At first glance, Okinawan sweet potatoes look pretty ordinary. The skin of this starchy root vegetable is thin, dull, and beige. However, slice one open and you’ll find that the insides are a marvelous violet! When cooked, the color intensifies and ranges from mauve to dark purple. Similar to their orange counterpart, Okinawan sweet potatoes are delicious and versatile. Roasting yields a creamy texture and a slightly sweet, earthy, and nutty flavor. Like blueberries and eggplants, Okinawan sweet potatoes contain anthocyanin, the pigment that gives these foods their natural purple color. Anthocyanins are powerful antioxidants with numerous health benefits. Sources indicate that Okinawan sweet potatoes have 150 percent more antioxidants than blueberries!
The high concentration of anthocynanins consequently created an interesting baking challenge. My attempt to make Okinawan sweet potato scones inadvertently turned our kitchen into a mini laboratory. For my first batch of scones, I opened the oven door to find that my gorgeous purple dough had turned greenish blue! Had I paid more attention in chemistry class I might have remembered that anthocyanins are pH dependent. When exposed to different levels of acidity or basicity, anthocyanins change color. Thus, the absence of an acid and a high pH (too much baking powder & baking soda) in my scone batter produced a green baked good. After a few failed attempts, I finally got the recipe right. I increased the acidity via homemade coconut buttermilk (coconut milk + white vinegar) to lower the recipe’s pH. The final result? A mouthwatering scone laced with glorious chunks of dark purple sweet potato. To finish, I topped each scone with a drizzle of lavender colored icing, made from blended sweet potato, coconut milk, and powdered sugar.
The how to…
Recipe adapted from Cook’s Illustrated
15 2 1/2 inch round scones
1 cup mashed sweet potato, about 3 small Okinawan sweet potatoes
1 egg, beaten
2 1/4 cups all-purpose flour
2 tsp baking powder
1/2 tsp baking soda
1/2 tsp salt
1/3 cup granulated sugar
6 Tbsp frozen unsalted butter, diced
light coconut milk, for milk wash
1 cup light coconut milk
1 Tbsp distilled white vinegar
Okinawan sweet potato glaze
1/2 cup powdered sugar
1 Tbsp roasted Okinanwan sweet potato
1 Tbsp light coconut milk
- Make sweet potato mash. Preheat oven to 400 degrees. Wipe potatoes with a damp cloth and prick with a fork. Place directly on oven rack and roast until soft, about 50-60 minutes. Carefully remove from oven and let cool completely. Scoop out the insides and mash (1 cup is needed for recipe). Set aside.
- Prepare coconut buttermilk. In a small cup, combine coconut milk and vinegar. Let sit for 10 minutes.
- Wet ingredients. In a medium bowl combine coconut buttermilk, sweet potato mash, & egg. Whisk until well incorporated. Set aside.
- Dry ingredients. In a separate bowl, combine flour, baking powder, baking soda, salt, & sugar and mix well. Add diced butter and cut into flour with a pastry blender or fork until mixture is crumbly and butter resembles small pebbles.
- Combine. Add wet mixture to flour mixture and fold until just combined. Turn dough out onto a floured counter and dust surface of dough with flour. Using floured hands, knead dough 6-8 times (add flour as necessary to prevent sticking) until dough comes together into a ball. Dust dough with additional flour and roll out with a rolling pin. Stamp out rounds using a biscuit cutter and place on a sheet pan lined with parchment paper. Lightly brush the tops with coconut milk and bake in a preheated 425 degree oven until golden brown, about 25 minutes. Remove from oven and let cool completely.
- Glaze. Combine glaze ingredients in a blender (I used a Bella Rocket Blender) and process until smooth. Drizzle glaze over scones and serve.
*Sweet potato mash can be made up to 2 days in advance. Store in refrigerator until ready to use.
*Any tinge of green that might appear in the batter (due to the chemical reaction noted above) should disappear once the baked scones are allowed to fully cool.
*In NYC, Okinawan sweet potatoes are available in Asian markets in Chinatown.