Separate the leafy parts from the Swiss chard stems, and keep the leaves aside for another dish.
Chop the Swiss chard stems, along with the celery, onions, and red pepper, into small pieces. However you chop the pieces will determine the consistency of your relish (I like about½-inch).
start the relish
Place chopped vegetables in a large bowl and add salt. Mix well and allow to sit for one hour. The salt will draw some of the liquid out and pre-ferment the vegetables. Rinse the vegetables in cold water and drain.
Add vegetables, along with the vinegar and water, to a large pot, and bring to a boil over high heat. Reduce heat to low and simmer for 10 minutes.
make the sauce and finish
Meanwhile, in a mixing bowl, combine all the ingredients for the sauce.
Use a ladle to remove about 2 cups of cooking liquid from the vegetables and mix it together with the sauce ingredients.
Add the sauce to the pot with the vegetables, stirring continuously. Simmer 2-3 minutes, until the mixture thickens.
Let cool to room temperature, then refrigerate. If you would like to preserve your jars for the winter, see the recipe notes!
Notes
Method for canning
We will use the water bath canning method for 15 minutes. You will need a pot large enough to hold your canning jars, and a trivet or steamer insert to keep the jars off the bottom of the pot to avoid breaking jars. You will also need a jar lifter and a funnel to fill the jars. Your jars will also need fresh sealing lids and rings.
Fill the pot with water and place empty jars in the water. Bring to a boil and boil for 5-10 minutes. Alternately, run your jars through a sterilizing cycle in the dishwasher.
Transfer hot Swiss chard stem relish into jars using the funnel. Leave at least ¼ inch space at the top of the jars. Use a clean cloth to wipe the top edges of the jars clean. Cover with sterilized lids, then add the rings and tighten until finger tight.
Use a jar lifter to transfer the prepared jars into the water bath. Set a timer for 15 minutes after the water begins to boil. Remove using the jar lifter and allow to cool for 24 hours, or overnight.
Remove the rings and check the seals. Wash jars using soap and water, then dry. Label with the contents and date. Store in a cool, dry place.