There are two ways to get this done, dry-aging and wet-aging. The difference between them comes down to how the meat is treated during this resting period. Dry-aged beef hangs out uncovered in a temperature- and humidity-controlled room. Because it's exposed to oxygen, the exterior of the meat develops mold, which helps to protect the meat within. Still, chefs need to cut off these moldy parts, resulting in a 20 to 30 percent loss of the original product. Conversely, wet-aged beef is sealed in plastic and then stuck in a fridge. Because it's not exposed to oxygen, none of the meat needs to be removed before cooking.