Some dried spices are no substitute for fresh versions
Knight Ridder Newspapers
Q: A lot of recipes these days call for fresh cilantro and fresh ginger root. What are the dry substitutes?
A: The standard advice is to substitute one-third the amount of dried spices or herbs for the fresh. But ground coriander -- the dry form of cilantro -- tastes nothing like fresh. We'd hesitate to substitute it in a recipe that calls for more than a tablespoon of fresh cilantro.
Powdered ginger may be substituted for fresh ginger in some recipes. The dish won't have the vibrant flavor that fresh ginger imparts. You can buy fresh ginger and freeze the leftovers, tightly wrapped in foil. Unwrap it and nuke it in a microwave for a few seconds to thaw it out. The thawed ginger will be slightly mushy but will taste better than powdered ginger.