Glass

The glass container (bottle or jar) is one of the oldest food packages. It is an excellent barrier for protecting food from oxygen and moisture. It can provide food with excellent visibility and an image of cleanliness. Physically, glass is a very high viscosity supercooled liquid. The major constituents of container glass are silica (Si02), soda (Na20), and calcia (CaO), along with small amounts of other inorganic oxides. The properties of glass (such as strength, transparency, and moldability) can be modified by minor changes in the composition of these constituents.

Some important considerations in designing the glass container are mechanical, thermal, and optical properties. Mechanical properties include vertical load strength, internal pressure strength, impact strength, scratch resis-

Table 1 Advantages and Disadvantages of Food-Packaging Materials

Advantages Disadvantages

Glass

Excellent barrier against Easily breakable oxygen and moisture Relatively heavier

Chemically inert Transparent

Metal

Excellent barrier against oxygen, moisture, and light Good mechanical strength and durability Good thermal stability

Relatively inexpensive Excellent printability Lightweight

Most versatile packaging material Can be formed easily into many shapes Lightweight

Susceptible to corrosion Metal cans are generally more difficult to open and reseal

Dor gas and moisture barrier reatly reduced mechanical strength when wet

More susceptible to migration and flavor-scalping problems

Paper

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