How do I know what spices I can use dry vs. going out and having to buy the real deal?

In general, most herbs can be used in both fresh and dried forms. However, the flavor can significantly differ. Dried herbs have a concentrated, more robust flavor, while fresh herbs have a bright, vibrant taste.

Herbs like cilantro and basil are usually used fresh because drying can significantly alter their flavors. These herbs have volatile compounds and oils that provide their characteristic flavor but are lost during heating.

• This is why you want to add fresh basil & other delicate herbs at the end of the cooking process. Stewing them too long “cooks out” their fleeting aromas.
• Try this for yourself in this basil beef stir fry — mixing in basil at the end is all you need to perfume the dish.

On the other hand, hearty herbs like rosemary, thyme, and oregano retain their flavor well when dried due to their less volatile aromatics. Here’s a nice summary:

Don’t clear out the spice cabinet quite yet, though:

• You can keep dried basil around for convenience, but it won't give the same flavor as fresh basil. We think it gives that generic “pizza sauce” aroma, which is great in some cases, but not really a close substitute for the fresh leaves.
• Dried chives could maybe be used up in a sour cream & onion dip deal, where they’ll be rehydrated a bit and add specks of green color.

Dried cilantro, mint, and parsley aren’t as useful, however. Next time a recipe calls for those, go find the real deal.