4 cups sliced rhubarb, cut into 1/2 inch slices
2 1/2 cups thinly sliced onion
1 cup raisins
2 cups light brown sugar
2 cups apple cider vinegar
1 tablespoons salt
2 1/2 teaspoons pumpkin spice
1/8 teaspoon cayenne pepper
Combine all ingredients in a heavy non reactive large stainless steel or enamel-lined saucepan.
Bring to a boil and simmer gently for 40-45 minutes with the lid off, stirring frequently. Be sure to keep an eye on it the last 5 minutes and not let it stick to the bottom of the pan.
Pour into sterilized pint jars, leaving about 1/2 inch head space, cover with sterile lids and bands, and process in a hot water bath for 10-15 minutes.
Remove and set on a towel-lined counter top until jars have cooled to room temperature. Remove bands and check seals.
Store in a cool dark place until ready to use. Once opened, store in the refrigerator.