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Written by Khor Yin Chen (Jane) who study in Universiti Sains Malaysia.
I came from Alor Star, Kedah, a peaceful state where I love it very much. I am a passionate person, who always try to find passion on doing every little stuff, no matter I like it or I don't, as I believed "Everything happened for a reason".

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Unlacqured can bodies

Presence of tin is desirable because it eliminates oxygen

Prevent discolouration of the contents

Through oxidation of the tin surface in preference to oxidative degradation of the food

Fully lacquered cans do not allow this flavour to develop

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The colour of juice plays an important role of lacquering coating of metal can.

Clear Juice

Unlacquered can bodies

covering liquid might juice will become cloudy or discoloured through oxidation if there is lacquer coating

E.g. pears, peaches, pineapples and yellow plums

Color Juice

Full lacquer bodies

Quickly discoloured by contact with tin or iron without the lacquaring coating

E.g. coloured fruits that contain anthocyanin pigments (strawberry, cherries, blackberries)

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Vegetables, meat, soups and fish contains high sulphide compound
where the sulphur staining could be a problem. In order to prevent it, the metal can normally coated with zinc oxide-modified epoxy-phenolic lacquers due to

promotion of meat release properties

preventing the contents from sticking to the sides of the can

prevent sulphur blackening of the tinplate

Function of zinc oxide

the lacquer soften during sterilisation

permits the sulphur compounds to react with the zinc oxide

produces zinc sulphide (white in colour and harmless)

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Different type of food product requires different type of lacquers coating.

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1. Able to withstand the conditions.

2. Resistant to food during processing and any by-products

3. No migration of components of the coating layer

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Soft drink are normally contains high amount of acid, in which corrosion might be happened in metal can and become a potentially serious problem.

The lacquer applied on the inner surface of the metal can is important in order to protect the can and prevent the migration of can material into food due to its high pressure processing.

Below are the application of different type of lacquer coating used in beverage can:
1. Draw and wall ironing cans
(Aluminium)

Water-based epoxy acrylic system

2.Three-piece tinplate (Steel)

Epoxy phenolic basecoat with an epoxy acrylic internal spray

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Since the lacquer will have direct food contact with food, hence only limited number of chemical substances can be use. However, there is many variation of each type.
1. Epoxy phenolic

Universal gold lacquer for three piece can

Has good flexibility

High heat stability

Resistance to acid

Excellent chemical stability especially sulphide ion

2. Organosol

Often used over epoxy phenolic basecoat.

Very good flexibility

Very good pack resistance

3. Phenolic

Very poor flexibility

Excellent pack resistance

Oustanding chemical stability especially sulphide ion

4. Arcylic

Good color retention

High resistance to heat

Provide internal protection as hard white coatings

5. Oleoresinous

Flexibility is depended on the type of resin used

Very limited use

Usually modified with addition of zinc oxide

prevent the blackening of food product due to the presence of sulphide.

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A protective layer is coated on the inner surface of the metal can after heat treatment in order to protect the food, which also known as lacquer.

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The metal can used to pack food is usually made of tin, aluminium and steel. However, some of the food will react with the metal and cause corrosion and production of toxic substances.

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Since 18th century, canning process has been introduced in order to preserve food in France. It is a method of preserving food in which the food contents are processed and sealed in an airtight container. Canning provides a shelf life typically ranging from one to five years, although under specific circumstances it can be much longer.