Place squash, bell peppers, and onion in a colander. Sprinkle with kosher salt; cover and let stand at room temperature 1 hour. (Do not rinse.) Tightly pack squash mixture in 4 (1-pt.) hot sterilized jars, filling to 1/2 inch from top. Bring sugar, vinegar, mustard seeds, and celery seeds to a boil in a Dutch oven over high heat; boil, stirring constantly, 1 minute or until sugar dissolves. Pour hot liquid over squash mixture in jars, filling to 1/2 inch from top. Remove air bubbles by gently stirring with a long wooden skewer. Seal and process as directed (see below), increasing boiling time in Step 3 of canning instructions to 15 minutes.
A Three-Step Guide to Puttin' Up
Yes, it really is that easy. To get started, you'll need a basic canner, a jar lifter, and a canning rack. Look for a 9- or 12-piece canning kit, which will include all of these pieces and more.
Step 1: Sterilize.
Bring a canner half full of water to a boil; simmer. Place jars in a large stockpot with water to cover; bring to a boil, and simmer 10 minutes. Place bands and lids in a large saucepan. (Always use new lids.) Using a ladle, cover bands and lids with hot water from canner to soften gaskets. Let stand 10 minutes.
Step 2: Prepare Recipe.
Meanwhile, prepare recipe. Remove hot jars from stockpot, 1 at a time, using jar lifter, and fill as directed in recipe.
Step 3: Seal & Process.
Wipe rims of filled jars. Cover at once with metal lids, and screw on bands (snug but not too tight). Place jars in canning rack, and place in simmering water in canner. Add more boiling water as needed to cover jars by 1 to 2 inches. Bring water to a rolling boil; boil 15 minutes, adjusting processing time for altitude.* Turn off heat, and let stand 5 minutes. Remove jars from canner, and let stand at room temperature 24 hours. Test seals of jars by pressing centers of lids. If lids do not pop, jars are properly sealed. Store in a cool, dark place at room temperature up to 1 year. Refrigerate after opening.
*Consult the USDA Complete Guide to Home Canning at nchfp.uga.edu/publications/publications_usda.html to adjust processing times for altitude.