Sterilizing glass jars is extremely important if you want to preserve jams, marmalades, jellies or chutneys. It is unhealthy and risky for you to do otherwise.
Preheat your oven to 100 degrees Celsius.
Wash the glass jars and their lids with soap in hot water. Place them, while still damp and without touching the inside of the jars and lids, on a baking tray lined with a clean tea towel. Make sure you place them open sides up. Put the tray in the oven for 35 minutes.
Take tray out of the oven and carefully pour your hot jam, jelly, marmalade or chutney inside the hot jar. Be careful not to touch the inside of the jar. Close the lids tightly (not too tightly).
At this point, you can turn the jars upside-down and leave them to cool completely. You can keep them in the refrigerator for up to 3 months.
If you want to preserve the jam/chutney/marmalade for longer outside the fridge, then fill a large, heavy-bottomed pan with water and once it comes to the boil, fully submerge the glass jars in it, placing them in the pan upright, with the lid side up. Leave them in the boiling water for 10 minutes and then, using tongs, carefully remove them from the pan. Allow the glass jars to cool completely. Check to see if the lids have sealed. If a lid of a jar hasn't sealed properly, put the jar in the refrigerator and use it first.
Store the filled jars in a cool, dark and dry place. Once you open them, place them in the refrigerator.
After this process the jam/chutney/marmalade/jelly can be kept for up to a year unopened.
Important: Don't recycle mayonnaise, jam, mustard or any other jars for your canned goods. Buy new canning jars and once you have used the lids once, buy new lids. Never use the same lids twice.
It is also important to inspect the glass jars for scratches, chips or cracks. They must be in pristine condition.
You will find this helpful in the following recipes:
Cherry Tomato Jam
Homemade Fig Jam