It's the season for pumpkins and I was wondering if there is a way to tell if a pumpkin was going to taste good enough to cook with. I guess this is a similar situation as with a watermelon - you can't really cut it open to check if it will taste good.
Many of the varieties of pumpkin sold in US stores in the fall are decorative -- they're grown for their appearance and size, not for cooking with.
Ask for 'sugar pumpkins' or 'pie pumpkins' at your grocery store, farm stand, or farmer's market, and you should be able to find them -- they tend to be smaller, more squat than round (although, some farmers markets might have other varieties of "pie" pumpkins).
If you can't find them -- I'd go with acorn squash, instead of using one of the decorative pumpkins.
I think you're right that they're similar to a watermelon in that there's truly no definitive way to tell if they're ripe and good to cook with. There are a few signs you can look for though.
- Like a watermelon, thump it. It should make a hollow sound.
- Check the skin out. It should be hard like a shell. Press your thumbnail into it; it should resist puncture.
- Make sure the vine that is attached to the pumpkin has died and turned brown and woody. This is a good indicator that it is ripe and ready to be used.
An all-the-way orange pumpkin is a good indicator of ripeness, although with some brands of pumpkin the pumpkin can be ripe before being orange. Things to really look for are:
- The pumpkin sounds hollow when thumped (like watermelon)
- The skin dents but does not puncture when you push your fingernail into it
- The stem is hard
- There is a long stem (for eating this slows any rotting of the pumpkin)
If you are harvesting the pumpkin yourself, disinfecting the skin on picking will kill any bacteria that might cause rot. This is usually done with a 10% bleach solution. Curing a pumpkin for 10 days at 80 degrees F or so in a dark place will extend the shelf life as well.
Once you have purchased your pumpkin, store it out of direct sunlight at room temperature for maximum shelf life.