Packaging

Function of packaging

A pack is more than just a means of conveniently and safely conveying biscuits to the consumer. It also allows the display of information about type, weight, contents, manufacture, price, age, etc. which may be required by law, and other more artistic attributes associated with customer appeal aimed at tempting sale or permitted easy recognition. The shape of the pack also has a bearing on the way in which it can be displayed on the shop shelf. Round column packs tend to roll off, packs with fin end seals tend to interlock with adjacent packs, simple bags cannot be piled well for display and block-bottom bags allow only one layer of packs to be put on the shelf.

Collation

The main function of a pack is to collate the correct weight or number of biscuits for sale. The biscuits may be single in a pack, in a single column, in a series of short columns side by side, in a jumble or in some other less common arrangement.

Customers tend to associate firm tight wraps with biscuits, feeling perhaps that floppy film packs may contain broken product. Packages with polypropylene film used as a single wrap will not feel so firm as those with multi-ply wraps of paper or Cellophane. It may be that both forms of packaging afford adequate and equal protection and hence the fears of the consumer are unfounded, but a skill of marketing is to avoid subconscious doubts from customers.

Labelling

A very high proportion of biscuits is bought on impulse so it is important that the design and colour of the packet is attractive and sufficiently descriptive of the contents. Legislation is becoming more demanding and considerable amounts of essential information have to be displayed in a clearly readable form. This can detract from those design aspects which may be deemed attractive.

Many markets are demanding that "sell by" or "best before" dates are printed on every pack to reassure customers that the product will be safe and pleasant to eat.

Protection against deterioration

Deterioration in the eating and visual qualities of biscuits is in the form of moisture pick up (in a very few cases moisture loss), rancidity and development of off flavours. There will also be deterioration if insects invade the pack but this problem is secondary to the others mentioned.

The barrier which prevents moisture pick up by the biscuits from the atmosphere will also be adequate for hygiene aspects. Plastic (polypropylene), plastic coated papers, or various laminates can be used to form the moisture barrier. They are usually heat sealable and this is how the pack is closed on the wrapping machine. The barrier properties are a combination of the basic moistureproofness of the materials used and the effectiveness of the seals. Tests for moistureproofness form a significant part of shelf life testing.

Flavour change is mostly due to chemical reactions in the ingredients particularly the fats. Oxidation of fats results in rancidity and this is greatly promoted by light, particularly ultra violet light. The packaging materials can retard the effects of chemical change by excluding (or reducing) the intensity of light and by excluding oxygen.

Biscuits are very susceptible to the pick up of strong odours and even small traces can spoil their flavour. Plastic and paper based wrappers are not particularly good barriers against aromatic chemicals so biscuits should not be stored near detergents, antiseptics or perfumed products.

Mechanical protection

Biscuits are typically very fragile and lose much of their appeal if broken. A tight group of biscuits affords much self protection but aids to rigidity, such as specially formed trays, base cards or folds of corrugated paper reduce the chance of breakage as a result of vibration or knocks in the life of the pack. Some biscuits have sharp edges or rough abrasive surfaces due to sugar, etc. and the packaging materials must be chosen to cope with these.

4cb-Corrugated-sleeves-thumCorrugated sleeves to enclose piles of biscuits in an envelope fold pack

Packs of biscuits are normally collated into groups of 6, 12 or more in boxes or shrink wraps for stacking, storage and transportation. These larger groups, if well packaged increase the protection to mechanical damage that the biscuits in the primary packs can have before they reach the consumer. However if the outer packaging is not good the act of stacking can cause damage.

Packaging materials

The materials used to package biscuits are most important and should be chosen and handled with care.

Packing and wrapping materials are such large industries that it is a problem to keep up to date with useful developments even in the relatively narrow field of biscuits. The following descriptions and comments should be regarded as basic information against which requirements, new claims and results of tests may be compared.

The cost of wrapping materials, when printing and wastage is included, is very considerable. As much care should be given to selection, handling and testing of these materials as is given to other ingredients used for making the biscuits.

Flexible films that are heat sealable and moistureproof

These are of two basic types of heat sealable and moistureproof packaging films, one is made from regenerated cellulose and the other is completely plastic based, usually polypropylene. The cellulose films, which are a form of transparent paper, must be coated with a moistureproof barrier but the plastic types are barriers in their own right even though they may also be coated. Aluminium foil should also be included in this group but at the thickness when it is truly flexible it is too thin to be a good moisture barrier because pinholes are formed. When aluminium foil is laminated with paper or plastic, it does perform extremely well as a packaging material.

Moistureproofness is measured by the rate that moisture vapour passes across the film barrier when it separates an atmosphere of given humidity from one of zero humidity at a given temperature.

There are two standard test conditions known as (a) temperate (relative humidity of 75% at 25°C) and (b) tropical (relative humidity of 90% at 38°C).

Specifications for films should give the water vapour permeability (wvp) or water vapour transmission rate (wvtr) as g/m2/24 hours at one of the two standards given above. The important point to remember is that the performance may be affected if the film is creased or printed and the specification relates to flat basic film. In terms of the overall pack the performance is also usually affected by the quality of the seals.

Gas permeability properties (for example for oxygen) are specified in cm3/m2/24 hours/atm at 23±1°C. Although the gas permeability may not be well related to the wvp and also varies considerably for different gases, it is not normally felt necessary to check this property of films for biscuit wrapping.

The films must have good heat sealing properties because the seals compliment the basic film properties in the performance of the pack. Although a pack may be sealed in various ways, modern packaging machinery is normally designed to make the seal by the application of heat and pressure. The sealing jaws apply the pressure and usually the heat, and sometimes the cutting action also. The temperature required to form the seal depends on:

  • the materials forming the seal;
  • the dwell time between the jaws, and
  • the pressure exerted by the jaws.

By controlling these conditions it is possible to check the seal performance of films by measuring the force needed to pull apart a seal on a given width of film.

Heat sealability at short dwell times is very critical and is most important on high speed wrapping machines. It is affected by several factors of which the main ones are:

  • The temperature control of the seal jaws.
  • The moisture content of the film, in the case of cellulose films.
  • The surface condition of the jaws and the jaw release properties of the film being sealed.

The heat seal is a weld of heat activated adhesives or in the case of plastic films may be a weld of the basic material. The seal strength is related to the amount of contact in the seal (affected by the pressure in the seal area) and also the anchoring of the thermosensitive material on the basic film.

Other properties which are important for flexible films are:

  • The slip properties (enabling it to "flow" over the various forming parts of the wrapping machine).
  • The tensile strength - usually related to the thickness of the material.
  • The brittleness - determining the tendency to crack under conditions of flexing at different temperatures and humidities.
  • The degree of ink keying on printed films. This can best be checked by applying a piece of Sellotape and seeing if the ink comes away when the tape is peeled off.

Against this background of basic performance requirements it is possible to compare the various films available. The following lists the main types.

Regenerated Cellulose films

These are made from wood pulp and are completely transparent but they can be coloured or rendered opaque by the addition of pigments. The most well-known brand name is Cellophane and previously these types of film were the most widely used in biscuit packaging. The lower cost of polypropylene films has meant that cellulose based films are now more or less displaced.

They are available in various thicknesses ranging from about 0.06-1.5 mm with that at about 0.08 mm being the most commonly used for biscuit wrapping.

Plastic films

Polyethylene films do not have sufficiently good wvp values for biscuit wrapping. Polypropylene film is much superior and in its various forms is widely used for biscuits. It is available as "cast", "biaxially orientated" and co extruded. In recent years the price and technical performance of polypropylene films have become so favourable that most biscuit manufacturers have discontinued using cellulose films. Only those with older packaging machines with poor heat controls on the sealers will want to continue to use cellulose. Unlike cellulose film which has good dimensional stability because it is a type of paper, plastic films become oriented as they are cast and have tendencies to shrink differentially in the two dimensions. Techniques have been developed to effectively control the orientations in each direction so that the machine handling, shrinkages when sealed, and tear strength are suitable for wrapping operations. Most polypropylene films used for biscuit packaging are orientated polypropylene, referred to as OPP films. Polypropylene is a naturally good moisture barrier and its strength is such that to achieve similar performance to coated cellulose films it can be used at much thinner gauge (giving improved yields) at very competitive prices. Plastic films are also made from other base materials, but they are not used to any significant degree for biscuit moistureproof wrapping. Plastic films are not governed by the need for such careful storage as cellulose films. They are not affected by moisture or normal ambient temperatures and can be stored for long periods.

Metallised films

Many of the advantages of aluminium foil laminates can be achieved more economically by using metallised cellulose or OPP film. This material comprises a PVdC coated film which has been metallised on one surface by vacuum deposition of high purity aluminium. The appearance is of aluminium foil, but the film has the flexibility, strength and thickness of the base film. If the metallised film is not laminated to another film or specially coated on the metallised side it can be heat sealed only on the non-metallised surface. The colour of the metallised surface can also be tinted with heat resistant gloss lacquers. The wvp properties are the same or slightly better than the base film. The oxygen permeability is significantly lower than the base film and this, plus the light excluding properties, is the main technical advantage of metallised films.

Laminates

Great improvements on nearly all the film properties described for the various base films may be achieved by combining two or more sheets of material to form laminates. The variety of combinations possible is very great and thus is impossible to describe concisely. For example paper, OPP, polyethylene, aluminium foil, metallised films and even thick card may be combined. Usually only two materials are laminated together but sometimes more may be used. Laminating permits the sandwiching of a printed surface so that a high gloss is displayed or the printing ink is protected. The converting (printing and sandwiching) process is expensive so laminates should always be considered against the costs and disadvantages of single films.

Aluminium foil

This is pure aluminium which is rolled to thicknesses as low as 0.006 mm. It offers particular advantages for packaging as it is a complete barrier to light, moisture, grease and gas provided that it does not have any pinholes. It also has excellent dead fold properties, which means that as you fold it, it does not have the tendency to spring back. The flexibility is not very good until it is very thin and then it does not have good tensile strength either. It is possible to roll aluminium without pinholing to about 0.03 mm and this is rather too thick and expensive for use around biscuits so the principle use of aluminium foil in packaging is as a laminate with waxed paper, polyethylene or polypropylene. The barrier performance is then very spectacular compared with most other wrappers. Aluminium foil does not heat seal unless coated with a thermoplastic coating of which wax is the simplest (usually in conjunction with tissue paper) but polyethylene, polypropylene, PVdC or a lacquer are the most usual.

Pressure sealing

Developments in very high speed wrapping, for example, of small bars in flowpacks, has meant that the dwell time in the jaws of the packaging machine has fallen so low that normal heat sealing has become almost impossible. For these applications pressure sealable systems have become useful. The film is coated with a pressure sensitive adhesive and the jaws of the wrapping machine apply the pressure to effect the seal. It will be appreciated that no heat control is then needed and the speed of the wrapping is not critical. In fact in many cases the speed of the wrapping machine is varied to suit the length of the queue of product approaching the wrapper which is a technique that cannot be used where the temperature of the sealing jaws is critical. The pressure sensitive adhesive is normally applied only in the appropriate areas and only on one side of the film. Thus lap seals are not possible and the technique is more or less restricted to flow pack or vertical form-fill-seal wrapping machines.

Materials used within packs for added protection

The majority of biscuits are packed directly within moistureproof films of the types described above. Sometimes a layer of printed paper, plastic skillets, formed pieces of corrugated paper or chipboard cartons, etc. are used to hold the biscuits within the overwrap. Fat migrates from biscuits onto any materials in contact and in the case of many papers, and all uncoated boards, the fat moves though the fibres forming visible grease spots. The extensive surface area so produced combined with traces of metals in the paper encourages rancidity and hence a bad smell together with product deterioration in the pack. Moistureproof cellulose and plastic films do not absorb grease so grease spots do not form.

Greaseproof paper and glassine are paper films which have been heavily calendered (rolled at great pressure) and polished to reduce the tendency for the fat to be absorbed. Most greaseproof papers are expensive, hard and brittle and difficult to print well.

Corrugated paper for use in contact with biscuits is usually made up with greaseproof paper to form the corrugations which touch the biscuits glued to a cheap sulphite kraft paper. Loose biscuit crumb in the pack may result in some fat staining of the sulphite paper.

Cartons of chipboard in contact with biscuits should be lined with glassine or made from coated board to prevent grease staining.

It is important to check that any printing ink solvents or adhesives used on wrappers included within the moistureproof wrap are devoid of odours which could taint the biscuits.

In most cases rigid plastic trays have replaced cardboard cartons within packs to overcome the greaseproof and hygiene problems. These trays are moulded by a process of vacuum forming when heated from reels or sheets of plastic of appropriate thickness.

Overwraps and cases for transportation and storage

Cartons

It is sometimes decided to place the basic film wrapped biscuit pack within a paper board carton. This may be for display, to form multipacks or to give added mechanical protection. Although this is another packaging operation and adds to the cost, it does give a tidy package and, being outside the moistureproof wrapper, the carton can be made of non-greaseproof materials, include waste paper pulp in its construction. It can be sealed with strong adhesives without too much concern about odour. The significance of the waste paper pulp is that this is cheaper than new wood pulp but has a hygiene hazard which precludes its use in containers which come into contact with food. Card for cartons should be selected with due regard for the thickness and hence mechanical strength, whiteness of the surface for printing and, of course, cost. It is a very false economy to use a board which is a little too weak as it may give handling problems in a carton erection machine and if stored in slightly unfavourable conditions become quite useless.

Multipacks

Small groups of the basic packs are known as multipacks. These are formed on a second wrapping machine and it is usual to use an overwrap film of low or only modest moistureproofness to save expense. Cellulose or polypropylene offer the best appearance, but it may be satisfactory to use shrinkwrap.

Fiberites

For the purpose of collation, transportation and storage, biscuit packs are usually filled into corrugated brown paper cases known as fiberites. The size and shape of these depends on a number of factors, but normally there are about 24 or 30 packets giving a total case weight of around 6 or 7 kg. The cases are normally constructed from two webs of brown kraft paper separated by a corrugated layer of similar material. The board so produced is very resistant to compression when the flutings are vertical but at 90° the strength is not so good. It is, therefore, important to consider the construction of these cases and never to stack them lying on their sides. This is a very common error seen in biscuit factories or during transport.

As with other papers, fiberites lose much of their strength if allowed to become damp.

At extra cost, but for improved display purposes, fiberite cases may be made from white faced board. This prints and therefore displays much better than the brown paper.

Shrinkwraps

Shrinkwrapping involves the use of plastic films which are strongly orientated in construction so that they shrink in the longitudinal direction when the plastic is warmed. The biscuit package or case is firstly wrapped relatively loosely in the shrinkwrap film. It is then passed through a short tunnel where warm air is blown onto it. The film shrinks and on cooling a very rigid package is formed. Several different plastics may be used for shrink wrapping films, but polyethylene is the cheapest. This does not have good clarity but is sufficiently transparent and strong for most applications. When selecting shrinkwrap film the specification for shrinkage both in terms of temperatures and amounts in each direction should be considered against requirements.

Tins

In the early days of biscuit manufacturing tins were the main form of packaging and there was much ingenuity in the design of these tins for interest and competitive advertising. Tins offer exceptionally good protection against moisture, light and physical damage. However tins are now used only for very specific types of packaging for biscuits. This is because they are expensive, they take up a lot of space when empty and they are not suitable for high speed filling operations. Where tins are used they are mostly filled manually though there are robotic systems that take biscuits straight from a cooling conveyor and place them into paper cups and into the tins (for example some types of Danish Butter Cookies). It is usual to line tins with paper or to place biscuits in paper within a tin. This is because a biscuit that rubs against the tin surface may develop blackened spots. Clearly the paper must be of a greaseproof quality.

After filling, lids are pressed onto the tin and the lids are normally secured with adhesive tape all round. Thus tins are used principally for high value products and sale as presentation gifts.

Commonly biscuits in tins are an assortment for added attraction. Assembling assortments of biscuits is usually a manual operation and as most tins are filled manually the assembly of assortments is often combined.

Tins are also used for the packaging of biscuits that have to be stored for very long periods. In these cases the tins are sealed hermetically with solder. Plastic boxes that closely resemble tins are also used for special biscuit packs.