Modern corn has been bred to stay sweet and tender longer, but it's not invincible. You need to refrigerate it as soon as you get home and use it within two days. If it becomes tough in spite of your best efforts, however, don't throw it out. Canning and freezing old corn do not improve its quality and you'll be disappointed with the results. However, you can cook the corn with tasty liquids to soften it.
An old Southern technique for tenderizing corn calls for cooking bacon in a skillet until it's crisp, the transfering the bacon to a cutting board and crumbling it. In the meantime, you add the corn to the skillet, along with some milk, salt and pepper, dill and green onions. Simmer -- don't boil -- the corn until the milk is mostly absorbed. If the corn is still tough, add a bit more milk and continue to cook. As the corn absorbs the milk, it regains its tenderness. Toss the bacon with the corn for a savory dish that makes a fine accompaniment to fried or roasted chicken, pork chops or pulled pork.
Tenderize corn that's past its prime by adding it to a rich, savory soup. As the corn soaks in the warm broth, it becomes tender, but allowing the soup to boil will toughen it further. Pureeing the corn as you would to make corn chowder further tenderizes it by breaking it down. The soup will have a rich corn flavor while disguising corn's toughness. Use old corn in chicken tortilla soup, minestrone or corn chowder.
In the Pot
Overcooking is a common reason for tough corn. There's not much you can do to remedy corn that's been overcooked, but a bit of care at the beginning will prevent this problem. Heat water in a pot to boiling, add the cleaned and shucked corn and turn off the heat. Cover the pot with a lid and set the timer for five minutes. When the time's up, remove the corn from the water promptly. It will be bright yellow, but juicy and slightly crisp. For extra sweet corn, add a teaspoon of sugar to the water. Slather the corn with butter, salt and pepper and serve immediately.
At the Store
Getting the freshest, tenderest corn starts at the grocery store or farmer's market. Buy corn when it's in season locally, typically late summer. At other times of the year, the corn has been shipped across the country and won't be as fresh. Look for large ears with sticky, brown silk. If the silk is black or slimy, you know the corn is old. The ears should feel firm and well-filled. Pull back the husks slightly from one ear. The corn should look plump, never shriveled or dry. If you stick your fingernail in one kernel, white liquid should spurt out. You don't need to test each ear using this method. If one ear is fresh, the rest of the corn should be fine too.