This jam can be made in early spring, when you want new flavors, bright and rich.
Remove tough outer fibers from the rhubarb, cut crosswise into small pieces 1.5-2 cm thick, pour over with vinegar and mix. Sprinkle with sugar and leave for 1 hour.
Wash the oranges thoroughly with a brush. Dry and remove the zest with a special knife (or thinly cut and cut into strips). Squeeze juice from oranges.
Add the orange zest and juice to the sugared rhubarb and stir to combine. Place over medium heat, bring to a boil. Reduce heat to low and cook, stirring gently, until thickened, about 25 minutes.
Arrange in sterilized jars, close and roll up if desired.