Hmmm... that's consistent with population growth.
So why has price skyrocketed?
Price of food is directly linked to the price of oil. If oil goes up by a factor of 4, food usually does too. Oil is used to produce the deisel to run the irrigation and tractors. Oil is used to make the fertilizer. Oil is used to harvest and dry and process the food. Oil is used to transport the food. Plus, food and oil are tied together in commodity indices so if investors want one, they often buy the other.
Food is expensive now since oil is expensive now.
Also remember, only the US does large scale ethanol prodcution from corn. So the rest of the world's corn supply grew much faster than population growth. Another massive demand though is the increased use of meat. Eatting one more pound of meat around the world means we have to produce many, many more pounds of grain. The rest of the world is not only eating more calories (more food) but also more meat (more grain per calorie).