Pomegranates are grown on large bushes that drape like fountains. They get to be about four inches in size and have a "crown" on the bottom of them. Inside is a mass of membranes that aren't any good for eating and sacs of juice, pulp, and seeds that are quite tasty. For sweet fruit it is important that they be ripe. Under ripe fruit will remain sour or bitter and lack the sweetness and tastiness of ripe pomegranates.
Ripening on the tree.
The best way to ripen your pomegranates is right there on the tree. The pomegranate fruit will be ripe about seven months after it has flowered. You can test it by tapping on the outside of the fruit. If it makes a metallic type of noise it is likely to be ripe. You can then open it up. Ripe fruit is usually dark inside, but there are varieties that will be pale pink when ripe. Tasting at bit of the juice, pulp, and seeds will help you to determine whether or not the fruit is ripe because it will be sweet and juicy.
Ripening off the tree.
Ripening off the tree is somewhat problematic and not always a sure fire science. In most cases fruit that is sold in the store or at a farmers´ market will be picked after it is ripe because the pomegranate has a long shelf life. This allows farmers to pick the fruit after it is ripe, transport it, and sell it all over the country while still having a viable product for sale. However, should you have unripe pomegranates for some reason there are a couple of things that you can do to encourage ripening.
The first option is to place your pomegranates in a dry, cool place and wait it out. You will want to make sure that you are checking your fruit often to make sure that it isn't rotting. When it appears ripe, enjoy it. Most pomegranates can stay fresh for at least a month in a cool, dry place and some will last as much as two months.
Some people recommend ripening pomegranates in the sun. You do this by placing it in the window where it will get plenty of sun. Leave it there for a couple of days and check it by tapping on it. If it makes the metallic noise then it's ripe. You can then enjoy it!
Your best bet for ripening a pomegranate is to leave it on the tree. However, when that isn't a possibility you can try to ripen it in a cool, dry place or in the sun. Neither option is a guarantee, but you are likely to have some success.