The flavor of beef is greatly improved by proper aging. "Aging" usually refers to the time, in days, from slaughter until the carcass is broken down into retail cuts. In America, the average industry time for aging is about 7 days. However, true beef flavor is only fully developed after about 11 days of aging. Aging also makes the beef more tender. Cooked, unaged beef is said to have a flavor often described as "metallic" and lacking in any typical beef taste. I first learned about this when I was living and working on a cattle ranch. The beef that we sent to the slaughterhouse for our own use (rather than to sell) was always "hung" at least 10 days. (While aging, the beef is generally hung from huge meat hooks in special cold rooms.) Properly aging the beef enormously improves the flavor and texture, but aging it longer ends up costing more for several reasons, so commercial beef generally isn't aged long enough to develop full flavor. You can read about what aging actually does to beef and some of the impact it has on the cost of beef here: http://www.extension.umn.edu/distribution/nutrition/DJ5968.html Like beef, lamb should also be aged for best flavor. Pork should never be aged, but should be cut and wrapped within 24-48 hours of slaughter, for health and safety reasons. Chicken flavor is best when the chicken is freshest. This is also true of fish and seafood.