Wet or canned dog food usually is packaged in a solid or soft-sided container. Wet food contains roughly 60-78% water, which is significantly higher in moisture than dry or semi-moist food. Canned food is commercially sterile (cooked during canning); other wet foods may not be sterile. Sterilizing is done through the process of retorting, which involves steam sterilization at 121 degrees Celsius. A given wet food will often be higher in protein or fat compared to a similar kibble on a dry matter basis (a measure which ignores moisture); given the canned food's high moisture content, however, a larger amount of canned food must be fed in order to meet the dog's required energy needs. Grain gluten and other protein gels may be used in wet dog food to create artificial meaty chunks, which look like real meat. This food is usually used for old dogs or puppies.