Place sprouts, mixed herbs, peppercorns and garlic in 1-quart glass Mason jar, leaving about 2 inches headroom. Set aside.
Whisk salt and 2 cups water in a bowl until salt is almost dissolved, making a brine.
Pour 2 cups brine over sprouts; place 4-ounce Mason jar (without lid) on top of the sprouts to keep them submerged. Drape a large kitchen towel over the jar and let sit at room temperature (ideally 70°–75°) until sprouts have cured to taste, about 3–4 weeks.
Once sprout kraut is soured, cover jar with lid and refrigerate for up to 6 months.