Can a snack bar cook porridge without smoke machine?

It depends on your space size and air circulation area. If the space is relatively large and the air circulation is relatively smooth, then it doesn't matter if you don't feel at ease. Of course, if the area is not that big, you'd better install it. After all, you may expand into cooking other foods in the future. Although porridge seems to have no oil smoke, it is not in the right time and space, and the color of indoor smoke is not good.