Every jar or bottle you are storing food in needs to be sterilised first, even if it is brand new. Any receptacle that has a tight lid will preserve the food inside it, protecting it from bacteria outside the jar — but if it has not been properly sterilised, you could be trapping harmful bacteria within. Bacteria will rapidly reduce the shelf life of your food, and can also cause serious illness, so it’s very important to sterilise your jars.
Thankfully, sterilising jars and bottles is not that hard at all! One of the most important things to remember is to make sure the jar or bottle, and the food you are putting in it, are the same temperature, to avoid any glassware breakages. Hot food into hot jars, and cold food into cold jars.