Ball Mason Jars are canning jars, intended for home canning of food. To do that, the traditional method was to heat the jar and allowing it to cool. Due to steam escaping from the jar, a vacuum is created when it cools down and this keeps the lid tightly sealed over the jar. The removal of air and thus oxygen in the jar prevents mold and some bacteria (which causes food to spoil) to live, allowing the food to last longer.
There is now an easier way to remove air from the jar. The FoodSaver Wide-Mouth Jar Sealer is an attachment that fits on top of the Mason Jars. It is a simple device that allows you to suck air out of the jar, and you don’t actually have to use the FoodSaver System (quite costly) to do that. I learned this from Salad in a Jar. You just need to get the Ziploc Vacuum Starter Kit.
I use the jars to store salad (keeps it fresh for a week instead of lasting just 2 days), honey lemon preserve (vacuum optional), sliced ham, evaporated filled milk, sauces, coffee beans and so on. They are almost infinitely reusable and will save you a lot of money in the long run.
I cannot understand why retailers don’t bring in Mason Jars to sell at mass market prices. A quick check on the internet shows that online sellers generally sell each Mason Jar at S$8! That is A LOT more expensive than the price on Amazon (US$17.90 for 12 jars which is only about S$2 per jar). Unfortunately Amazon no longer offers the free shipping to Singapore on this item. Thank goodness i managed to get the free shipping, but the 12 jars i have are barely enough to go around now. You still do get free shipping with the Jar Sealer and Ziplock Vacuum Starter Kit. By the way, the Mason Jars come in regular and wide-mouth versions. Get the wide-mouth version, which obviously has a wider mouth that makes filling or removing food from the jar easier.
Update 25/3/2016: i recommend getting this suction pump from Taobao instead of the Ziploc Vacuum Starter Kit.
Here are the links for your convenience:
Wide-Mouth Mason Jars