Mason jars, also known as canning jars, have been used for home food preservation for decades dating back to 1858 when John Landis Mason created and patented a glass jar for home canning. Over the years, various manufacturers have added new designs or color to the standard jar. The unique jars have given consumers the opportunity to use jars in creative ways, for storage and in home décor. However, this has caused confusion when it comes to determining which jars are safe for food preservation.
Colored Jars
The Ball Brothers originally made canning jars in amber or aqua giving way to clear glass to expedite mass production. Over the years, notably Ball®, has reintroduced those colors and others to their line of products giving consumers a variety of colored jars to choose from – blue, green, purple, rose, aqua, and amber. The colors are derived from various minerals added to the glassmaking process to permanently color the glass. All are safe for home food preservation; however, the colored glass does distort the appearance of the food in the jar.
While pretty to look at, colored glass jars also add some additional protection to the food inside by preventing light from passing through to the contents. Clear glass permits all types of light to pass through whereas blue glass reflects blue light, red glass reflects red light, and so on. While they block one color of light, they let other light in. Amber glass, however, provides additional protection to preserved or stored food by blocking UV rays, allowing contents to be shelf stable for a longer time. UV rays have the potential to change contents in glass by photo-oxidation. Amber also offers superior blue light protection which affects food color. By blocking harmful food-damaging UV rays and light, amber makes it possible to store foods in lighter areas or even the counter top without loss of flavor, color, or nutrients. Foods such as baking ingredients, oils, herbs, spices, coffee, tea, or any food item that loses quality due to UV rays can be safely stored in amber jars. And given the natural qualities of glass, no harmful chemicals leach into the products stored in the jars as can be the case with plastic containers.
Other manufacturers have also given consumers colored glass. The difference may be that the color is stained or glazed onto a clear-glass jar. These jars are great for crafting, but are not suitable for canning. Look for a warning label on the packaging or jar: “not for canning”. Further, jars colored by staining or glazing may not be safe for food storage due to the coloring process used. They also may offer no UV or light protection. If a jar is not labeled for canning, food preservation, or food use, avoid using it.
Size and Style
Standard canning jars are available as regular-mouthed (2.75 inches) or wide-mouthed (3.38 inches) and in 4-, 8-, 16-, 32-, and 64-oz sizes. Tested recipes generally recommend the use of 4- and 8-oz jars for fruit spreads. Sixteen- and 32-oz jars are the recommended sizes for many canned foods. Sixty-four-oz or half-gallon jars are only recommended for highly-acidic juices, such as apple and grape, processed in a hot water canner. There are no other recommendations for half-gallon jars as testing has shown that there is inadequate heat penetration to the center of the jars. One-gallon jars are not recommended for food preservation at all.
Manufacturers have offered various styles of the standard sizes. Style is a personal preference. As with colored glass, the jar should be labeled safe for canning. When used with proper canning lids and bands, most of the stylized jars are safe for canning in hot water bath or pressure canners. Per Penn State Extension, tulip-shaped jars are not recommended because the wider part of the jar will not heat at the same rate as the more narrow part.
For additional information on canning jars, visit Canning Jars and Lids–An Update.
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