1. Only the top grades of beef can be dry-aged successfully. Use USDA Prime or USDA Choice - Yield Grade 1 or 2 (the highest quality of Choice) only. These have a thick layer of fat on the outside to protect the meat from spoiling during the aging process. Ask your butcher if they can hang your beef for 7 days prior to purchasing. This will give you a head start, allowing you to age the beef a maximum of 14 days in your home refrigerator.
2. Buy a whole rib-eye or loin strip. (You cannot age individual steaks.) Unwrap it, rinse it well with cold water and allow it to drain. Pat it with paper towels until very dry.
3. Wrap the meat in immaculately clean, large, plain white cotton dish towels and place it on the bottom shelf of the refrigerator - which is the coldest spot. A small fan to move air around beef is optimum, but not required.
4. Change the towels each day, replacing the moisture-soiled towels with fresh ones. Continue to change towels as needed for 14 days. (See Step #7 for cleaning towels.)
5. After the desired aging time of 14 days, you're ready to cut off steaks from each end, trim as desired and allow the rest to continue to age in the refrigerator.
6. If, after 21 days, you have not eaten all the meat, cut the remaining piece into steaks, wrap each steak in freezer-proof, heavy-duty plastic wrap, and freeze. The steaks will keep for several months in the freezer.
7. To clean the towels for re-use, soak the soiled towels, immediately upon removing them from the meat, in cold water overnight. Next, soak them in cold, salted water for 2–3 hours to remove any blood stains. Then launder as usual. (In olden days, butchers used to cover sides of beef with cotton "shrouds" or cheesecloth during the aging process - this is essentially the same thing.)