It is notoriously difficult to trace the lineage of modern citrus fruits. The total number of citrus species is unknown, and nearly all of them are capable of breeding with one another, which has resulted in a never-ending list of hybrid fruits. The mandarin is thought to be one of the original parent species, along with the citron and the pomelo. Over the course of thousands of years, these three trees collectively gave rise to Meyer lemons, grapefruits, kumquats, limes, and all of their family members.
Mandarins probably originated in northeastern India. The fruits were first exported to the West via Tangier, Morocco, which led to the popular name "tangerine." Today, the term "tangerine" can refer to mandarins with orange-red skin and a squat shape, but the name itself has no real botanical significance.
I find the simplest way to categorize mandarins is by grouping them into early, middle and late season varieties. This method makes the most sense for a cook. From somewhere around Thanksgiving to New Years Eve, look for early season varieties such as the Satsuma, which is tangy, usually seedless, and delicate. From Christmas through March, middle season varieties reach their peak. One of these, the Clementine is perhaps the most well known mandarin, and its popularity is rising. Increasing numbers of imported Clementines come from Spain, but some of the juiciest, most aromatic Clementines are grown in the Mediterranean-like climate of San Diego County. As the season draws to a close, from March to May, choose the Pixie. This late-season variety, no bigger than a ping-pong ball, grows extraordinarily well in the areas surrounding Ojai. Pixies were initially a tough sell to supermarkets because of their petite size, but were quickly scooped up by chefs and soon became a Southern California farmers' market favorite.
Unsurprisingly, there is one mandarin that doesn't quite fit into these seasonal groupings. If you can get your hands on any walnut-sized, seedless Kishus, buy as many as possible. They are grown by just a handful of farmers in California, their season lasts for only the month of January, and their flavor is superb.
Black Cod and Mandarin En Papillote
Cooking fish en papillote, or in parchment paper, is a wonderful way to seal in the juices, and it also happens to look festive. You can assemble these fish packages earlier in the day and bake them just before dinner. This recipe is easily doubled or halved.
4 ounces (about 6 cups) baby spinach
4 5-ounce black cod fillets
4 teaspoons rice vinegar
4 teaspoons extra-virgin olive oil
2 teaspoons finely grated fresh ginger
4 small mandarins, peeled and pulled apart into segments
1 clove garlic, peeled and thinly sliced
½ teaspoon cayenne
½ stick (4 tablespoons) unsalted butter
Kosher salt and freshly ground black pepper
Preheat the oven to 425°F.
Cut 4 pieces of parchment paper, each about 20 inches long. Mound 1½ cups spinach in the center of each paper. Place 1 fillet on top of each mound of spinach, and drizzle each fillet with 1 teaspoon rice vinegar and 1 teaspoon olive oil. Spread the ginger evenly across the fish, scatter the mandarin segments and garlic, and sprinkle the cayenne among the fillets. Top each fillet with 1 tablespoon butter and a generous sprinkling of salt and pepper.
Fold parchment over fish, making small but tight pleats around the edges to seal. Tie with twine. Repeat with remaining parchment. Transfer the packages to a rimmed baking sheet, and bake for 15 - 22 minutes, depending on the thickness of the fillets. They should puff up with steam. It's okay to peak inside to check if the fish is done cooking; just be sure to seal the parchment again.
To serve, place packages directly on each of 4 plates. At the table, untie the twine and cut open the parchment, being careful to avoid the hot steam.