I love the idea of using this as a way of using fruit that's close to being past its prime - before it's too late. I hadn't thought of it that way but am eager to use more ways of wasting less, especially since I'm only cooking for 2 usually. Thanks for the suggestions!

I would actually disagree with betteirene (sort of). If you're buying the fruit specifically for the rumtopf, you could follow her directions, but preserving it in sugar and alcohol is my favorite way to deal with fruit that is maybe a little softer/riper than I want to eat. I'll slice up slightly overripe strawberries or peaches and throw them into a jar in my fridge with sugar and rum or brandy. It's a great way to cut down on waste, and the results make an ever shifting and completely delicious topping for ice cream or pound cake.

Not-quite-ripe is better than over-ripe. You want ripe but not soft, and you certainly don't want to preserve mushy spots or bruises. You're going to cut the fruit anyway, so taste a slice of each one; if it's toothsome without being crunchy, if the sweet ever-so-slightly outweighs the tart, start it now.