As at the Federal level, the Ohio Constitution provides the ultimate boundaries of what can and cannot be taxed in Ohio. Also see the Constitution tab of the Ohio Primary Law Research Guide. Article XII of the Ohio Constitution is entitled Finance and Taxation and consists of 13 sections. Section .03 of Article XII prohibits the taxation of food.
The Ohio Supreme Court is "taxed" with construing the Ohio Constitution. Here are a few recent decisions of that Court which analyzed the tax sections of the Ohio Constitution.