How to Keep Your Jack O’Lantern Looking Dapper Longer
1. First and foremost, pick a pumpkin that is hard. Also, make sure that it has no blemishes. You dont want them to have any frost damage, says Andres. You can tell that by looking at the fruit. Watery dark spots on the top of the pumpkin are an indication of frost damage.
2. You want to wait until the last moment before carving pumpkins, says Andres, since they tend to rot within a week or so. But once you carve them, there are a few tricks to making them last a little bit longer. You can squirt lemon juice on the exterior of the pumpkin, for instance. Lemon juice, as you may know, prevents the browning of fruits, such as apples and avocados (and pumpkins!). The browning is a result of phenols and enzymes in the fruits reacting with oxygen, but acidic lemon juice blocks the enzymes and thereby inhibits the reaction. Vaseline or vegetable oil can also be applied to preserve the pumpkin once it is cut.
3. Spray the jack olantern with a bleach solution, to stave off fungus growth.
4. Keep the pumpkin away from freezing temperatures. If it freezes, the pumpkin will thaw and inevitably rot.
http://blogs.smithsonianmag.com/artscience/2012/10/keep-your-jack-olantern-looking-dapper/?utm_source=smithsoniantravandcult&utm_medium=email&utm_campaign=201210-travel