Remove the stems from the portobello mushrooms and discard. Scrape the gills from the underside of the mushroom caps and discard. Slice the caps into ½-inch pieces.
In a small bowl, combine the soy sauce, Worcestershire sauce, maple syrup, smoked paprika, garlic powder, liquid smoke, onion powder, pepper, and cayenne pepper. Transfer this mixture to a Ziploc or reusable silicone bag and add the sliced mushrooms. Place in the fridge for 24 hours to marinate, giving the bag an occasional shake.
Preheat oven to 200 F.
Remove the mushrooms from the bag and place on 2 large baking sheets that have been lined with parchment paper.
Bake for 2 ½ hours, turning halfway, or until the mushrooms have reduced in size, browned, and dried out.