Food prices at the wholesale level rose last month by the most in 36 years. Cold weather accounted for most of it, forcing stores and restaurants to pay more for green peppers, lettuce and other vegetables, but meat and dairy prices surged, too.

The big questions are how long food prices will keep rising and how high they'll go. The impact is already visible. Wendy's, paying higher prices for tomatoes, now puts them on hamburgers only by request. Starbucks and Dunkin' Donuts have raised prices because they pay more for coffee beans. Supermarkets warn customers that produce may be of lower quality, or limited.

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At the same time, global prices for corn, wheat, soybeans, coffee and other commodities have risen sharply in the past year. That's raised the price of animal feed, which has pushed up the cost of eggs, ground beef and milk.