A shucked ear of corn only needs to cook for one or two minutes. Bring fresh, salted water to a rolling boil and add the corn. When the ear is warmed through, it's done.
Traditional cookbooks may recommend boiling corn for five or even ten minutes, but modern corn is much sweeter than in the past. Too much heat converts the sugar molecules into starch, resulting in too-soft kernels that have lost their sweet flavor.
The sugars in an ear of corn begin converting into starch as soon as it is picked. For the best results, use the freshest corn available.