Garlic powder gets no respect. Sure, the aroma and taste of fresh garlic is hard to beat, but in some situations, the dried stuff doesn’t just measure up, it flat-out wins. If you need a garlicky vinaigrette, marinade, or dip to taste great for longer than 24 hours, powdered or granulated garlic is the way to go.
The best reason to use dried garlic in sauces is that it actually improves with time. You know how anything with minced raw garlic gets that distinctive “old garlic smell” after a couple days in the fridge? That doesn’t happen with granulated or powdered garlic. (As a bonus, neither does botulism.) The dried stuff still tastes and smells plenty garlicky, but the sharpest, most aggressive flavor compounds—which also happen to go off the fastest—don’t survive the drying process. Thus, using granulated or powdered garlic (or both) gives you all the benefits with none of the downsides.
And you should definitely use both. Believe it or not, there’s a big flavor difference between granulated and powdered garlic. Granules add a potent, super-garlicky punch that’s similar to raw minced garlic, while garlic powder has a deeper, rounder, more savory flavor. Using some of each adds a ton of complexity with basically zero effort, which is why I always keep both on hand.
Swapping granulated or powdered garlic for fresh is pretty easy, but when it comes to quantity conversions, you’ll have to fake it ‘til you make it. No two garlic cloves are exactly the same size, and the potency of dried garlic varies wildly by brand and age; figuring out an exact formula is basically impossible. As always, season to taste until you get a feel for what you like. Just keep in mind that a little goes a long way, especially with garlic powder, which is about twice as dense—and twice as intense—as granulated.
If you’re wondering whether all of this also applies to dried onion products, it does—kind of. I just don’t think dried onion products work any better than fresh in this specific application. The flavor you get from using a combination of sweated, caramelized, and straight-up burnt onions is way more interesting than onion powder, and raw onions tend to age gracefully in acidic vinaigrettes. Your mileage may vary, but personally, I’d save the onion powder for Live Más Dust.