Hi Stuart,
The b.linens (the orange bacteria), like the moisture. Usually, washing starts about a week after the make. I've not done a beer wash myself as I usually just use brine, but presumably the principle is the same. Add salt to get it around 3-5% solution (i.e. 95g beer and 5 grams salt gives you 5% by weight). I would think it would be best to let the beer go flat as well. Not sure if there's anything you need to do concerning yeast in the beer though. Anyway, if you've added b.linens to the make you shouldn't need to add any to your wash, but it wouldn't hurt.
Keep these isolated from other cheeses, especially mouldy ones. You want the linnes to develop and don't want wild moulds to interfere. Make sure you sterilize your ripening container well, doubly so if you've used it for cams or blue cheeses.
Oh, and photos are a must.
- Jeff