For many cooks (those not living in Southeast Asia, anyway), the hardest part about making Thai curry paste is finding a few of the ingredients. Some of what you need is waiting for you at your supermarket, but for the ingredients below, you may need to visit an Asian market.
A. Lemongrass (tah krai): With a floral lemony scent and a delicate citrus-like flavor, lemongrass shows off in a wide array of Thai dishes. It’s standard in curry pastes and valued in traditional medicines as well. It’s becoming more mainstream, so some supermarkets carry it, but Asian markets are a better bet for the freshest lemongrass. Look for sturdy, fibrous, pale-green stalks. To use, trim away the top portion of each stalk, leaving a 4-inch-long section, including the base. Pull off any dry, tired outer leaves before chopping or slicing as needed. To keep lemongrass fresh, wrap stalks loosely in a plastic bag and refrigerate them for five to seven days. To freeze lemongrass, trim the tops, wrap well to make them airtight, and freeze for up to six weeks. Use directly from the freezer without thawing. Avoid dried and powdered lemongrass, as they retain none of the flavor or aroma you need.
B. Galangal (kah): This cousin of ginger is prized for its extraordinary citrus-like flavor in soups and its burst of herbal heat in curry pastes. In its fresh form, its color ranges from delicate ivory to warm brown, depending on its exact variety and age. Round and plump with lots of thumb-like protrusions, it’s always encircled with small dark rings along the rounded chunks. Peel and chop it before grinding with other curry paste ingredients. Store fresh galangal loosely wrapped in plastic in the refrigerator for five to seven days. Or slice it thinly, arrange in a single layer in a zip-top plastic bag, press out the air, seal tightly, and freeze for up to six weeks (use frozen galangal slices without thawing them). You may also find dried galangal in large, woody-looking slices of wildly varying sizes. These work wonderfully in Thai dishes. Before chopping, soak them in warm water for 20 to 30 minutes or until pliable. Avoid ground galangal powder, as it lacks the intense flavor and aroma of fresh.
C. Shrimp paste (ka-pi): Profoundly redolent of all things oceanic, shrimp paste is an essential and treasured source of flavor and texture in curry pastes and in nahm prik, the beloved genre of hot chile dipping sauces. Made from tiny shrimp which are boiled, peeled, salted, dried, and then ground to a fine, sturdy, and very aromatic paste, it ranges in color from purplish-red to brown, with a firm but moist texture. It packs a powerful scent and super-salty flavor, but it melds into curry paste without a trace of its original intensity. Look for it in small plastic jars and keep it tightly closed until you need it. If it’s sealed with a layer of wax, simply break the wax and discard it. Store it at room temperature, tightly sealed, for up to six months.
D. Dried lime peel (piew mah-kroot): Essential in most curry pastes, the intensely aromatic and flavorful dried peel of the wild lime (also known as kaffir lime) delivers the vibrant citrus notes of limes and lemons with amazing depth. Drying sometimes turns the peel from vivid green to dull brown, but the intense flavor remains. Soak the peel in warm water for about 20 minutes or until it’s pliable and chop very finely before grinding with other curry paste ingredients. Store unused peel in an airtight container for up to six months. You may find frozen whole wild limes as well. Keep them frozen, and cut off strips of peel, including some white pith, as needed without thawing the lime. In place of wild lime, you can substitute lime or lemon zest, using the zest only, without the pith.
E. Cilantro root (rahk pahk chee): Milder in flavor and aroma than their leafy tops, cilantro roots provide a delicate herbal note and a plush, moist texture to curry pastes, bringing pungent ingredients like chiles, garlic, and galangal into a harmonious, flavor-packed whole. Look for cilantro bunches sold with their roots still attached. They may be tiny or up to several inches long. Use the root and about 1 inch of the stem portion attached to each root. Wash well and chop finely before grinding with other curry paste ingredients. To store, rinse well and put the roots in a jar of water with the leafy tops protruding from the jar. Keep at room temperature for one or two days, or cover loosely with a plastic produce bag and refrigerate for three or four days. You may also find frozen cilantro root in Asian markets. If you can’t find any cilantro root, substitute chopped cilantro stems with a few leaves mixed in.