Purple Sweet Potato Sourdough

Ingredients

The Dough

This is a lean sourdough, not enriched. No butter, no eggs. The sweetness and moisture come entirely from the sweet potato.

• 405g (3¼ cups) bread flour 90% — 12-13% protein preferred
• 45g (6 tbsp) whole wheat flour 10%
• 290g (1¼ cups) water 64% — Room temperature (75°F / 24°C)
• 90g (6 tbsp) active sourdough starter 20% — At peak activity
• 150g puree OR 30g powder (½ cup puree OR 3 tbsp powder) purple sweet potato puree or powder — Puree contributes ~105g moisture. If using powder, add 30g extra water.
• 9g (1½ tsp) fine sea salt 2%

For the Loaf Pan Version (optional additions)

If making the sandwich loaf version, these small additions make the crumb softer and more sliceable.

• 15g (1 tbsp) honey
• 20g (1½ tbsp) olive oil

Equipment

• Dutch Oven
• Banneton Proofing Basket
• 9x5 Inch Loaf Pan (optional)
• Baking Scale
• Bench Scraper
• Lame or Sharp Razor Blade
• Instant Read Thermometer

Method

Prepare the Sweet Potato

This step takes 20-30 minutes and can be done the night before. The puree needs to be fully cooled before it goes into the dough.

1. Cook the potato. Scrub one medium purple sweet potato (about 200g whole). Steam for 20-25 minutes until completely tender when pierced. Steaming gives the most vivid color because boiling leaches the anthocyanins into the cooking water.
2. Peel and mash. Once cool enough to handle, peel and mash thoroughly until completely smooth. No lumps. Use a fork, potato ricer, or immersion blender. Weigh out 150g of puree.
3. Cool completely. The puree must be at room temperature or cooler before going into the dough. Hot puree kills starter. Spread it on a plate to cool faster, or refrigerate it overnight.

Tip: Can't find fresh purple sweet potatoes? Ube (purple yam) works beautifully and is more widely available at Asian grocery stores. If using powder, brands like Suncore Foods are available online.

Verify Your Starter

This is a lean dough so fermentation moves predictably, but starter health still matters.

1. Float test. Drop a small spoonful of levain into a glass of water. If it floats or hovers, it's ready. If it sinks, give it another 1-2 hours.
2. Visual check. Your starter should be domed or just starting to fall, with bubbles visible throughout. It should smell active and tangy, not flat.

Mix and Autolyse

The autolyse gives the flour time to fully hydrate before we add the starter and salt. With the sweet potato in the mix, this rest period also allows the color to start distributing through the dough.

1. Combine flours and water. In a large bowl, combine the bread flour and whole wheat flour. Add the water and mix with your hands until no dry flour remains. The dough will look rough and shaggy.
2. Add the sweet potato puree. Add the cooled purple sweet potato puree (or whisk the powder into the water before adding flour if using powder). Mix until incorporated throughout. The dough will turn a striking purple-grey at this stage.
3. Cover and rest. Cover the bowl with a damp towel or plastic wrap and let rest for 45-60 minutes at room temperature.

Wait: Autolyse Rest

Add Starter and Salt

After the autolyse, the dough is more extensible and receptive to the starter. Adding salt at this stage gives the gluten a head start before the salt tightens it.

1. Add starter. Add the active levain to the autolysed dough. Use your fingers to squish and fold it in until fully incorporated, about 3-4 minutes of firm hand mixing.
2. Add salt. Sprinkle the salt evenly across the dough. Fold and squeeze to incorporate fully. Give it 2-3 minutes of active mixing.
3. Loaf pan option: add honey and oil. If making the sandwich loaf version, add the honey and olive oil now. Skip this step if making the artisan boule.
4. Rest 30 minutes. Cover and rest for 30 minutes before beginning the stretch and fold series.

Bulk Fermentation

This is a lean dough so it behaves like a standard sourdough. Look for roughly 75-80% rise and a dough that feels noticeably lighter and more airy.

1. First set of stretch and folds. At 30 minutes, perform one set of stretch and fold. Wet your hand, grab one side, stretch up, fold over. Rotate 90 degrees and repeat. Four folds equals one set.
2. Second and third sets. Repeat a set of stretch and folds at 60 minutes and again at 90 minutes. After the third set, the dough should feel noticeably smoother and the purple color will be deepening.
3. Optional lamination for deeper color distribution. After the third stretch and fold set, you can do one lamination pass instead of a fourth fold. Wet your work surface, stretch the dough into a thin rectangle, fold in thirds like a letter, then fold in thirds again. This distributes the color and adds significant dough strength.
4. Rest undisturbed. After all folds, let the dough rest undisturbed until bulk fermentation is done. Total bulk time at 75-78°F (24-26°C) is approximately 5-8 hours from when you added the starter. Watch the dough, not the clock.

Wait: Bulk Fermentation

Preshape and Bench Rest

A good preshape builds surface tension that gives you oven spring and a clean score line.

1. Preshape. Turn the dough onto a lightly floured surface. Using a bench scraper and your free hand, shape into a rough ball by folding the edges under and dragging it toward you to build tension. Don't deflate it.
2. Bench rest. Leave the preshaped dough uncovered on the counter for 20-30 minutes. It will relax and spread slightly.

Wait: Bench Rest

Final Shape and Cold Proof

Shape with confidence. The cold retard overnight gives this loaf its ear and bloom when baked.

1. Final shape for boule. Fold the dough in thirds, flip it over and use the bench scraper and your palm to drag it toward you, building a tight skin on the outside. Place seam side up in a well-floured banneton. Dust with rice flour.
2. Final shape for loaf pan. For a sandwich loaf: pat the dough gently into a rough rectangle. Fold the long sides to center, then roll from the short end into a tight log. Place seam side down in a greased 9x5 inch loaf pan.
3. Cold proof overnight. Cover the banneton with a clean shower cap or plastic bag. Refrigerate for 10-14 hours.

Tip: Rice flour in the banneton is not optional. All-purpose flour can absorb moisture and cause the dough to stick and tear.

Bake

Bake straight from the refrigerator. Cold dough holds its shape better when you scoring it.

1. Preheat with Dutch oven. Place your Dutch oven (lid on) in the oven and preheat to 500°F (260°C) for at least 45-60 minutes.
2. Score the dough. Remove the cold dough from the banneton onto parchment paper. Score quickly and confidently with a lame or razor blade at a 30-45 degree angle. One clean ear cut works perfectly.
3. Bake covered. Carefully lower the dough on the parchment into the hot Dutch oven. Lid on. Bake at 500°F (260°C) for 20 minutes.
4. Bake uncovered. Remove the lid and reduce to 450°F (232°C). Bake for an additional 20-25 minutes until the internal temperature reads 205-210°F (96-99°C).
5. Cool completely. Remove the loaf and cool on a wire rack for a minimum of 2 hours before cutting. The sweet potato starch holds moisture. Cutting early results in a gummy interior.

Shape for the Reveal

Your shaping choice determines what the final loaf looks like. The boule gives you the dramatic crumb shot. The loaf pan gives you clean slices for everyday eating.

1. Choose your shape. Boule: fold in thirds, flip, drag with bench scraper. Loaf: pat to rectangle, fold sides in, roll from short end.

Bake with Steam

High heat, trapped steam, then an uncovered finish.

Oven: 260°C / 500°F. Internal temperature when done: 96°C / 205°F.

Bake time: PT45M

Equipment: Dutch oven with lid, parchment paper

1. Preheat with Dutch oven inside for 45-60 minutes minimum.

Storage

• Room temperature: 3-5 days. Purple sweet potato breads stale very slowly due to the potato starch. Store cut side down on a wooden board or in a bread bag.
• Refrigerated: Not recommended, causes staling
• Frozen: Up to 3 months. Slice before freezing. The color holds well.
• Refresh: Toast slices directly from frozen or warm at 350°F (175°C) for 10-12 minutes.

Frequently Asked Questions

Where do I find purple sweet potatoes?

Look for Stokes Purple or Japanese purple sweet potatoes at Asian grocery stores, Whole Foods, or specialty produce markets. They're most widely available September through April. Ube (purple yam) works as a substitute. Purple sweet potato powder from brands like Suncore Foods is available online year-round.

My dough turned grey or brownish instead of purple. What happened?

This is usually caused by oxidation. Anthocyanins are sensitive to air exposure and will shift from purple toward blue-grey over time. Some color shift during fermentation is normal. The baked interior almost always retains more vivid color than the pre-baked dough.

The crumb is more pink than purple. Did I do something wrong?

Anthocyanins are pH-sensitive. In an acidic environment (which sourdough is), they shift from purple toward pink and red. The more sour your loaf, the more pink the crumb. A milder starter will retain more blue-purple.

Can I use this recipe with yeast instead of sourdough?

Yes. Replace the 90g of starter with 7g of instant yeast (about 2 teaspoons). Reduce the water by about 45g. Bulk fermentation drops to 1-1.5 hours. Everything else stays the same. The color will be identical.

My loaf came out gummy in the center even though it was fully baked.

This is the most common issue with sweet potato breads and it's almost always caused by cutting too soon. The starch from the sweet potato holds moisture and needs the full 2-hour cooling period to set. Give it the full cool.

Can I add mix-ins like walnuts or cranberries?

Absolutely. Add 80-100g toasted walnuts or 60-80g dried cranberries during the lamination pass in bulk fermentation, about 2 hours in. Scatter across the stretched dough before folding.

Nutrition

Per serving (1 slice (75g)): 185 calories, 37g carbohydrates, 6g protein, 1g fat, 2g fiber, 230mg sodium.