It is common to buy food for many days at once as one cannot go to the market every day. But the problem is you cannot leave food items as it is in the kitchen. Many of the food items are properly packed when bought form the grocery store and have an expiry date also. But in case of fresh unprocessed items, their expiry period is very short. If not properly taken care of they will rot soon. Refrigerators are a very good option to store food but before their invention, the common method of preserving food for long time was canning. This technique has not lost its popularity due to invention of refrigerator and is still very useful. Even in a refrigerator, food can easily be placed if properly canned to save the space.
Canning involves use of jars and usually by jars people mean glass jars. Canning jars have been in use since 1850. The design of glass jars was then worked on by John L. Mason to improve their efficiency and as a result of this improvement, mason jars were formed. What actually he added to the old glass jars was a metal screw-on lid to preserve the food more effectively. Now the jars manufactured have same basic design but come in different sizes. Most common of them are Half-gallon, quart, pint and half-pint mason jars.
There are three parts of a mason jar. First is the obvious one that is glass jar itself. There are two types of glass jars also, wide and regular mouthed. Normally these glass jars are totally clear but some companies also make colored jars. A very attractive color is aqua but other colors can also be found. The second part is the metal screw-on ring for which John Mason got patents specially. But this screw is not of much importance in canning the food.
Many people also store their food without this ring. It has nothing to do directly with sealing the jar. It only supports the center portion and prevents it from getting knocked off. Also, it can keep the contents inside the jar from spreading all over the place in case the seal breaks.