Hopefully somebody with experience can answer that. I just googled "durian ripeness" and read suggestions like:
- it may crack on its own when ripe (mine didn't)
- it should smell some but not strongly until you open it (mine was like this)
- if you shake it you should hear soft thud of movement inside (mine was like this)
- scrape the stem and it should be green inside (mine was brown)
- push hard between spikes in the skin and it should give slightly (mine was like this)
Based on my humble experience growing up in Asia:
- it may crack on its own when ripe (mine didn't) --> this only happens when it ripe on the tree. Almost impossible to get the ones ripen on the tree this days, as they will turn bad very quickly except if you freeze them immediately.
- it should smell some but not strongly until you open it (mine was like this) --> yes, the smell it the first indicate when it ripes.
But some varieties don't have strong smell when it ripes, like Musang King.
- if you shake it you should hear soft thud of movement inside (mine was like this) --> yes, it indicates the pods separate from its shell.
- scrape the stem and it should be green inside (mine was brown) --> any fruit imported from Asia won't have green stem, it takes a month or so for shipment. But we never really scrap the stem in Asia to check the ripeness. The 2 signs above are usually used to detect durian's ripeness.
- push hard between spikes in the skin and it should give slightly (mine was like this) --> yes, it split easily when it ripe.
The best fresh durian I've ever tried in US is from China town in New York. The best frozen one is from my friend who imports frozen fruits from Thailand.
