The consumer price index is based on a bundle of goods and services purchased by consumers in the U.S. and is a measure of the changing cost of such items. http://www.bls.gov/cpi/ Dr. Elizabeth Hoyt was instrumental in the foundational work leading to the creation of this index and I had the pleasure of being officed near her at Iowa State University during the final year of so of her life and career when I arrived there in the late 1970's. She was in her upper 80's at the time of her death but still came into her office frequently.
According to the most recent release of the index for January 2008, energy costs are on track to rise over 40% (based on an annualized average of the last three months) and food costs are rising at an average rate of about 4.3%. Of course averages betray the distribution beneath.
In the United States, we have a lot of value added in the final food items which reach the grocery store. This often results in a relative small share of the total retail cost of an item being the underlying agricultural commodity cost. The USDA estimates that in 2002, the "marketing bill" had increased to about 81% of total retail food expenditures, leaving 19% as farm level cost. http://www.ers.usda.gov/amberwaves/february04/indicators/behinddata.htm However, some items have far less value added as a share of the final cost.
Eggs for instance are up 40% from last year and milk up 26% since the level of processing is fairly minimal from farm gate to kitchen plate. The gross value of pork at the farm is estimated to be about 26% of the final retail price. This suggests that if pork costs rise 20% because of ethanol feed impacts and all of that is passed through (which probably will not happen but is possible depending on the various elasticities of the markets involved) the retail price of pork would also rise between 5 and 20%, the extreme value of 20% would occur if the farm level cost of pork maintained the same 26% share of the final retail price, which seems unlikely.
All of that is a bit simplified too since the relative price of poultry and beef for instance will also change and there will be some switching between the meats by consumers who are equal opportunity carnivores. Supermarkets and other purveyors will "absorb" some costs at least initially but probably won't allow their margins to be permanently eroded where they can avoid it.
Pork has not begun to rise in cost to the consumer because of the huge glut of supply, decided from last year's breeding decisions, that is working its way through the market place. There will be some liquidation pressure on price soon too that will prolong the pass through of higher costs to the consumer temporarily.
Of all the nations on earth, apparently we have the lowest own-price elasticity of demand for meat if I am to believe the USDA figures on these things, and I do. So in the face of the extreme estimate of a 20% increase in the retail cost of pork, all things being equal (which of course they never are), we can expect purchases to decline a little under 2%.
After examining your own-price and cross-price elasticities for the various meats you consume I would recommend that you get ready to save some money by cutting up those chickens instead of buying the higher priced parts (like the ladies in this article in the Boston Globe http://www.boston.com/business/personalfinance/articles/2008/03/09/surging_costs_of_groceries_hit_home/?p1=Well_MostPop_Emailed1). There is a nice diagram to help you out at http://www.cookingforengineers.com/article/97/Cutting-Up-Chicken
