While this link has some good background information, it's not good for someone looking for specific instructions for aging beef at home.quote:
He refers to using a humidity level of 80-85%. That's way out of range, and it will result in high levels of surface moisture.
Excess surface moisture will enhance bacterial activity, increasing the possibility of pathogen growth and food poisoning.
Dry aging works by denying bacteria the moisture it needs to survive and grow. By keeping the humidity below a certain level, the surface will become dry and bacteria will be inhibited.
Conversely, a high level of relative humidity leaves the surface wet and increases the probablity of bacterial growth.
At 85% humidity, the surface will not dry properly. It's so high that moisture will actually bead up and collect on the surface of the meat. The low airflow environment of a home refrigerator will amplify the problem.
For home aging, I recommend keeping it to a 60% maximum. At that level the meat will begin to dry within a day, and will form a slight crust within 3 days.
You can go as high as 70%, but I wouldn't do it without using special equipment. I've been dry aging beef continuously for years, and I use a data logger set at a 5 minute sampling interval. If the temp and/or humidity go out of range it sets off an alarm.
dls's recommendation of using a dedicated fridge is also right on. It's very difficult to ensure you don't go out of parameters otherwise.
I'm not sure where the author got the 85% number. Maybe it's a typo, maybe it's intended for professional producers who use it in combination with ultraviolet lighting, enhanced airflow rate, etc. I don't know. I can say that it's out of safe range for a home cook.