In general, "Mason jar" is a catchall term for glass jars with metal screwtight lids used to preserve homemade foods such as jam, chutney, and salsa. The hermetically sealed jars became popular in the 19th century as the latest technology to keep fresh food from spoiling over the winter. Now, home canning has brought them back as gardeners and chefs want to produce their own sauces.
Mason jars refer to any home canning vessels with three parts: a glass jar with a grooved lip, a flat metal lid, and a screw-on metal ring that presses the lid to the jar. First, the jar is disinfected with a thorough boiling. Then, the food contents are heated, poured into the jar, and covered by the two-piece lid. When the food and air cools, the pressure inside the jar decreases and "pulls" the flat lid firmly shut. Even though the process involves glass, home preserving is referred to as "canning." Collectors of Americana value the older, tinted jars as rare antiques.
In the years before science understood the methods of spoilage, safe preservation was limited to dried, pickled, smoked, or salted foods. Over the winter months, Americans living on the frontier had a limited diet, as their fruits or vegetables wouldn't last through the season. In 1810, Francois Appert put fruit in glass jars, heated them, and sealed them with wax. He believed that the lack of air, rather than heating, was responsible for keeping the fruit from rotting. Others tried sealing jars with cork, wax, leather, and paper, to take advantage of this new, misunderstood technology.
It wasn't until John Landis Mason patented his version of an easy-to-use glass jar with a threaded lip and metal cap in 1858 that the reliable technology entered every pioneer household. People could preserve their summer and autumn harvests for winter at minimal expense. The glass jars, embossed with "Mason's Patent Nov. 30th 1858," were even reusable from year to year.
The impact of canning on people's diets and budgets cannot be overemphasized. Neighbors could even trade, say, their prized apple preserves for another's blueberry jam. In 1861, when Louis Pasteur explained that boiling the jars and food killed microscopic organisms, it became clear why the process worked. Canning in Mason jars provided a major source of food from the Civil War through World War II, until food shortages made it ineffective.