Making jam requires combining fruit, sugar and water over heat until it solidifies and settles into the texture of a jam. Additionally, adding fruit pectin causes the jam to be more gelatinous out of the jar, regardless of temperature. Jams made without fruit pectin need to spend time in the fridge before use to acquire the right texture.
The amount of sugar required changes depending on the ripeness of the fruit, as fruits lose sweetness as they age, requiring more sugar to preserve the jam's flavor. However, a general rule is to use 2 cups of white sugar for every 1 pound of fruit.
Start by combining the fruit and water in a pot and bringing it to a boil. Then, reduce to medium heat, cover the pot, and allow the fruit and water to simmer for about 5 minutes. Next, stir in the sugar, and increase the heat, bringing the mixture to a rolling boil, all the while stirring constantly. If adding pectin, do so now. Boil the jam for about another minute, continuing to stir it. Remove the pot from heat, skim off any foam and set the pot aside.
To store the jam, start by boiling jars in water for at least 5 minutes to sterilize them. Fill the jars with jam, leaving about 1/8 inch of space on top. Seal the jars and fully submerge them in boiling water for 10 minutes to vacuum seal them. You can now store the jam without refrigeration.