A New York Times opinion piece invited four prominent economists to explain why they believe food prices are rising. The paper had reported that food prices spiked in April, even as oil and gas prices were down.

One of the experts, UC Davis Cooperative Extension agricultural economist Roberta Cook, made the point that food prices are rising because consumers have signaled they are willing to pay more to get what they want.

For example, consider the tomato. "A tomato is no longer a tomato is no longer a tomato," Cook wrote. "American consumers complained for years that tomatoes no longer tasted like tomatoes. The market responded to give them more of what they want."

Getting what they want increased prices.

Cook wrote that specialty tomatoes cost more to produce and harvest; they have a shorter shelf life, so there's more spoilage. Traditional round, mature-green tomatoes are giving way to specialty tomatoes, such as Campari, on-the-vine, strawberry, romas-on-the-vine, and many others. Field grown fresh tomatoes now include grape tomatoes, mini-pear tomatoes of various colors, and extended shelf-life vine-ripe round tomatoes.

In general, she wrote, quality across all tomato types has improved. The better products are commanding higher prices.