How to tell when a soursop is ripe I purchased a soursop at the grocery store recently, because it sounded interesting and tasty.

I tried to make a smoothie with it, but it tasted very bitter and the fruit was very hard and crispy.  The soursop was dark green on the outside and solid white on the inside.  

I am determined to buy another, but I want to make sure it's ripe next time.  How can I tell when it is ripe?
I'm not sure I've had this exact fruit, but I've had similar fruits. They must be very soft. By the time they are ripe they will be soft and normally quite fragrant. But the best indication is that they are soft. If you push in, it will easily give and the skin will break. They usually don't sell them ripe because they would be damaged easily. You need to let them ripen at home.