton web or pre-formed pack sterilised with H₂O₂ plus heat or peroxide/UV, filled and sealed in a sterile chamber — gives ambient shelf life of several months for milk, juices and purees.
• Retort pouch: thin profile means faster heat penetration than a can, lighter weight, less storage space, ready-to-eat Indian curries and military rations; needs careful seal QC and secondary cartoning.
• Active packaging interacts deliberately: iron-based O₂ scavengers, CO₂ emitters/absorbers, ethylene absorbers (KMnO₄ on alumina) for fruit, silica gel and clay desiccants, moisture-absorbing pads in meat trays, antimicrobial films, antioxidant-releasing films.
• Intelligent/smart packaging only informs: time–temperature indicators, O₂/leak indicators, freshness (amine/CO₂) indicators, RFID and QR traceability, tamper-evident and child-resistant features.
• Other forms: shrink and stretch wrapping, skin packaging, blister/strip, aerosol, bag-in-box (edible oil, wine, juice concentrate), tetrahedral and gable-top cartons, PET and HDPE preform-blown bottles, collapsible tubes.

Package–product interaction and shelf-life prediction

• Moisture-sensitive foods (biscuits, namkeen, milk powder, spices) fail by moisture gain and loss of crispness/caking; a critical moisture content derived from the sorption isotherm defines end of shelf life. High-moisture foods (bread, cake, fresh produce) fail by moisture loss.
• Oxygen-sensitive foods (oils, fried snacks, ghee, nuts, milk powder, ground coffee) fail by oxidative rancidity — needs high-barrier, often metallised or foil structures plus N₂ or a scavenger.
• Light-sensitive foods: milk (riboflavin loss, light-oxidised flavour), oils, beer — hence opaque pouches, pigmented films, amber glass.
• Shelf life is computed by equating the permissible change to the quantity transmitted by the package: a steady-state WVTR estimate for a rough answer, and the integrated (logarithmic) form when the water activity inside rises appreciably and the driving force falls.
• Also considered: aroma scalping by polyolefins, odour pickup from inks and adhesives, corrosion of metal by acid foods, pest resistance (insects bore through single-layer films), and vibration/compression damage in transit.

Indian regulations, labelling and waste rules

• Food Safety and Standards Act, 2006 with the Food Safety and Standards (Packaging) Regulations, 2018 — the governing rule: packaging material must be of food grade, must comply with the listed BIS specifications, recycled plastic is not permitted in direct contact with food (FSSAI has since allowed recycled PET subject to notified conditions — verify the current amendment), printing ink must not come in contact with the food, and newspaper or similar printed paper must not be used for wrapping, covering or packing food. Overall migration 60 mg/kg; specific migration limits in the schedules.
• BIS specifications commonly cited (numbers and editions are revised, so confirm the current version): polyethylene for food contact (IS 10146), polypropylene (IS 10910), polyalkylene terephthalates/PET (IS 12252), styrene polymers (IS 10142), PVC (IS 10151), nylon (IS 12247), overall migration method (IS 9845), code of practice for printing inks for food packaging (IS 15495). Packaged drinking water and mineral water are under mandatory BIS certification.
• FSS (Labelling and Display) Regulations, 2020: FSSAI logo with licence number, name and complete address of manufacturer/packer, common/generic name, list of ingredients in descending order, declared allergens, nutritional information per 100 g/100 ml (and per serve with %RDA), veg (green) / non-veg (brown) symbol, net quantity, lot/batch number, date of manufacture and best before / use by, country of origin for imports, storage and use instructions, vegetarian logo for added flavours, and declaration for added colours/flavours and irradiated food.
• Legal Metrology (Packaged Commodities) Rules, 2011: net quantity in SI units, MRP inclusive of all taxes, month and year of manufacture/packing/import, consumer care contact, unit sale price, and the principal display panel size and character-height rules; errors in net content are policed as maximum permissible error.
• Waste side: Plastic Waste Management Rules, 2016 as amended — ban on identified single-use plastic items from 1 July 2022, minimum thickness of plastic carry bags raised to 120 µm, Extended Producer Responsibility (EPR) registration and targets for brand owners on collection, recycling and mandatory recycled content in rigid and flexible categories (targets are phased year-wise; check the latest CPCB guideline). Multilayer laminates are the hardest flexible waste stream to recycle, driving the industry shift to mono-material PE/PP recyclable laminates.
• Also relevant: AGMARK grade packaging for agricultural produce, Export Inspection Council requirements for export packs, and FSSAI's licensing of the food business rather than of the packaging converter.

Key points

• Primary/secondary/tertiary – food-contact pack, grouping pack, transport pack.
• Barrier – a package's rate of letting moisture (WVTR) and gas (OTR) through; it, not the process, usually sets shelf life.
• Permeability vs permeance – permeability includes thickness (material property); permeance/transmission rate is for the sheet as supplied.
• Hermetic seal – gas- and microorganism-tight; only a can, glass-with-closure or a properly sealed laminate qualifies.
• E 2.8/2.8 tinplate – 2.8 g/m² of tin per surface; sulphur-resistant enamel prevents black staining in peas, fish and meat.
• Double seam – five-thickness interlock of body and end flanges with sealing compound; measured by overlap and body-hook butting.
• Hydrogen swell – non-microbial can swell from acid attack on steel, distinct from bacterial spoilage swell.
• Glass types – I borosilicate, II treated soda-lime, III soda-lime; annealing removes stress; amber blocks UV.
• GSM and ECT – paper basis weight and corrugated edge crush, the inputs to box compression strength.
• LDPE seals well and blocks moisture but not oxygen; EVOH and PVDC block oxygen; PET gives strength and clarity; foil over 25 µm blocks everything.
• Laminate – layers chosen for print, barrier, strength and sealant; retort pouch = PET/Al/CPP.
• MAP – CO₂ inhibits microbes, N₂ fills, O₂ minimised except for respiring produce; verified by headspace analysis.
• Aseptic – sterile product + sterile package + sterile zone, giving ambient shelf life (UHT milk, juices).
• Active vs intelligent – active changes the pack environment (scavenger, absorber); intelligent only reports it (TTI, leak indicator).
• Critical moisture content – moisture level from the sorption isotherm at which the food becomes unacceptable; the target of shelf-life calculations.
• Overall migration limit 60 mg/kg of food, tested with simulants; recycled plastic generally barred from direct food contact.
• Mandatory on an Indian label – FSSAI logo and licence number, veg/non-veg mark, allergens, net quantity, MRP inclusive of taxes, date marking, batch number.
• EPR under PWM Rules – brand owners must collect and recycle their packaging and meet recycled-content targets; single-use plastic items banned since 1 July 2022.

Formulas and examples

Example 1 — Simple WVTR shelf life of a biscuit pack. 200 g biscuits at 2.0% moisture (dry basis), critical 5.0%; pack area 0.06 m²; BOPP/LDPE laminate WVTR 5 g/m²/day at 38 °C/90% RH.

• Dry solids = 200 / 1.02 ≈ 196 g.
• Permissible gain = 196 × (0.05 − 0.02) = 5.88 g.
• Ingress rate = 5 × 0.06 = 0.30 g/day.
• t = 5.88 / 0.30 ≈ 19.6 ≈ 20 days (conservative, because the real driving force falls as the pack humidifies).

Example 2 — Permeability from a cell test. 12 cm³ O₂ passes through a 50 µm film of area 100 cm² in 10 days with Δp = 0.21 atm (air on one side, N₂ on the other).

• A = 0.01 m²; OTR = 12 / (0.01 × 10 × 0.21) ≈ 571 cm³/(m²·day·atm).
• P = OTR × x = 571 × 50 ≈ 2.86 × 10⁴ cm³·µm/(m²·day·atm) — a poor barrier, unsuitable for fried snacks.

Example 3 — Integrated equation for a snack pack. Wₛ = 40 g solids, A = 0.04 m², permeance k/x = 0.05 g/(m²·day·mmHg), storage 25 °C and 65% RH so pₛ = 23.76 mmHg, isotherm slope b = 0.15 g/g per a_w, mᵢ = 0.02, m_c = 0.06, mₑ = 0.10 g/g solid.

• ln[(0.10 − 0.02)/(0.10 − 0.06)] = ln 2 = 0.693.
• Right-hand coefficient = 0.05 × (0.04/40) × (23.76/0.15) = 0.05 × 0.001 × 158.4 = 0.00792 per day.
• t = 0.693 / 0.00792 ≈ 87.5 ≈ 88 days. Halving the permeance to 0.025 doubles it to ~175 days.

Example 4 — MAP mix and film cost of a milk pouch. (a) Tray pack of total volume 1,000 ml holding 400 g of paneer (≈400 ml): headspace = 600 ml, G/P = 600/400 = 1.5; for a 70:30 CO₂:N₂ mix, CO₂ = 420 ml, N₂ = 180 ml. (b) A 500 ml milk pouch uses 0.05 m² (= 500 cm²) of 55 µm LDPE film, density 0.92 g/cm³.

• Film volume = 500 cm² × 0.0055 cm = 2.75 cm³ → mass = 2.75 × 0.92 ≈ 2.53 g.
• At ₹160/kg, film cost ≈ 2.53 × 0.16 ≈ ₹0.40 per pouch.
• Yield = 1/(55 × 10⁻⁶ × 920) ≈ 19.8 m²/kg, so 1 kg of film makes about 19.8/0.05 ≈ 396 pouches.

Example 5 — Stacking height of a corrugated box. Box 400 × 300 mm, caliper 4.5 mm, ECT 6.0 kN/m, each filled box weighs 10 kg.

• Z = 2(0.4 + 0.3) = 1.4 m; √(0.0045 × 1.4) = √0.0063 = 0.0794.
• BCT = 5.87 × 6.0 × 0.0794 ≈ 2.80 kN ≈ 285 kgf.
• Safe load = 285/5 = 57 kgf → 57/10 ≈ 5 boxes may be stacked above the bottom box, i.e. a 6-high stack.

Where it is used

• Dairy: 500 ml milk pouches on VFFS lines, curd and lassi cups with foil lids, UHT milk and tetra-pack flavoured milk at Amul, Mother Dairy, Nandini, Hatsun; ghee in tinplate and laminated pouches.
• Snacks and bakery: N₂-flushed metallised laminates for chips and extruded snacks, BOPP wraps for biscuits, MAP for bread and cake rusk — Haldiram's, Bikaji, Britannia, Parle, ITC.
• Fruit and vegetable processing: aseptic bag-in-drum mango pulp for export, PET bottles and tetra cartons for juices and nectars, retortable pouches for curries and RTE meals (ITC Kitchens of India, MTR, Gits), EMAP punnets for grapes and pomegranate exports.
• Fish, meat and poultry: vacuum skin packs and high-CO₂ MAP trays for chilled cuts, EPS boxes with gel packs for cold-chain shipment (Licious, Suguna, Venky's).
• Job roles: packaging development executive (specification, structure design, vendor qualification), QA analyst (seam teardown, seal strength, migration and leak tests), production/packing line engineer (FFS, capper, filler efficiency, OEE), regulatory and labelling officer (FSSAI/Legal Metrology artwork approval), sustainability/EPR compliance officer.
• Converters and suppliers: Uflex, Huhtamaki India, Jindal Poly Films, Essel Propack, TCPL Packaging, Hindustan Tin Works, Tetra Pak India, Hindustan National Glass and Tirupati-based flexible units — all recruit food technology graduates for food-contact material development and testing.

Interview questions

• Q: Why is the package the main determinant of shelf life for a dry snack? A: Because processing only sets the starting condition; from then on, quality loss rate depends on how fast moisture and oxygen enter, which is fixed by the laminate's WVTR and OTR and the pack area-to-weight ratio.
• Q: Difference between WVTR and water vapour permeability? A: WVTR is the quantity per unit area per day for the film as it is (thickness included), while permeability is normalised for thickness and driving force, so it is a property of the material.
• Q: Why is EVOH never the outer layer of a laminate? A: Its oxygen barrier collapses when it picks up moisture, so it is sandwiched between polyolefin layers that keep it dry.
• Q: Which gases go into a MAP pack for fresh red meat and why? A: High O₂ (around 70–80%) with CO₂ to keep oxymyoglobin red while CO₂ suppresses microbial growth; for pre-cooked or fatty products the opposite — high CO₂ with N₂ and minimal O₂.
• Q: What is the food-safety risk of vacuum packaging? A: Removing oxygen selects for anaerobes, including *Clostridium botulinum*, so vacuum packs must additionally be controlled by chilling, pH, salt, nitrite or a_w.
• Q: Why is a sulphur-resistant enamel used for canned peas and fish? A: Sulphur compounds released on heating react with tin and iron to form black sulphides; the zinc-oxide-bearing enamel blocks that reaction, which is cosmetic but rejected by consumers.
• Q: Hydrogen swell versus microbial swell in a can — how do you tell them apart? A: Both bulge; hydrogen swell comes from acid corroding the steel, with normal odour, normal pH and no organisms on culture, while microbial swell shows gas plus off-odour and a positive microbiological test.
• Q: Why is a retort pouch preferred over a can for ready-to-eat curry? A: Its thin profile cuts heat-penetration time and thermal damage, it is lighter and cheaper to transport, and it reheats faster; the trade-off is seal-integrity sensitivity and the need for a secondary carton.
• Q: Can recycled plastic be used for food contact in India? A: Under the FSS (Packaging) Regulations, 2018 recycled plastic is not permitted in direct contact with food; recycled PET has since been allowed under specific notified conditions, so the current amendment must be checked before specifying it.
• Q: What is the overall migration limit and how is it tested? A: 60 mg per kg of food (or 10 mg/dm² of contact area), tested by exposing the material to simulants — water, 3% acetic acid, ethanol, oil/heptane — at time–temperature conditions matching actual use, following the BIS migration method.
• Q: What declarations must appear on a packaged food label in India? A: FSSAI logo with licence number, veg/non-veg symbol, name, ingredient list with allergens, nutrition panel, net quantity, MRP inclusive of all taxes, lot/batch number, date of manufacture and best-before/use-by, and manufacturer's full address with consumer care details.
• Q: How has the Plastic Waste Management framework changed packaging design? A: EPR targets and recycled-content obligations, the 120 µm carry-bag thickness rule and the single-use plastic ban have pushed brands from non-recyclable multilayer laminates to mono-material PE or PP structures and to paper and moulded fibre alternatives.

Common mistakes

• Quoting a WVTR or OTR without its temperature and RH, or comparing values measured at different conditions.
• Using the simple Δm = WVTR × A × t formula when the internal a_w rises a lot — it over-predicts ingress and under-predicts shelf life; the logarithmic form is needed.
• Unit slips: cm² against m², µm against m, wet-basis against dry-basis moisture, or forgetting that WVTR is per 24 h.
• Treating thin aluminium foil (6–9 µm) as an absolute barrier — it has pinholes and flex cracks, which is why it is always laminated.
• Claiming nitrogen "preserves" the food; N₂ is inert filler, CO₂ does the microbial inhibition and the real gain is removing O₂.
• Confusing active with intelligent packaging, or calling a desiccant sachet "intelligent".
• Saying a swollen can is always microbial spoilage, or forgetting that printing ink must not contact the food and that newspaper wrapping is prohibited.

Related topics

Food preservation methods · Market milk processing: pasteurisation and UHT · Fruit and vegetable processing · Beverage technology · Food quality control and sensory evaluation · Food laws, FSSAI standards and HACCP