Gather and clean all equipment, including pot, thermometer, strainer, jars, and towels before starting.

Pour the maple sap through cheesecloth or a fine-mesh strainer into the large stainless steel pot to remove debris.

If using concentrated maple juice, add 1/4 cup water to the pot and stir to combine.

Place the pot over medium-high heat and bring the mixture to a gentle boil, about 5 minutes.

Insert a candy thermometer and maintain a steady boil, stirring occasionally and skimming foam with a slotted spoon, until the syrup reaches 219°F, about 45 to 60 minutes.

Remove the pot from heat once the thermometer reads 219°F to ensure the proper syrup consistency.

Immediately pour the hot syrup into clean glass jars, leaving a little headspace, and let cool at room temperature for about 30 minutes.

Seal the jars and store the syrup in the refrigerator for up to 2 years or freeze for extended storage.