Makes about four 1-pint jars
The Ball Complete Book of Home Preserving
In a large stainless steel saucepan, combine rhubarb, brown sugar, raisins, onion, vinegar, allspice, cinnamon, ginger and salt. Bring to a boil over high heat, stirring frequently.
Reduce heat and boil gently, stirring frequently, until mixture is thickened to the consistency of a thin commercial barbecue sauce, about 30 minutes. If you want it thinner you can use an immersion blender to break up more of the ingredients.
Ladle hot sauce into hot jars, leaving 1/2-inch headspace. Remove air bubbles and adjust headspace, if necessary, by adding hot sauce. Wipe rim. Center lid on jar. Screw band down until resistance is met, then increase to fingertip-tight.
Place jars in water bath canner, ensuring they are completely covered with water. Bring to a boil and process for 15 minutes. Remove canner lid. Wait 5, minutes, then remove jars, cool and store.