Like oysters and princes, herbs are nearly always at their best when they're fresh. But we've all been there: you buy a bunch of parsley from the supermarket for those two tablespoons of garnish that you need, a week goes by, and you suddenly find yourself with a whole lot of fresh parsley that's on its way out. What do you do? The best option is to just find a recipe that uses it, of course. You might also consider blanching and freezing it in ice cube trays.
Or you might want to dry it. Drying herbs will greatly extend their shelf life by removing any moisture that bacteria could use to survive. The downside is that it also robs fresh herbs of flavor, aroma, color, and texture. But there are ways to mitigate this loss. Your best option? The microwave. Yes, really. It's a trick I picked up from Daniel in his holiday story about spiced nuts.
Compared to other drying methods—like hanging or using a low oven—the microwave produces the most potent dried herbs with the freshest flavor and the brightest color.
What Herbs Can I Dry?
When it comes to picking which herbs to dry you've also got some decisions to make. In general, thick-leafed, hearty herbs that grow in hot, dry climates like rosemary, thyme, savory, marjoram, and oregano fare well with drying. This is because their aromatic compounds are naturally less volatile than their more delicate, fair-weathered counterparts. They have to be. If they weren't, they'd lose too many volatiles through evaporation under hot and sunny conditions.
Dried hearty herbs can be used very much like their fresh counterparts for flavoring roasts or sautés, for sprinkling into soups or on your pizza, or for stewing and braising.
Delicate herbs should be used for dishes that use moist cooking methods like soups, stews, and braises. They can take on a papery texture if used where fresh herbs would be used such as for salads or for garnishing. I wouldn't recommend it.
So what makes a microwave so much better at drying than any other method? A few factors.
Microwaves Preserve Flavor and Color
What's different about the microwave than other methods of drying? The main thing is that microwaves specifically target water as they're heating. Microwaves work by emitting waves of long electromagnetic radiation that cause polar molecules within your food to rapidly flip back and forth. By far the most abundant polar molecule in anything we eat is water. So really, a microwave doesn't heat up all your food, it just heats up the water. The hot water in turn transfers energy to the rest of your food. An oven, on the other hand, heats everything evenly.
What this means is that a microwave can very efficiently case water to evaporate from your herbs—especially because they are so thin—while leaving flavorful compounds and colorful pigments mostly intact. Herbs that would end up brown or gray and flavorless by the time they're done drying in the oven or through hanging will retain their bright green color and much of their aroma after the minute or so it takes to dry them in the microwave.
Just look at this rosemary. The batch on the left was dried in the microwave while the batch on the right is fresh.
See how much color is preserved? You can't taste it, but there's as much flavor as there is color in there. And because microwaved herbs are so brittle and dry (air- or oven-dried herbs tend to be more tough than brittle), they can be reduced to fine, flavorful powders that incorporate beautifully into spice blends and rubs. Try these Olive-Rosemary Spiced Cashews, for instance.
Microwaves Are FAST
Microwaves are by far the most efficient method of heat transfer in your kitchen. You can take a batch of fresh herbs from the fridge to the dry pantry in just a couple of minutes—a fraction of the time it takes for your oven to even pre-heat!
Convinced yet? Here's how to do it.
How to Dry Herbs in the Microwave
Step 1: Spread the Herbs
Pick the leaves off the herbs and spread them on a microwave-safe plate lined with 2 layers of paper towels or a clean kitchen towel.*
*Do not microwave recycled paper towels—they can contain tiny fragments of metal that can arc and cause fires.
Step 2: Cover and Microwave
Cover the herbs with a second paper towel or clean dish towel, then microwave them on high power. Most hearty herbs will take around 1 minute initially, followed by a few 20 second bursts until completely dry. Delicate herbs will take 40 seconds followed by a few 20 second bursts until completely dry. All of my timing was done with a half ounce of fresh picked herbs (about as much as can fit on a dinner plate in a single layer) in an 800-watt microwave operating at full power.
Herbs should crumble when you bend them when they're finished. If the herbs are still pliant, continue cooking them until completely dried.
Step 3: Store or Grind
Once the herbs are dry, you can store them whole or grind them into a powder for spice rubs or spice mixes.
I use either a mortar and pestle or a coffee grinder to reduce the herbs to powder. If you want it extra-fine, you can tap it through a fine mesh strainer. Whether left whole, crumbled, or in powder form, dried herbs should be stored in a tightly sealing airtight container in a cool pantry away from light. Stored this way they'll last for several months while maintaining flavor and color.
I've tried the technique to great success with every commonly available herb in even the fancy supermarkets and while I'll still stick to fresh herbs on a day to day basis, it's a relief to know that I have a good alternative whenever I find myself in a glut.