Food prices are not perfectly elastic when it comes to the basic staples like wheat, especially in the short term. People need a certain amount of food, and their choices come down to eat if you can afford it, or die. Demand by households doesn't change much with price, but they will pay anything from zero up to everything they have.

The price is therefore depends on the suppliers. Normally, competition between suppliers will bring the price down to near the cost of production. However, if there is a futures market filled with overly confident speculators, who buy the grains at a high price and push it even higher, the cost to all the owners of the stock when delivery is due will be far higher than the cost of production; if most of the market paid this same price, there will be no-one with the volume who can afford to compete and push down prices; the final price is likely to strike a balance between the loss of value from throwing away wheat because some people had to starve as they couldn't afford the price, and the revenue from selling the wheat at the highest price.

In effect, against inelastic demand, a futures market and confident speculators have the same effect as rational price fixing by a cartel.