A jurymember, before participation has to provide a preferential 20 categories list, in order of preference, to the organisers. In fact, this will be reckoned with to assign him/her the categories. But it will be in no way exclusive: the organisers alot all 85 categories, and one is assured a few that won't be exactly what asked for. I fear otherwise, not many low-carb American lagers or malternatives would get judged. Mind you, no jurymember can judge a category in which a brewery/distributor/group he's interested in professionaly, has entered one of their beers. Obviously.
The categories one's assigned are divulged the evening before the first judging at the jury's orientation.
In the stewards' room, the steward captains assign each entered beer a specific codenumber. The jurymembers only judge numbers, not names. This stewards' room is strictly out of bounds to anybody judging, and I can assure you this rule is enforced.
A judging of one category gets done this way. Depending on the number of entries, a category is divided over one, two, three tables of each six to eight judges. If many entries exist, in a first round the number is divided in two flights (say eight beers) pro table, each discussing the merits of the 8 beers. This three/four judges taste each beer (from which he has only a number on the small tasting cups), and fill in a standardised form of tasting notes, in which we are urged to fill in as many short observations as possible (these notes are in duplo). Then we start discussing, in most cases starting with eliminating the most obvious failures, though not necessarily so. Each flight sends forward three beers, which go to the next/final round. The eliminated beers go, with a generally agreed upon verdict by all the judges having tasted it to the brewer, who can assess what we thought wrong about it. If nothing's really wrong with it, or the jurymembers were a bit divided, the formula indicated on the jury verdict is "essentialy a quality beer, but better entries were on the table", which is supposed to put some balm on a disappointed brewers' heart. Each jurymember has an assigned (non-alphabetic!) codenumber, preprinted on the form, so the organisers, but not the brewers can know who wrote what.
In the final round, there's no more individual formulars. The beers, having come in from the former flights/rounds are again brought in, but bearing another codenumber, not linkable to the one given to it before. This time, the full table of judges taste all beers in the running.
The emphasis (for gold) is more on which beer is really the epithomizing of the style, faultless. In fact, in the formula indicating what means "bronze", and what means "silver" medal I personally think too much is accented on that there might be anything not 100% right with those. In fact, it is about which most jurymembers like best. But I can see the reason: sometimes, as this year, some categories just didn't deserve some medals - in one case even the gold was not attribuated. Ex-aequo's, however, are out of bounds.
The fights under jurymembers on this final medal-giving can be heroic, halting only at personal violence ;^}. In fact, they can be great fun to be in (or to watch, ask the stewards).
On what goes on in the rooms, the best to ask would be either Carl Kins (as he figured some years as steward before turning coat, sorry, judge) if he could be persuaded to come here a bit more; or also Mitch Mather, who is one of the legendary serving stewards. I cannot formulate an opinion, as I never was in. There were some minor mistakes this year, but I remember Denver GABF 2003, where the stewards' work was simply flawless.
Judges are provided with pens, paper, plain water and matzes (for palate cleaning purposes) by the ever-watchful stewards, and the most prized possessions are staples and staplers (half joke). Cellphones are banned.
I could probably go on for another few pages, but I can you can all get the picture.
I have been very apprehensive about the whole procedure, but having gone through it now twice in this system, I can vouch that is near watertight, as much as that is possible. I have had other judgings, both for CAMRA CBoB and for commercial purposes, and I can assure you there is as good as no opportunity to influence a judge at the table.