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Just as there are many different ways of preserving foods, there many different types of preserving jars as well. Basic glass Mason jars are the staple supplies of most home canners, but they are by no means the only option. Decorative and shaped jars are also popular. So long as a jar has a reliable, airtight seal, it can likely be used for some type of preserving.
Most preserving jars are made of glass, though some are also composed of plastic or various metal composites. Much of this usually has to do with how the food is being preserved. Preserving foods through home canning, open kettle canning, and bottling usually requires glass because of the high temperatures involved. Frozen preservation is more flexible, and nearly any jar can be used for this purpose.
An airtight seal is one unifying feature of all preserving jars. One of the main goals of preserving is to store food safely for later consumption. Often, jarred food is kept for months, if not years. It is able to stay fresh throughout all this time because the preserving process removes the air and kills any latent bacteria.
Food preservation has been going on for centuries, well before the advent of modern canning technologies. Early preserving jars come in a wide variety of shapes, sizes, and colors, but are almost always made of glass. Many of these jars were sealed with corks, fitted stoppers, or even wax seals.
Today, the most common jar seals are metal discs that sit atop a jar’s opening and are held secure with a matching metal ring. Some cooks prefer to use plastic seals, which are less sturdy but are often re-useable. Metal seals can typically only be used once.
Preserving jars used for storing fruits and vegetables are typically rounded glass jars with wide mouths, capable of holding whole fruits or fruit slices. Jam and jelly jars are usually a similar shape, but are often smaller and may feature decorative glass work or other adornments. Bottled foods, including ketchup and sauces, are usually stored in narrow-necked jars with much smaller lids.
Jars in all categories come in a variety of shapes and sizes. Many people preserve foods, particularly jams and sauces, that they intend to give away as gifts or sell at farmer’s markets or local shops. Appearance is usually important for gifts and sales, and many of these preserving jars are shaped, fluted, colored, or textured. The added expense of these design elements does not always make sense for simply canning at home.