In a bowl, add everything except for the wheat gluten (warm water, ketchup, refined coconut oil, smoked paprika, liquid smoke, mustard seeds, garlic powder, onion powder, salt white pepper, black pepper, and celery seed) and stir well.
Mix in 3/4 cup of the vital wheat gluten with a silicon spatula, then knead in the remaining 1/4 cup a little at a time with your hand. (Add the wheat gluten until it no longer easily absorbs into the dough.)
Shape the summer sausage into a log shape and wrap it tightly in foil. (You can wrap it in a layer of parchment before wrapping it in foil if you don't want the foil to touch your food.)
Place the wrapped sausage into a steamer basket and steam for 50 minutes. (or in a pressure cooker or Instant Pot for 40 minutes and allow steam to release naturally.)
Allow the sausage to cool and then slice and serve. (It will firm up even more if allowed to cool completely overnight in the fridge.)
Notes
Small changes in the amount of vital wheat gluten you use will change the texture of the final result. More gluten gives you a firmer texture and less gives you a softer texture.
I find the best texture is achieved if you add vital wheat gluten until the dough doesn't easily absorb more, yet not so much that the dough becomes rubbery and you are not able to form it into a smooth shape.
You can eat the sausage immediately after steaming, but it has the best texture and flavor if allowed to cool completely in the fridge.