Low sodium teriyaki sauce

Name: Low sodium teriyaki sauce
Prep time: 5 min
Cook time: 30 min
Total time: 35 min
Cuisine: Asian
Ingredients: 2 cups (500ml) water; 3 squares kelp; 1/2 medium apple, peeled (about 95g); 1/4 medium yellow onion (about 105g); 6 cloves garlic; 1 inch fresh ginger; 3 tablespoons coconut aminos; 1 tablespoon rice vinegar; 1 tablespoon cornstarch; 2 tablespoons cold water