I am going to try dry-hopping in the keg for the first time. I want to hang a nylon(?) bag from the corny keg lid. What size bag should I use for 5 ounces of pellets? Any other tips?
How much beer will this displace? I’m thinking probably a gallon. Turns a 5 gallon keg into a 4 gallon keg. Am I right?
Biggest tight mesh bag you can find. I find 5x7 bags are good for two ounces tops. Shouldn’t take up a gallon of space, quart tops.
Five ounces of pellets won’t displace much beer at all - maybe half a cup. It will absorb quite a bit more than that, but still not a gallon. You might lose a couple of pints to the hops.
FWIW, I use the regular 1-gallon Lowes paint strainer bags to dry hop…so far, so good. No significant hop matter from pellets at least.
What he said. The hops will displace the same volume as when they are pellets, but you will lose beer.
I never use a bag. Just throw 'em in!
In the keg that’s a recipe for clogged poppets. There is nothing worse than knowing you have 5 gallons of delicious beer that won’t come out!
Why would you dry hop in a keg? terrible idea! Just dry hop in primary after fermentation is over. With 5 gallons it’s great. You can cold crash to drop most of the yeast, then raise temp back up to 50-60s ina day or two and just throw your hops in then.
Keith, I dry hop American styles in a keg all the time in a 5 gallon paint strainer bag. No clogs, works perfectly fine. I just like to trap the hop aromas in the keg. But I use buckets, so I don’t closed transfer from the fermenter to the keg. With that setup, it gives me what I’m after - good hop aromas that don’t get oxidized on the way to the keg.
That makes sense if you are purging the keg first. Now I get it. I do similar when I dry hop in large fermentors. I either fill a yeast bring with dry hops, purge with co2 and the pump into beer or dry hop in another purged fermentor and then rack beer onto those hops.
carry on gents, yer way ahead of me. 
But yes, in any other situation I just throw the pellets in.
Yep, I definitely purge.