1. Combine the chopped rhubarb, sugar, and lemon zest in a large bowl. Stir until the sugar coats the rhubarb evenly. Cover with plastic wrap and let macerate at room temperature for 8 to 12 hours, or refrigerate overnight. The mixture will release a rosy pink syrup.

2. Pour the macerated rhubarb and all its syrup into a heavy-bottomed saucepan or Dutch oven. Add the lemon juice and stir to combine.

3. Bring the mixture to a boil over medium-high heat, stirring frequently. The jam will foam up in the first few minutes. Reduce the heat slightly if needed to prevent overflow, and keep stirring.

4. Continue boiling for 15 to 20 minutes, stirring every minute or two. The color will deepen to a rich coral or ruby and the liquid will begin to thicken visibly.

5. Start testing for the gel point at 20 minutes. Use a candy thermometer and look for 220 degrees F, or spoon a small amount onto a chilled plate, wait 30 seconds, and push it with your fingertip. If it wrinkles and holds, it is ready. If it spreads, cook for 5 more minutes and test again.

6. While the jam cooks, wash your jars and lids in hot soapy water. For shelf-stable canning, sterilize jars by simmering them in boiling water for 10 minutes.

7. Remove the pot from the heat. Let the jam sit for 2 minutes, then ladle it into the prepared jars using a wide-mouth funnel, leaving 1/4 inch of headspace at the top.

8. Wipe the jar rims clean with a damp cloth, place the lids on top, and screw the bands on fingertip-tight.

9. For refrigerator storage, let the jars cool to room temperature and then refrigerate. For shelf-stable canning, process the filled jars in a boiling-water bath for 10 minutes, then lift them out and let them cool undisturbed on a towel for 12 hours. Listen for the pop of each lid sealing as they cool.