Any cash commodity must fulfill 3 basic requirements before it can be successfully traded in the Futures market:
The commodity has to be standardized and for the industrial & agricultural commodities, it must be in an unprocessed form. There are futures contracts which exist for wheat for instance, but not for flour. Wheat is an agricultural product in its raw unprocessed state. (Note that different kinds of wheat will have different Futures Contracts).
The miller needs a wheat Futures contract to help him hedge his risk from price uncertainties while his customers for flour do not require flour Futures for such a purpose. A fixed quantity of wheat will yield a fixed amount of flour. The processing cost of wheat to flour is also fixed thus everything here is predictable.
Sufficient shelf life is necessary for perishable commodities, because the delivery on a Futures contract is delayed.
The price of the commodity must fluctuate sufficiently to create uncertainty which allows for risk and the likelihood of profit (or loss!).