I have a class on composting coming in a month and a half... and books on the way... but we have excess grapefruits falling from our super high tree and I was wondering if they were ok to compost or if they make the ground acidic. I have looked but can't seem to find a simple list of what can go in. We're in FL so I have lots of fallen citrus.
From what I've read, citrus does not create a problem in compost. The peels might take longer to break down, but acidity should not be an issue.
I would chop them in half, because whole fruit do not break down readily until the peels are pierced, and would try to keep them from being over 10% of the total volume of the pile.
We do red worms (inside) and some people also use them outside--they don't like citrus-not sure if this is a factor or not for you
I'm a big citrus lover and throw lots of peels and the occasional rotten fruit into our pile. They don't take long to break down at all - a couple weeks, maybe, and I've never had pH problems in the garden where I use my compost. (I don't test the compost directly, though.) I would try to make sure there's enough other materials in the pile to keep the fruit buried, because of fruit flies, mold, and the high water content of the whole fruits.