How can I know when a kiwi fruit is ripe?

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For cinco de mayo I was making a jello dessert. On top on one third of the dessert was supposed to be sliced kiwi fruit.I bought the kiwi at the store. Brought it home and sliced it and it was so bitter it was not ripe at all. This was May 5th. It is now May 18 and I figured it would have to be ripe by now even though the outside of the fruit was still hard. I sliced into it and it was still terribly bitter and not ripe. Does it usually take this long to ripen? Before cutting into it and ruining it how can I tell if it is ripe? Will it be soft feeling like an orange or by then will it have gone bad? I havent had a kiwi since I was in high school when my friends mother let me have a slice. It was so good I was really hoping to eat these.