Step into any specialty food shop and you'll encounter shelves of fancy vinegars and flavored oils. While the sleek packaging (such pretty bottles!) and infinite flavor combinations make them tempting purchases, it's far less expensive to make your own—and almost as easy as plunking down a credit card. Not only do they make excellent host/hostess gifts, we're seeing them in fine dining settings, too—AL's Place in San Francisco infuses oil with kuri squash peels and kale stems, and at a recent pop-up dinner in anticipation of his new restaurant, chef Bo Bech served an oil infused with pine needles taken from a tree in the lobby of the NoMad Hotel—that's right, Christmas tree oil. Here's how to make your own.
Your infused oil should be used exclusively for drizzling over soups, as a dip for good bread, and in vinaigrettes. You're not cooking with it, so skip the neutral, high-smoke point oils, like canola, vegetable, and grapeseed. Instead, use an olive oil that has a buttery, sweet flavor profile. Avoid olive oils that are grassy, herbaceous, and bitter—while those are great on their own, they don't combine with infused flavors well. Not sure what oils are buttery and neutral-tasting? Choose blended oils, rather than single-origin oils. Not only are blends less expensive, they are less assertive and strongly-flavored.
The sky's the limit when it comes to how to flavor your oil. There are two methods you can use to infuse the oil. The method you choose depends on the ingredients you're working with.
Cold-Infusion
This works well for fresh ingredients, especially tender ones, like parsley, cilantro, and fresh chile peppers. It's also the better option for very small ingredients, like peppercorns. Roughly one cup of loosely packed herbs per quart of oil is a good starting point, adjusting according to preference and strength of herbs (delicate parsley, for example, calls for more, while you can get away with just a sprig or two of pungent rosemary). To cold-infuse an oil, use a food processor to pulverize the ingredient, then mix it with the oil. Once the two have fully incorporated, strain out the solids. There's no need to let the infusion sit for a long period of time before straining, explains the Bon Appétit test kitchen staff, because there will be residual tiny particles left suspended in the oil that continue to flavor it. One thing to remember: Oil that's been cold-infused with fresh ingredients must be refrigerated. Rick Martinez, associate food editor says a fresh, cold-infused oil will last for about a week, so plan accordingly.
Heated-Infusion
Use this method for hardier, sturdier ingredients, like woody herbs (rosemary, thyme, and sage), and for dried/preserved items, like dehydrated mushrooms and chiles. Slowly and gently heat the oil no higher than 150˚—any more, and it will start to cook, changing the oil's flavor profile and potentially becoming rancid. Add the ingredients after the oil has been removed from the heat, and let it steep in a covered container. This doesn't have to be refrigerated, but know that the longer the oil sits with the ingredients, the stronger the flavor will be.
When you're ready to give the oil, use a funnel to transfer it to glass bottles (plastic will impart an off-flavor and besides, doesn't look as nice). You can do this immediately for cold-infusions, but remember to keep the bottle in the fridge until it's time to gift. You can also transfer heated oils along with the infusing agent to bottles immediately after they have fully cooled, but bear in mind: Some ingredients, like rosemary sprigs, can get funky and gummy-looking as their time in the oil goes on. If you're going to let it infuse for a week or more before gifting, consider removing the original infuser and adding a new one for a cleaner, more attractive presentation. The oil acts as a preserving agent, so that rosemary (or chiles, or garlic) won't go bad—but after sitting for a few weeks, it just won't look as pretty.
Not sure where to being? Here are some suggestions from the test kitchen:
Cilantro + serrano chiles
Lemon Zest + thyme
Chiles + garlic + orange zest
Assorted coarsely-ground peppercorns (pink, black, green, etc.)
Mint + lemongrass
Lemongrass + Kaffir lime
Rosemary + garlic
Fresh bay leaves
Ginger + garlic + lemongrass
Orange + lemon + lime + chile de árbol
Oregano + garlic + dried tomatoes (pizza-flavored oil!)