If you feed coffee regularly be cautious about skipping the coffee ... they get cranky :)

With the brewed grounds most of the caffeine has already leached out. Never tried un-brewed grounds. The whole beans may take longer to break down in the bin.

People have been concerned about acidity in coffee grounds. With the UCG, most of it has been "brewed" out and make it relatively safe to feed to the worms. I'm not sure if it is the caffeine that cause coffee acidic.

It's definitely NOT the caffeine that is the source of acidity. Caffeine is an alkaloid. My guess would be the tannins in the coffee, but that's just a guess. Tannic acid (one of the polyphenols of the whole class of tannins) is a weak acid, but it could still be enough to lower the pH of bedding/compost.

Vegeburger, you might want to try to add a little calcium carbonate (egg shells would be good) to the coffee grounds. As for the caffeine, I have no idea if it would bother them or not. Is there any way you could sort of "pre-compost" the grounds for a week or so to get the caffeine out before the worms get hold of it?

L8r,
Don

Why not just brew the grounds and then use them? If they are old and you don't want to drink the coffee, you could always use it to water your plants.
I do know that whole coffee beans will take FOREVER to break down in a bin.

When adding URG ( used coffee grounds ) mix the grounds into the rest of the feeding. Before adding it to the bin. Coffee grounds in a pile get a little warm, just a little. But it is enough for the center of the pile to dry out. Then be shunned by the worms until it breaks down and gets wet inside.

I have found that even unblended food gets eaten faster if you stir it up before adding it to the bin.