Koji-Fermented Sweet Potato Bread with Black Sesame Recipe
Airy, umami-rich bread with sweetly earthy fermented purple sweet potatoes and a nutty black sesame swirl that balances savory depth with subtle sweetness.
Ingredients
<ul class="ingredients-main-list"><li class="ingredients-single-item">For the Koji Fermentation:</li><li class="ingredients-single-item">300g purple sweet potatoes (or orange sweet potatoes)</li><li class="ingredients-single-item">50g koji rice (or shio koji paste)</li><li class="ingredients-single-item">For the Bread Dough:</li><li class="ingredients-single-item">400g bread flour</li><li class="ingredients-single-item">7g instant dry yeast</li><li class="ingredients-single-item">10g salt</li><li class="ingredients-single-item">30g honey</li><li class="ingredients-single-item">200g koji-fermented sweet potato</li><li class="ingredients-single-item">120ml warm water</li><li class="ingredients-single-item">30g unsalted butter, softened</li><li class="ingredients-single-item">For the Black Sesame Filling:</li><li class="ingredients-single-item">50g black sesame seeds, toasted</li><li class="ingredients-single-item">25g unsalted butter, melted</li><li class="ingredients-single-item">20g brown sugar</li><li class="ingredients-single-item">5g salt</li><li class="ingredients-single-item">For the Topping:</li><li class="ingredients-single-item">1 egg, beaten (for egg wash)</li><li class="ingredients-single-item">10g black sesame seeds</li></ul>
Equipment
<ul class="equipment-main-list"><li class="equipment-single-item">Stand mixer with dough hook</li><li class="equipment-single-item">Digital kitchen scale</li><li class="equipment-single-item">Food processor or spice grinder</li><li class="equipment-single-item">900g (2lb) loaf pan</li><li class="equipment-single-item">Bench scraper</li><li class="equipment-single-item">Fermentation container with lid</li></ul>
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Directions
<ol class="no-list-style"><li class="MethodStepper"><h4 class="step-title">Step 1</h4>Begin the koji fermentation 24-48 hours before baking. Wash and peel the sweet potatoes, then cut into 2cm cubes. Steam until completely tender, about 15-20 minutes. Mash thoroughly while still warm and allow to cool to room temperature. The warm sweet potatoes will help initiate the fermentation process more effectively.</li><li class="MethodStepper"><h4 class="step-title">Step 2</h4>If using koji rice, grind it in a food processor until it becomes a fine powder. Mix the mashed sweet potatoes with the koji rice (or shio koji paste) in a clean fermentation container. Cover and leave at room temperature (20-24°C) for 24-48 hours. The mixture will develop a sweet, fruity aroma with complex umami notes. This fermentation process breaks down starches into simpler sugars and creates glutamates that enhance flavor.</li><li class="MethodStepper"><h4 class="step-title">Step 3</h4>For the black sesame filling, toast the sesame seeds in a dry pan over medium heat until fragrant, about 3-4 minutes. Be careful not to burn them. Grind the toasted seeds in a food processor or spice grinder until they release their oils and form a coarse paste. Mix with melted butter, brown sugar, and salt. Set aside. Toasting develops the nutty flavors while grinding releases the essential oils that carry the sesame flavor.</li><li class="MethodStepper"><h4 class="step-title">Step 4</h4>For the bread dough, combine bread flour, instant yeast, and salt in the bowl of a stand mixer. In a separate bowl, mix 200g of your fermented sweet potato mixture with warm water and honey until smooth. The enzymes from the koji fermentation will help to strengthen the gluten network and improve the bread's texture.</li><li class="MethodStepper"><h4 class="step-title">Step 5</h4>Add the sweet potato mixture to the dry ingredients and mix with a dough hook on low speed until combined. Increase to medium speed and knead for 5 minutes until the dough begins to come together. Add the softened butter in small pieces while the mixer is running. Continue kneading for another 8-10 minutes until the dough is smooth, elastic, and passes the window pane test (when stretched, it should be translucent without tearing).</li><li class="MethodStepper"><h4 class="step-title">Step 6</h4>Place the dough in a lightly oiled bowl, cover with plastic wrap or a damp cloth, and let rise in a warm place until doubled in size, about 1-1.5 hours. The fermented sweet potato will accelerate the rise due to its already active enzymes.</li><li class="MethodStepper"><h4 class="step-title">Step 7</h4>Once doubled, gently deflate the dough and turn out onto a lightly floured surface. Roll into a rectangle approximately 30cm x 20cm. Spread the black sesame filling evenly over the surface, leaving a 2cm border along one long edge. The contrast between the purple dough and black filling will create a stunning visual effect.</li><li class="MethodStepper"><h4 class="step-title">Step 8</h4>Starting from the long edge with filling to the edge, roll the dough tightly into a log. Seal the seam by pinching it firmly. Use a sharp knife or bench scraper to cut the log lengthwise down the center, exposing the layers. Twist the two halves together with the cut sides facing outward, creating a dramatic swirl pattern.</li><li class="MethodStepper"><h4 class="step-title">Step 9</h4>Carefully transfer the twisted dough to a parchment-lined loaf pan. Cover loosely and let rise for another 45-60 minutes until puffy and nearly doubled. Meanwhile, preheat your oven to 180°C (350°F).</li><li class="MethodStepper"><h4 class="step-title">Step 10</h4>Brush the top of the loaf gently with beaten egg and sprinkle with black sesame seeds. Bake for 40-45 minutes until deeply golden and the internal temperature reaches 90°C (195°F). If the top browns too quickly, cover loosely with foil after 25-30 minutes. The egg wash will give your loaf a beautiful shine while helping the sesame seeds adhere.</li><li class="MethodStepper"><h4 class="step-title">Step 11</h4>Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing. This resting period allows the crumb structure to set properly. The bread will showcase a beautiful purple hue with striking black sesame swirls throughout. Enjoy this unique bread with a subtle sweetness, complex umami notes, and nutty sesame flavor!</li></ol>
Chef’s Notes
A few helpful details for making this recipe.
What is koji and why is it used in bread making?
Koji is a traditional Japanese culture made by growing Aspergillus oryzae mould on grains like rice. In bread making, it introduces enzymes that break down starches into sugars, creating complex umami flavours and improving texture. It naturally enhances sweetness, extends shelf life, and adds remarkable depth to baked goods.
Can I use regular sweet potatoes instead of purple ones for this fermented bread?
Yes, orange or yellow sweet potatoes work perfectly in this recipe - you'll simply lose the striking purple colour. The fermentation process will still develop the same depth of flavour and enhance the natural sweetness regardless of which variety you choose. The texture and umami qualities remain comparable.
How long will this fermented sweet potato bread stay fresh?
Thanks to the koji fermentation, this bread stays fresh longer than typical homemade loaves - about 4-5 days at room temperature in an airtight container. It also freezes exceptionally well for up to 3 months. The fermentation process improves shelf life by altering starch structures and pH levels.
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