Sterilize the jars. I place the jars and lids on an oven tray and leave them in the oven at 150C (302F) for 15 minutes.
Meanwhile, rinse the rose flowers to remove any bugs or impurities.
Take the petals off and put them in a bowl.
In a large, non-stick pot, add the lemon juice, water and sugar. Place the pot on high heat and mix well.
Once it starts bubbling and all the sugar is melted (6-10 minutes), add the rose petals.
Mix well to coat all the petals in the syrup.
Place a kitchen thermometer in the jam while stirring continuously. Once it reaches 105C (221F), you can turn off the heat.
Let the jam cool a bit.
Using a ladle, pour the jam into each sterilized jar. With a wet, clean cloth, wipe the jars of any spilled jam, especially near the lid area.
Cover with the lids and screw them on tightly.
Leave the jars at room temperature until the next day.
All lids should seal by the next day. Check for the seal, then store in your pantry.
Notes
Yields a small batch from 12 large roses. To scale up, increase petals and sugar proportionally and keep the 105C (221F) setting point regardless of batch size. Store sealed jars in a cool, dark pantry.