How to do a beer-butt chicken?
If you google beer can chicken, you will find many, many recipes and descriptions.

The basic idea is that you use a half-empty beer can as stand for the chicken, placing the chicken's cavity on top of the can before roasting or grilling.

The idea is that the aroma from the beer will transfer to the chicken, and the steam will help keep it moist.

You can even buy commercial racks to do the same thing without the beer can.



My personal opinion is that both of these ideas are bunk:


Very few if any aromatic molecules will transfer to the chicken, and even if they do, they will not penetrate past the surface
The steam will not keep the chicken moist, as the dryness of the meet is essentially a function only of the temperature to which you cook it, and very little else.  If the chicken is cooked to too high a temperature, then the proteins will tighten up and express water making the chicken tough, rubbery, and dry tasting.   The minimal amount of steam cannot change this fact.