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Review for Exam #1

Outline

• Product deterioration

• Paper and paperboard

• Glass

• Metal

• Plastics

• Retortable pouch

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Product Deterioration

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Mechanisms of Product Deterioration

• Biological

• Enzymatic

• Physical

• Chemical

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Biological Mechanisms

• Microorganisms: Bacteria, molds, yeasts– Acid/alcohol/gas/pigment/toxin produced

– Can be pre-harvest or post-harvest decay

• Macroorganisms: Insects, parasites, rodents– Damage 5-10% of US grain crop

– Insects cause only minor damage, but allows for microbial invasion

– Rodents consume large quantity of food and contaminate with filth

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Enzymatic Mechanisms

• Enzymes: Large protein molecules that act as biological catalysts; activity is substrate specific and depends on temperature and pH

• Living tissue maintains enzyme balance– Harvest/slaughter disrupts pH & enzyme balance

– Enzyme activity becomes uncontrolled

– Can lead to tissue damage and spoilage

• Ascorbic acid oxidase, lipase, lipoxygenase, PPO, pectic enzymes, peroxidase, protease, thiaminase, PG

• Enzymatic browning: Reaction of O2 with O-dihydroxyphenol in presence of PPO to produce quinone

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Physical Mechanisms• Forces

– Bruising, crushing, wilting

• Light− Chlorophyll, anthocyanins, carotenoids, Vit. (B2, C) can be destroyed

− Discoloration of fresh meat

• Temperature− Rates of reactions generally double for every 10 °C temperature rise

− Protein denaturation, emulsion breakdown, dehydration could take place; this can result in textural changes

− Cold: Discoloration/texture change with freezing; chill injury for fruits

• Oxygen• Oxidation destroys Vit. A&C, alters color; off-flavors; mold growth

• Moisture• Lumping, caking, condensation, crystallization, stickiness

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Chemical Mechanisms• Auto-oxidation

− Unsaturated fatty acids are susceptible to autocatalytic breakdown in presence of oxygen Proceeds by free-radical chain reaction

Products formed can cause rancidity, color change, Vit. (A, C, E) destruction

• Maillard browning

• Lipid hydrolysis/oxidation

• Protein denaturation/hydrolysis

• Oligo/polysaccharide hydrolysis/oxidation

• Polysaccharide synthesis

• Degradation of natural pigments

• Glycolytic changes

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Paper and Paperboard

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Composition of Wood Pulp• Cellulose (~50%)

– Long chain, high molecular weight polymer of glucose

– Moderately resistant to chlorine and dilute NaOH

– Relatively resistant to oxidation with bleaching agents

• Hemicellulose (~20%)– Shorter chain, lower molecular weight polymers of xylose, mannose,

arabinose, galactose, and uronic acid

– Soluble in dilute alkali

– Its quantity and not chemical nature determines properties

– Responsible for hydration & bonding during beating of pulp

• Lignin (~30%)– Highly branched alkylaromatic thermoplastic polymer of substituted

phenyl-propane units

– Has no fiber-forming properties

– Attacked by Cl & NaOH & forms soluble, dark brown derivatives

– Softens at ~160 °C 10

Softwood and Hardwood

• Softwoods– Coniferous trees: Strong and rough paper

– Fibers: ~ 1/4” length

– Fiberboard, corrugated

• Hardwoods– Deciduous trees: Weak and fine paper

– Fibers: ~ 1/10” length

– Printing of labels

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Papermaking Operations

• Pulping

• Forming paper

• Pressing and drying

• Converting

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Goals of Pulping

• Remove all lignin (intercellular substance) to free the fibers– The more the lignin is retained, the less strong the paper

and faster it loses color and strength

• Keep some of the hemicellulose

• Keep all of the cellulose

• Separate the fibers without damaging them so that they can be formed into a sheet

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Pulping for Different Starting Materials

• Hardwood/softwood (mechanical): Debark, grind, wash & refine, bleach and/or color

• Hardwood/softwood (chemical): Debark, chip, digest, wash & refine, bleach and/or color

• Other plant material: Digest, wash & refine, bleach and/or color

• Waste paper: Wash & refine, bleach and/or color

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Types of Pulp

• Mechanical

• Chemical

• Semi-chemical

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Mechanical Pulp

• Force wood against rapidly revolving grindstone Groundwood pulp

• Groundwood pulp contains 70-80% fiber bundles, broken fibers, and fines in addition to individual fibers

• Higher yield than chemical pulp since lignin is also utilized

• Used for newsprint and magazine papers because of low cost and quick ink-absorbance (because of broken fibers)

• Used for folding cartons, wall papers, tissues

• High bulk, excellent opacity, low strength

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Chemical Pulp• Use high temperature and alkali to dissolve lignin

• High quality pulp, but only ~50% yield

• Generally, bark is removed for chemical pulping

• Alkaline processes– Soda process

• First chemical pulp process (1851)

• Boil wood in 4-6% by weight of NaOH @ 170 °C; not popular now

– Sulfate/Kraft process• Operator accidentally emptied vat before full cook

• Resulted in stronger paper; most popular method now

• Uses NaOH & Na2S; Na2SO4 is used as make-up chemical in recovery process

• Sulfite processes– Acid sulfite process

• Acidic liquor → Ca. Bisulfite and excess of SO2 is used

• Light colored pulp; easily bleached; not popular method, now

– Bisulfite process• Uses liquor of Mg or Ammonium Bisulfite & SO2; cook at pH of 4.0 17

Semi-Chemical Pulp

• Softening of wood chips with sulfurous acid or bisulfite followed by rubbing or grinding to produce pulp

• This is milder than the chemical process and hence hemicelluloses are retained to a greater extent, resulting in higher strength and yield

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Comparison of Pulping Processes

Mechanical Semi-chemical Chemical

Yield 90-95% 50-90% 40-55%

Fibers Short, impure Intermediate Long, pure, strong, stable

Print Good print quality

Intermediate Poor print quality

Bleaching Difficult Intermediate Easy

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Paper Manufacturing Process(Fourdrinier Machine)

• Named after its financiers (British)

• Continuous, horizontal, moving belt of fine wire mesh

• Deposit dilute suspension of fibers on screen

• 95% of water drained through wire

• Fibers interlay randomly

• Square grain (fiber alignment and hence strength in machine direction -- MD and cross direction -- CD are ~ same)

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Fourdrinier Machine

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Paper Manufacturing Process(Cylinder Machine)

• Cylinder covered with wire cloth rotated (partially submerged in suspension)

• Vacuum applied inside and so water drains inside and paper web forms outside

• Web is picked up by felt which is pressed by a roll

• Series of vats provide individual plies of fiber which are matted together

• Much stronger in MD than CD

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Cylinder Machine

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Properties of Paper(Basis Weight)

• Mass in grams per square meter (gsm)– Paper: ≤ 250 gsm

– Paperboard > 250 gsm

– Newsprint: 49

– Grocery bags: 49-98

– Kraft liner board: 127-439

– Folding box board: 195-586

• Also expressed as lbs per 1000 sq. ft. kg per 205 m2

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Properties of paper(Caliper or thickness)

• Thickness of single sheet measured under specific conditions– Newsprint: 85 m

– Linerboard: 230-640 m

• It is also expressed as mils– 1 mil = 1 point = 0.001 inch

– Paperboard: > 12 pts

– Corrugating medium: 9 pts

– Folding cartons: 15-30 pts

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Paperboard• Paperboard or board is defined by TAPPI as paper products with

basis weight > 250 gsm

• Chipboard– Made from recycled fibers on a cylinder machine

• Manila board– Made from virgin pulp and recycled fibers on cylinder machines

• Kraft Cylinder board– Made from virgin Kraft pulp and recycled Kraft fibers

• Kraft Fourdrinier board (Solid Bleached Sulfate Board)– Also called White Board or Food Board

– May be clay coated to give better printing surface

– May be waxed or polyethylene coated to give moisture resistance

– May be coated with PET for baking foods or reheating frozen foods

Note: It is unlawful to have direct contact between food and recycled paper fibers26

Cardboard Box• Liner

– Usually unbleached kraft

– Sulfate pulping of softwood on Fourdrinier machine

– 16 pts

– Basis wt = 42 lbs/1000 ft2

• Medium– Usually unbleached kraft

– Semi-chemical hardwood on Fourdrinier machine

– 9 pts

– Basis wt = 26 lbs/1000 ft2

• Glue– Corn starch

– Good bond, but insects like it 27

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Manufacture of Corrugated Board

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FlutesType Height (cm) # of flutes per m

A 0.47 110

B 0.246 154

C 0.361 138

E 0.114 315

• Flutes: Act like arches in resisting flat crush; act like columns and resist edge crush; trap air and give some insulation properties

• A → Max. cushioning and good top to bottom compression

• B → High resistance to flat crush

• C → Compromise of properties; widely used

• E → Like solid paperboard (cushions & insulates @ low weight)

Solid paperboard: Several layers of 0.13-0.33 mm paper to yield 0.8-2.8 mm (557-158 gsm) 29

Testing of Paper Products• Linerboard

– Bursting strength (Mullen tester)

– Basis weight

– Puncture resistance

– Stiffness

– Tear resistance

– Tensile strength

– Moisture content

– Water resistance

– Caliper

• Medium– Ring crush or stiffness test

• Corrugated board– Bursting strength, Edge compression, Flat crush, Pin adhesion

• Finished corrugated box– Puncture test, Compression, Drop test, Impact test

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Advantages and Disadvantages of Paper• Advantages

– Paper can provide a barrier to light

– Paper can be made into a variety of single wall bags (eg. grocery bags) and multi-wall bags (eg. flour, sugar)

– Paperboard provides strength & protection in many packages

– Paper and paperboard can be coated or laminated with wax, polyethylene or polyvinylchloride to improve moisture and gas barrier properties and allow sealability

– Only uncoated/unlaminated paper and paperboard can be recycled

• Disadvantages– Negligible moisture, gas or microorganism barrier properties when

not coated or laminated

– Not heat sealable unless coated or laminated

– Coated/laminated paper/paperboard are, in general, not recyclable31

Glass

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Types of Glass Containers• Bottles

– Beer, ketchup, salad dressing, vegetable oil, beverages, vinegar, wine

• Jars– Wide mouth containers for fruits, vegetables, jams,

preserves, instant coffee, coffee whiteners, baby foods

• Jugs– 1 gallon bottles with small neck, often with a carrying

handle -- institutional, industrial, and household products

• Carboys– 3-13 gallon capacity -- enclosed in a wooden overpack;

for drinking water, distilled water, and industrial use33

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Blow and Blow Bottle Making Process

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Press and Blow Bottle Making Process

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Types of Glass• Soda-lime glass

– Least expensive, chemically durable, most popular

– Soda, Na2O, potash, K2O dec. visc. below that of silica & helps use low melt temp. & improves “fining” (clearing up) qualities of glass

• Borosilicate glass– Use of B2O3 yields low thermal expansion coeff. (good thermal

shock resistance) and high chemical resistance

– B2O3 does not dec. visc. as much as soda; thus, high temp, cost

– Pyrex glass is a brand name for a type of borosilicate glass

• Lead silicate glass– Contains mainly PbO and SiO2

– PbO replaces lime (CaO) in the soda-lime process

– Lead inc. brilliance, expands working range (useful to make art objects & intricate shapes w/o freq. reheating), but dec. hardness

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Closures for Glass Containers

• Designed for internal pressure (200 - 800 kPa)– Crown cap or twist-off cap -- steel

– Roll-on or spin-on aluminum closure

• Designed for vacuum seal– Lug-type

– Twist cap

– Press-on twist-off cap

– Pry-off

• Designed only to contain materials in package– Screw top with minimum thread engagement

Metal closures: Screw caps, crowns, lug caps, spin-on or roll-on37

Advantages of Glass• Moderate cost

• Easily shaped and formed at high speeds

• Chemically durable

• Strong; survives all processing conditions

• Easily dispenses product

• Resealable

• Microwaveable, impermeable to gases & moisture

• Tasteless, odorless, transparent

• UV inhibitors can give protection from UV

• Numerous closure applications

• Recyclable 38

Disadvantages of Glass

• Breakable

• Heavy

• No anti-static agent to protect from dust

• Color limitations

• Secondary packaging limitations

• Cylindrical shape occupies excessive shape in storage

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Metal

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Metals Used in Food Packaging

• Aluminum (with small amounts of Mg & Mn)– For cans and foils

• Tin & Steel– Tinplate (for tin/steel cans)

• Chromium & Steel– Electrolytic chrome-coated steel (ECCS); also called Tin-

free steel (TFS)

• Lead & Copper– Used for soldering (Pb) or welding (Cu) of 3-piece

tinplate and ECCS containers41

Tin Free Steel (TFS)

1. Chemically passivated steel, which has a phosphate-chromate film on the surface

2. Chrome-coated steel with a layer of chromium oxide on top of the metallic chromium

3. Aluminum coated steel

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Tinplate and ECCS

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Types of Cans• Three-piece

– Soldered side seam (not used in the U.S. because of lead)• Exception: Lead-free solder used for canned asparagus

– Welded side seam (only method in U.S.)

• Two-piece (developed in the late 1970s)– Drawn & Ironed (D&I)

• Flat metal sheet is formed into a cup by a punch in a circular die

• Thickness of cup is uniform throughout

• Ironing dies in ironing press reduce thickness and increase height

• Wall is thinner than base

– Drawn & Redrawn (DRD)• Sequential drawing of cup into dies of smaller diameter

• Redistributes base to wall

• Wall & base thickness same as original sheet metal thickness

Advantages of two-piece method: Technical, economical, aesthetic44

Manufacture of Drawn and Ironed Can

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Manufacture of Drawn & Redrawn Can

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Manufacture of Three-Piece Cans

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Can Welding Process

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Can End/Lid

• The lid is double-seamed onto the body for both types of cans

• The expansion rings on the lid act as diaphragms– Expand during processing & return to original position

later (vacuum)

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Can End Embossing Pattern

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Profile of Can End

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Double Seaming Operation

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Main Components of a Double Seam

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Double Seam Terminology

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Aerosol Cans

• Developed by Dept. of Agriculture based on need for U.S. Army in 1942– To combat insects on Japanese islands during WW-II

• Thicker gauge steel can (or ECCS) than soup cans– To withstand pressure

• Interior is coated to withstand effects of propellant and product– Oleoresins, vinyl, acrylic, phenolic, and epoxy-phenolic

compounds

• Filling of container is through valve stem or under the dome

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Components inside Aerosol Containers

• Active ingredient (product)

• Propellants (provide pressure to force product out)– Volatile

• Blend of propane, butane, and isobutene

– Non-volatile propellants• CO2, N2, NO, air

• Solvent (brings product in solution with propellant)

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Advantages of Metal

• Strong

• Resistant to high heat and pressure

• Good barrier to light, oxygen, and moisture

• High speed can production (and product filling) possible

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Disadvantages of Metal

• Heavy– Transportation cost is high

• Can be difficult to open

• Cylindrical shape results in wastage of space during storage and transportation

• BPA concerns

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Plastics

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Monomers and Polymers• Monomer

– Ethylene (CH2 = CH2)

– Propylene (CH3-CH=CH2)

– Vinyl chloride (CH2=CHCl)

• Homopolymer– Polyethylene (PE), Polypropylene (PP), Polyvinylchloride (PVC)

• Copolymer (Eg., EVOH, LLDPE)– Random (ABAAABBBBABBA)

– Alternate (ABABAB)

– Block (AAAAABBBBB)

• Graft ( A- - -A- - -A

B B B

B B B)

• Combination (Some combination of above) 60

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Commonly Used Types of Plastics

1. Polyethyleneterephthalate (PET)

2. High density polyethylene (HDPE)

3. Polyvinylchloride (PVC)

4. Low density polyethylene (LDPE)

5. Polypropylene (PP)

6. Polystyrene (PS)

7. Other (Multilayer) – PC is included in this

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Crystalline and Amorphous Structures• Crystalline

– Long-range orderly structure• Ionically bonded: Solidification of salts from molten fluid or crystallization

from a solution

• Covalently bonded: Diamond, silica, graphite

– Polymorphism: Ability to exist in more than one crystal form (for pure elements, polymorphism is called allotropy; diamond, graphite, and fullerenes are allotropes of Carbon)

• Ice: Hexagonal, cubic, rhombohedral

– Polyamorphism: If amorphous phases are also present

• Polycrystalline (most metals and many ceramics)– Composed of crystals of different sizes oriented in diff. directions

• Amorphous (or vitreous or glass-like)– No long-range orderly structure

– Latent heat of fusion is not released during formation of glass 62

Films• Thickness less than 10 mils or 0.01”

• Laminate– Combining two or more films with an adhesive

• Composite– Combining two or more thin streams by co-extrusion

• Shrink film (PVDC, PVC)– Temperature range of shrinking, degree of shrinking, and

shrink tension are the 3 important parameters

• Stretch film (PE, LDPE, PVC, EVA, PP)– Stretchability, stress, re-stretch force, and breaking

strength are the 4 important parameters63

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Manufacture of Films

• Thermoplastic is extruded and converted into films by– Tubular (or blown) film

• Has an annular die ring that may be rotating to ensure uniform film thickness

• Air is blown into the tube to maintain the bubble

• Guide rolls, pinch rolls, wrap-up reel are downstream

– Flat film (or sheet film or cast film or slit die film)• Plastic is extruded through slit die

• Chilled rollers form the uniform thickness film

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Flat Film and Sheet Extrusion

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Tubular Film or Blown Film Extrusion

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Manufacture of Containers• Extrusion blow molding

– Single mold, handleware, large containers, co-extrusion possible; can not run PET, limited precision, trim scrap

• Injection molding

• Injection blow molding

• Injection stretch blow molding

• Thermoforming– Matched die (matched mold) forming

– Vacuum forming

– Pressure forming

– Ring and plug (press) forming67

Extrusion Blow Molding

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Injection Molding

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Injection Blow Molding

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Injection Stretch Blow Molding

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ThermoformingMatched die (matched mold) forming

Vacuum forming

Pressure forming

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Advantages of Plastic• Lightweight

• Durable (no rot or rust; only UV degrades it)

• Easy sealability

• Various shapes, handles, and spouts

• Light control & package appearance (clear to hazy)

• Easy to print and apply labels on

• Good strength

• Good tear resistance and puncture resistance– Better than paper, cellophane, Al foil

• Low temp. flexibility (cellophane embrittles @ 40 °F)73

Disadvantages of Plastic

• Migration/leaching

• Environmental concerns (landfill vs. recycling)

• Improving barrier properties increases cost

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Retortable Pouch

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Retortable Pouch (Overview)• It is a flexible package (also called stand-up pouch)

• Product is hermetically sealed in it just like in a can– Shelf life is comparable to that of a product in a can

• Use began in the 1950s with the military for MREs

• US Army Natick, Reynolds Metals Company, and Continental Flexible Packaging jointly received the 1978 IFT Industrial Achievement Award for it

• Product can be eaten cold or warmed by immersing pouch in hot water

• Sometimes, the pouches are placed in a cardboard box for aesthetic reasons or for puncture resistance Companies: Capri Sun, Star-Kist, Bumble Bee 76

Layers of a Retort Pouch

• Polypropylene (food contact surface)– Good heat seal surface, flexible, strong

• Aluminum foil– Barrier to O2, moisture, light, odor

– Stiffness permits tear-notch

• Nylon– Abrasion/puncture resistance

• Polyester– High temperature resistance, tough, printable surface

Note: The existence of 4 layers makes recycling difficult77

Types of Retort Pouches• Pre-formed

– 3 sides already sealed by pouch manufacturer

• In-line formed– Web-fed roll-stock, tensioning device (to smooth the surface),

web folding assembly (fold web in half), heat sealer (seal vertical sides), roller knife (separate individual pouches)

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Advantages of Retortable Pouch

• Easy to open unlike cans– Notch facilitates easy opening

• Less transportation cost– Lighter than a can and can be flattened

• Less storage space for empty containers

• Less over-cooking and hence better product quality– For same volume as a can, smallest dimension of pouch

is less than that for a can

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Disadvantages of Retortable Pouch

• Capital cost for new equipment is high– This is not a commonly used equipment and hence an

investment has to be made to procure it

• Thermal process is more complex– Where is the cold spot? How much air is remaining and

where is the air bubble?

• It is easily punctured– Secondary packaging may thus be needed

• Filling operation is slower than for cans

• Leak detection equipment (burst tester, tensile tester) is different

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