However, some sites also said that freezing persimmons to ripen them was a myth, and that patience was the only real way to do it. I couldn't find a definitive answer, so I decided to put it to the test.
30 minutes after eating the persimmon, I started to get a pretty bad stomach ache, which still hasn't completely left me 3-4 hours later. The persimmon didn't taste astringent, so I thought all of the tannins had been denatured by freezing. However, it still had an astringent aftertaste, so maybe there were still enough tannins to make me feel sick, even though the fruit was palatable.
So either I didn't freeze it long enough, or freezing persimmons to ripen them really is a myth and the persimmon I has was already semi-ripe.. Based on how I feel right now, I won't be testing the 'freeze it longer' hypothesis. I'll let someone with a tougher stomach take on that one. I'll confer with with the experts on the fruit forums, and post any new developments. For the time being, I'll ripen the rest of my persimmons by letting them sit on the counter until mushy.
UPDATE - 11/15/2010:
I froze another persimmon, thawed it, and then left it in the freezer over the weekend. I pulled it out today and popped it in the microwave for 1 minute. Same result as last time, astringent aftertaste followed by nausea. At least I didn't eat the whole thing, just a few wary test bites. Soda seems to help with the stomach ache.
I'm very disappointed because I really want to like persimmons. I've already got two persimmon trees, and they fruit at a time when not much else is available. I've got one more persimmon ripening on my desk at work. I'll try it when it is super mushy, and hopefully it won't make me sick. If it does, I may have to just forget about persimmons altogether and replace those trees with something else.
UPDATE - 11/17/2010:
Glen Miracle very generously gave me three non-astringent Fuyu persimmons at the City Hall Farmers Market today. Now these are good. Really good. Nice and crisp, really sweet, with no astringent aftertaste. And even more important, no nausea or stomach ache. Glen's Fuyu's are much much better than the ones HEB was selling for $2.50 each. Those were sweet, but kind of rubbery, and they didn't look like they had ripened before picking. Glen's are bright orange red, and I look forward to finishing them off with Joe tonight. I still have one of his Hachiyas ripening on my desk, I'll post an update when I try it.