PACKAGING FOODS IN GLASS
Introduction
This technical brief is intended to advise small-scale producers on the methods and equipment needed to package foods in glass jars and bottles. For a more detailed account of the types of foods that can be packaged in glass, the properties of glass containers, label design and production and the economic implications of introducing glass packaging the reader is advised to consult Appropriate Food Packaging by P J Fellows and B L Axtell, ILO, Published by Practical Action Publishing, 2002
General outline of procedures
Process summary New jars or bottles Inspect Rinse Reused jars or bottles Wash
Inspect Sterilise ~ For hot filling and cold filling Fill ~ Liquid fillers or solids fillers Seal ~ Caps for bottles, lids for jars Process ~ Some products are heat processed Cool Label ~ Glued paper or self-adhesive labels Collate into shipping container ~ Cardboard boxes, shrinkwrap or stretchwrap films
Inspection and preparation of containers
All incoming glass containers must be inspected for cracks, chips and small bubbles in the glass. New jars and bottles should be rinsed in clean water and chlorinated if necessary by adding 2-3 drops of household bleach per litre of water.
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Packaging foods in glass
Practical Action
Second hand bottles must be thoroughly inspected, both by looking for chips etc and also by smelling the containers to make sure that they have not been used for storing kerosene or poisonous chemicals (insecticides etc). All contaminated containers should be removed and not used for foods. Second hand containers should be soaked in a 1% solution of caustic soda with detergent to remove old labels. The interior should be cleaned with a bottle brush (Figure 1) and then rinsed thoroughly. Rinsing is time consuming and can be speeded up using a bottle rinser (Figure 2). Many foods that are packaged in glass are then heat processed and for these it is usual to hot-fill the containers (fill at 80°C or above). Glass has to be heated and cooled carefully to avoid the risk of breakage and therefore it is usual to pre-sterilise containers before hot filling. This can be done by placing bottles/jars in a large pan of warm water and heating it to boiling. The containers are boiled for 10 minutes and then removed for immediate filling and sealing. Figure 1: Bottle brush Alternatively a steamer (Figure 3) can be constructed and bottles/jars steamed for 1-2 minutes. This uses less energy and saves considerable amounts of time compared to using boiling water. However, care is needed to make sure that the containers are not heated too quickly, as they will break. Any weak containers will also break at this stage and bottle sterilisation should therefore be carried out away from the food production area to avoid the risk of contamination by broken glass. Tongs as shown in Figure 3 should be used in all cases when handling hot containers. Figure 2: A bottle rinser For foods that are cold filled and then heat processed it is not necessary to pre-sterilise the container. For cold filled foods that are not subsequently heated it is essential to make sure that the jar or bottle is sterilised by one of these methods to prevent contamination of the product by any micro -organisms on
the glass.
Filling Most foods that are packaged in glass are either liquids, such as drinks and syrups or thicker pastes such as sauces, chutneys etc. There are basically two types of filling equipment: those used for solid foods and others for liquid foods.
Figure 3: A steamer 2
Packaging foods in glass
Practical Action
Solids fillers There are few paste filling machines that are cheap enough for small-scale processors but an example of one type (a piston filler) is shown in Figure 4. Most producers fill by hand and although this is slow it can be speeded up by the use of a simple funnel and rod (Figure 5). In the case of solids such as fruit that is packed in syrup, the solid pieces are first placed in the jar by hand and the liquid is then filled using a liquids filler. Liquids fillers Figure 4: A piston filler The simplest method is to fill containers from a jug that is calibrated for the correct volume. A funnel can be used to assist filling narrow necked bottles. A simple frame to tilt jars so that the correct filling level is achieved is shown in Figure 6, this will also speed up the filling operation. At a larger scale of production, a filler can be made by fixing taps into a 50 litre stainless steel bucket (Figure 7). Food grade plastic is acceptable for cold filling. However, these methods are relatively slow and therefore only suitable for small production rates (eg up to 1000 packs per day). They also give some variation in the filled volume, even with careful training of the operators.
Figure 5: Funnel and rod
At higher production rates a piston filler gives a uniform fill-volume and can be adjusted to fill different containers from 25-800 ml. Typical outputs are 15-30 packs per minute. A different approach is to use a vacuum filler. These are available commercially but can also be made locally. The principle of operation is shown in Figure 8. A venturi pump, obtained from a laboratory supplier, is attached to a water tap to create the vacuum. This then sucks liquid from a product tank into the bottle until it fills to a pre-set level. Figure 6: Simple frame and jar filling
Figure 8: Vacuum filler Figure 7: Bucket with tap
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Packaging foods in glass
Practical Action
Sealing
Most caps for bottles and jars have a ring of plastic material (someti mes waxed card or cork) which forms a tight seal against the glass. During hot filling and heat processing this plastic softens and beds itself around the glass to make an hermetic seal. However, before this happens there is a risk that small amounts of air can be sucked into a container and cause contamination of the product. The risk of contamination can be reduced by laying a filled container on its side for about 10 minutes to ensure that the seal is perfectly formed. Specific types of equipment are used for sealing the different caps that are used for glass containers. For bottles the main types are: crown caps roll-on-pilfer-proof (ROPP) caps snap-on caps corks
For jars the main types are: twist-on-twist-off (TOTO) lids push on lids All lids and caps should neither affect the product nor be affected by it and they should seal the container for its expected shelf life. This is usually found by testing trial containers with the product to be packaged to make sure that there is no interaction betwe en the pack and the product. Expert advice should also be sought from the packaging suppliers when selecting the type of closure to be used. Bottles Crown caps are commonly used for beer bottles and fruit juices. Hand -operated equipment is available in a number of sizes from a simple former that is placed over the cap and hit with a mallet, to the hand-held lever type shown in Figure 9 and table mounted model shown in Figure 10.
Figure 9: Hand held bottle capping
Figure 10: Table mounted bottle capping
Roll-on-pilfer-proof (ROPP) caps are fitted by placing a blank cap on the bottle and then pressing the metal into the screw thread of the glass. Finally, a ring of perforated metal is formed at the base of the cap that shows evidence of tampering or pilfering. Hand operated ROPP machines can be constructed locally (Figure 11) and small motorised version are available commercially (Figure 12). A simpler cap which does not incorporate the pilferproof feature is known as a 'Roll-on (RO) cap and this can be fitted by similar types of equipment.
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Packaging foods in glass
Practical Action
Figure 11: Hand operated ROPP machine
Figure 12: Motorised ROPP machine
Plastic snap-on caps are fitted over the neck of the bottle and sealed by a capping machine (Figure 13). Corks are mostly used to seal wine bottles and hand operated corkers which both squeeze the cork and insert it into the bottle are available (Figure 14). Co rks are first wetted to make them slip more easily into the bottle and they then expand to give an airtight, waterproof seal. As corks may be contaminated by microorganisms, it is important that the soaking water contains either a few drops of bleach per litre or sodium metabisulphite at approximately one teaspoonful per 5 litres.
Figure 13: Capping machine
Jars Push-on lids are still used for sealing jars (Figure 15) although these are increasingly being replaced by twist-on-twist-off (TOTO) lids. Small equipment is available for each of these types of closure.
Figure 14: Hand operated corking machine
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