Add all ingredients except lime zest to a large Dutch oven or other cooking pot.
Rub butter along the inside pot lip. This will reduce the chance of the mixture boiling over!
Slowly bring the mixture to a boil over medium heat, stirring until the sugar is dissolved.
Turn the heat up a little and cook rapidly, stirring often to prevent sticking, until the jam reaches the gelling point.
Use the plate method to check for gelling or use a digital thermometer. Gelling is reached at 220 degrees or 8 degrees above the boiling point of water.
Add lime zest to the bubbling jam, and stir to distribute throughout the mixture.
Spoon the hot jam into prepared jars, leaving ¼ inch headspace.
Wipe the lip of each jar with a damp paper towel. Top the jars with a lid and lid ring.
Process the jars in a water bath canner for 15 minutes. Remove and let cool completely.
Makes about 6 (1/2 pint) jars.