Cut your pineapple. To cut pineapple without wasting too much of the skin. Cut out the center too because the pineapple center is too hard. You can eat the pineapple center, there is nothing wrong with it (some people get an itching in the throat).
Place the pineapple pieces into a pot and add in the sugar. Mix the content. Let it sit for a little while so that the juices can mingle.
Place the pot on the heat and bring slowly to a rolling boil. Then bring down the heat to a low flame and let the jam simmer slowly.
Check with your thermometer if the jam is ready or do the running jam test with a cold spoon or plate.
If the jam is set, get your clean immersion blender and just blend the jam real quick into a smooth consistency. Keep on the heat for a few more minutes after that just to make sure to kill all germs.
Then grab your sterilized jar and lid and fill up your jar with the jam up to the rim. up to the rim is a must!)
Close the jar with the lid very well and quickly turn the jar upside down to create a vacuum. That way your jam will preserve very well for a long period of time.
Keep your jar upside down overnight and then store your jam in a cool, dark and dry place (not in the hot attic or wet cellar!). That way you can store your jars for more than 8 months. Once you open the jars store in the fridge.
Video
Notes
Use pineapple without the center and the skin
Sterilize your glass jar and lids by placing them into the oven or boiling them. Sterilizing means the germs are all killed. Then touch only the glass jar with proper jamming tongue and kit.
Turning your jam jars once sealed upside down creates a vacuum. That's an old French trick.