Natural Strawberry Rhubarb Jam

Combine rhubarb and sugar in a large, sturdy container and allow it to sit for 2 hours; stir in lemon juice and strawberries. Introduce the mixture to a boil, stirring until the sugar dissolves completely. Set the heat to medium-high and cook the jam at a rolling boil until it reaches the desired consistency, stirring frequently to prevent scorching, approximately 20-25 minutes. A candy thermometer inserted into the middle of the jam should read 220 degrees F (105 degrees C).

Take the jam off the heat and stir for an additional 2-3 minutes; remove any foam that forms on the surface.

Sterilize the jars and lids in boiling water for at least 5 minutes. Fill the sterilized jars with the jam, leaving a small gap of about 1/4 inch between the top of the jar and the lid. Use a knife or thin spatula to remove any air bubbles that may have formed during filling. Wipe the rims of the jars with a damp cloth to remove any food residue. Secure the lids and screw on the rings.

Position a rack in the bottom of a large stockpot and fill it halfway with water. Bring the water to a boil over high heat, then carefully lower the jars into the pot using a jar holder. Leave about 2 inches of space between each jar. Add more boiling water if necessary to ensure the water level is at least 1 inch above the tops of the jars. Bring the water to a full boil, cover the pot, and process for 10 minutes.

Remove the jars from the stockpot and place them on a cloth-covered or wooden surface, several inches apart, until they cool. Allow the jars to stand on wire racks for 24 hours to cool and seal completely. Once cooled, press the top of each lid with your finger, ensuring that the seal is tight (the lid should not move up or down at all).