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–+ servings

Sweet Potato Tempura (3 Japanese Ways to Make)

Prep Time15 minutes
Cook Time15 minutes
Chilling Time30 minutes
Total Time1 hour
Author Yuto Omura
Servings 4 portions

Ingredients 
 

Sweet Potato

  • 600 g Japanese sweet potatoes a cream-fleshed variety is the closest match
  • cooking oil neutral with high-smoke point

Tempura Batter

  • 75 ml cold water thoroughly chilled
  • 50 ml carbonated water thoroughly chilled
  • 15 g cornstarch
  • 75 g unbleached cake flour or pastry flour, low-protein, around 7-8%
  • 1 egg yolk or ½ tbsp Japanese mayonnaise for 1 yolk
  • unbleached cake flour for dusting
  • 2 ice cubes optional

To Serve

Instructions 

  • Chill 75 ml cold water and 50 ml carbonated water in the refrigerator for 30 minutes. Sift 15 g cornstarch and 75 g unbleached cake flour into a bowl and chill the bowl for 30 minutes in the freezer.
    Still water in a jug and sparkling water in a sealed bottle
  • While they chill, scrub 600 g Japanese sweet potatoes and trim 1 to 1.5 cm off each end. Leave the skin on and cut to your chosen shape. Thin rounds or diagonal slices 8 to 10 mm, thick rounds 25 to 30 mm, sticks 10 to 12 mm square. Each stick keeps 1 face of skin.
    cutting Japanese sweet potatoes into sticks for tempura
    • For thick rounds, shave the corners flat and score a shallow cross into both faces, about ⅓ of the way through.
  • Drop the pieces into cold water as you cut, 3 to 5 minutes for the thin cuts and 5 to 10 minutes for thick rounds. Do not soak them longer than this.
    soaking cut Japanese sweet potato in a bowl of cold water
  • Pour cooking oil into a heavy pot and start heating. Set 165 °C (329 °F) to 170 °C (338 °F) for thin rounds, diagonal slices and sticks, and 160 °C (320 °F) for thick rounds. Keep the cut sweet potato at room temperature.
    heating oil in a pot to make tempura
  • Pour the chilled waters into a bowl and add 1 egg yolk. Gently whisk until incorporated.
    whisking egg yolk and chilled water in a bowl to make tempura batter
  • Add the chilled flour in 3 additions and mix with chopsticks, drawing crosses and cutting through the batter. Do not use a whisk here and stop while there are still small lumps of flour. Stir in 2 ice cubes to keep it extra cold.
    egg, water and flour in a bowl, drawing crosses in the mixture with chopsticks to make tempura batter
  • Pat the sweet potato thoroughly dry with paper towels. Dust it thinly with cake flour and knock off the excess.
    three slices of soaked Japanese sweet potato dried with a white tea towel
  • Dip each piece into the batter and coat it all over with no gaps, then lower it straight into the oil.
    A slice of Japanese sweet potato coated in tempura batter
  • Fry thin rounds, diagonal slices and sticks at 165 °C (329 °F) to 170 °C (338 °F) for 4 to 5 minutes, turning once. Fry thick rounds at 160 °C (320 °F) for 10 to 12 minutes turning half way through, then raise the oil to 175 °C (347 °F) to 180 °C (356 °F) for 30 to 60 seconds and lift them out at a light color.
    Japanese sweet potato tempura frying in a pot
    • Lift a thick round out once a bamboo skewer slides through the center. Between batches, return the batter to the refrigerator, turn the heat down, and wait until the oil is back at its set temperature before the next batch goes in.
  • Drain in a single layer on a wire rack. Sprinkle half of the ½ tsp salt over while hot. Move the pieces to a plate while the coating is still crisp and serve the rest of the salt in a small dish. Enjoy!
    Japanese sweet potato tempura draining on a wire rack

Notes

Avoid bleached cake flour: Avoid bleached or chlorinated cake flour as it changes the texture. Also avoid self-rising, whole wheat pastry, and gluten-free blends. For UK/AU readers, plain flour works. See flour guide for details.
When all you have is all-purpose flour: Swap the 75 g cake flour and 15 g cornstarch for 65 g all-purpose flour (plain flour in UK/AU) and 25 g cornstarch. The higher starch share thins the gluten, so a stronger flour still fries light.
Stop mixing while lumps are still there: A batter mixed smooth cannot be undone once it hits the oil. Draw crosses through it with chopsticks and stop while small lumps are scattered through it.
Room temperature potato, cold batter: Straight from the refrigerator, the surface burns before the heat reaches the center. Let the sweet potato come to room temperature before you cut it.
Dust only after the surface is dry: Water left on the potato turns to steam the moment it meets the oil, pushes the coating off from the inside and drops it.
Never let the ice reach the oil: If you put ice in the batter, scoop up batter only. An unmelted cube in hot oil is very dangerous, throwing off a burst of steam and spitting violently.
If orange-fleshed sweet potato is all you can find: It carries more water, so skip the thick rounds. Go for thin rounds or diagonal slices instead and dust every piece properly.
If the center is still firm: Do not raise the oil temperature. Give it more time and do not lift it out until a bamboo skewer slides through the center.