Prepare two, clean and dry glass quart jars.
In a large bowl, combine the sprouts with the celery seeds, peppercorns, garlic, sea salt, and red pepper flakes. With clean hands, work the salt and spices to blend thoroughly.
Allow the mixture to sit and sweat for 30-45 minutes. The mixture should release its own natural liquid.
Pack the mixture between two quart class jars, compress the mixture as you continue to add to the jars..
Add a tiny bit of additional water to each jar, enough to cover the kraut. Top with fermentation weight or push a jelly jar in the mouth of each jar to allow the mixture to remain submerged in the brine.
Cap loosely or use an airlock. Store on the counter at room temperature, out of direct sunlight, for at least 3 days or as long as 10 days.
Transfer to the refrigerator and allow the relish to ferment for an additional week before eating.