Breads (Yeast) - Buns/Rolls

Purple Sweet Potato Buns

July 17, 2017 | Recipe by Bake with Paws
Japanese Purple Sweet Potato Buns

Japanese Purple Sweet Potato Buns

Japanese Purple Sweet Potato Buns

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I have been baking this Purple Sweet Potato Buns since I started baking few years ago.  And it is still as one of my favourite.  I started with baking straight dough method.  A lot of people tried this recipe and they like it too.  

I have also been asked by many whether this recipe can be converted to Yudane Method.  I don't encourage using Yudane Method for sweet potato bread it is because it will make the texture too moist. Potato starch also absorbs more water than wheat starch and this makes the bread texture more moist and have better shelf live. So, it does not need yudane dough.  However, I think old dough method will work better.  So, I decided to try and the texture is really soft and fine.    From my experiment, old dough method yields more fine texture compared with straight dough method for this bread.

I used pâte fermentée (pre-fermented dough in French) or sometimes called "old dough" to make this fine, soft and flavourful bread.  Traditionally, bread makers take a portion of the bread dough made and save it overnight for next day baking.  I made it from scratch since I did not have any ready old dough. With this method, the bread is more flavourful and aromatic due to the higher acidity and fermentation gasses produced during the slow fermentation.

Please click on Bread Making Method to understand more details. 

You may also find the natural yeast recipe here "Purple Sweet Potato Soft Sourdough Bread"

If you have any questions regarding this recipe or any other post, please leave me a comment in the “LEAVE A COMMENT” link and I will reply you as soon as possible.  Do tag me on Instagram @Bakewithpaws if you attempt on this.

How To Make  Purple Sweet Potato Buns (Old Dough Method)

Yields: 9 Buns


Old Dough:
175g bread flour (I used Japan High Gluten Flour)
115g full cream milk (whole milk) or fresh milk or water
1/4 tsp instant yeast
1/4 tsp sugar

Main Dough:
175g bread flour (I used Japan High Gluten Flour)
200g mashed japanese purple sweet potato (2 potatoes about 250g)
All the old dough (above)
2 tbsp (24g) brown sugar
1/2 tsp instant yeast
1 tsp salt
45g egg, whisked 
10 - 20g milk (reserve 10g first and add in later if needed)
50g butter, room temperature

Egg Wash:
1 egg + 1 tbsp water 

8 inches square pan,  lined with parchment paper.  You can also bake this into a loaf in 450g loaf pan.

  1. Old Dough
    1. Combine water, yeast and sugar in a mixing bowl. Then mix with hand. Roll into a ball and place in a greased bowl.  Cover with cling film and let it proof 1 hour in room temperature (28C).  After 1 hour, place into the refrigerator overnight for at least 12 hours or up to 36 hours.  The next morning, take out the old dough from refrigerator to return to room temperature 30 minutes before using.
    2. You can also let it ferment for 12 - 16 hours in cool place or  air-conditioned room (22C - 23C)
  2. Mashed Purple Sweet Potato:
    1. Wash, peel and cut the potato.  
    2. Steam for 15 minutes or until potatoes are soft.
    3. Mash the potato with a potato ricer or masher.  Set aside to cool.
  3. Kneading Main Dough:
    1. Put all ingredients (except butter) including all the old dough into a bowl of stand mixer. Using the paddle attachment, mix for 2 minutes or until all incorporated. Please add 1 tablespoon of milk/water if the dough is slightly hard and dry.  Change to hook attachment and knead for another 3 minutes or until the dough comes together. Add in butter and continue knead for 10 - 12 minutes or until reach window pane stage. During the whole kneading process, I stopped few times to scrape down the dough from the hook to be sure it is evenly kneaded and also to prevent the motor from overheating.
  4. 1st Proofing:
    1. Let the dough rise in a warm place for 45 to 60 minutes or until double in size in a large greased bowl, covered with cling film or kitchen towel.
  5. To shape:
    1. Punch down the dough to release the air.  Transfer the dough to a clean floured surface then divide into 9 equal portions. 
    2. Form each portion to a ball.  Please watch the video "How to shape the Buns"
    3. Place all dough balls in a prepared baking pan.
    4. Let the dough rise for 30 - 45 minutes or till about 90% of the size.
  6. To bake:
    1. Preheat the oven at 190C (top and bottom heat) or 170 (fan-forced mode) for 10 minutes.
    2. Brush with egg wash.
    3. Bake at preheated oven for about 15 - 20 minutes, or until golden brown.
    4. Remove buns from oven and the pan, let the buns cool on rack.


For kneading, please regard the timing provided as an indication only. It is only meant as a guide.  Timing may differ depending on the brand of flour and electric mixer used. The protein content may vary from one brand of flour to another.

Some have experienced the dough breaking during the second proofing.  If that happens it is due to over kneading.  Please stop the machine and check your dough during the final cycle of kneading to ensure that you don't over knead. Every machine is different and there is always a chance of over-kneading when using a machine. You may need to adjust this timing and stop as soon as you reach the window pane stage.

The right flour plays a very important role in bread making.  Usually bread flour content around 11.5 - 13.5% protein, while high gluten flour is around 13.5 - 14.5%.  All purpose flour content less protein around 9 - 11%.  To achieve fluffy, soft and light bread, I used Japan High Gluten Flour in most of my bread baking.  Sources from here and here.

The liquid measurement given is also a guide.  It is advisable to always reserve some liquid and not add it all in one go.  This would give you the opportunity to adjust if necessary. If dough is too dry, add the reserve liquid one tablespoon at a time until the right consistency.  This is because each flour absorbs water and hydrates differently. 

Please note that the proofing timing may also vary depending on your climate and environment. The humidity and temperature at your place will influence how dough rises.  If you are unable to judge by just looking at the dough, you can do the finger poke test:
  1. First Proofing:
    • Lightly flour or oil your finger or knuckle, gently poke in the centre of the dough then remove your finger.  If it bounces back immediately without any indentation then it needs more time.
    • If the indentation stays and it doesn’t bounce back or if the dough collapses, then the it is over proved.  
    • If it bounces back just a little, then the dough is ready to be punched down and shaping.
  2. Second Proofing:
    • Lightly press the side of the proved dough with your finger.  If it bounces back immediately without any indentation, it means the dough is under proved and needs more time before baking.
    • If the indentation stays and it doesn’t bounce back, it means it has been over proved.
    • If the indentation slowly bounces back and leave a small indentation, it is ready to bake. 
    • There will be a final burst of rising once the bread is placed to bake in the oven and it is called oven spring. 
If your bread collapses or gets wrinkled on top after removing from oven, it could be because your dough over proved during the second proofing. Please proof your buns until 90% of the size.

Do also note that the baking temperature and timing provided are what works for my oven and should also be regarded as a guide only. Every oven behaves a little differently, so please adjust accordingly for your oven.


  1. This is super awesome! Ive baked it and gonna bake more and more. Tq for the great recipe!

    1. Hi there,

      Thank you for trying this recipe and your feedback. I am happy to hear that you like it.

      Cheers :)

  2. Rats! Mine had a bitter you know why it might have turned out like this for me?

  3. Rats! My buns turned out bitter for some reason. Do you know what I might have done wrong? Or did I just have bad sweet potatoes?

    1. Hi, Thank you for trying this recipe. Sorry to hear that your buns turned out bitter. It must be the sweet potatoes potato. There is no other reasons that can make your bread bitter. I have accidentally eaten bad sweet potatoes before, the taste is bitter.

      Cheers :)

  4. May I know if I could omit the sweet potato for the plain bun version? Thanks !

    1. Hi, Thanks for reading this recipe. You need to adjust some of the ingredients. It is better for you to use the following recipes:

      Japanese Soft White Buns:

      Pull-apart buns:

      I have other old dough method recipes. Please search under old dough method.

      Cheers :)

  5. Hi YL, for this recipe, Purple Sweet Potato Buns (Old Dough Method) using 450g covered loaf pan, what is the temperature and how long to bake?

    1. Hi Janice,

      Around 180C - 200C for about 30 minutes.

      Cheers :)

  6. Hi, may I substitute instant yeast with active yeast ?

    1. Hi, thanks for visiting this recipe. Yes, you can. But, I am not sure how. Please google search.

      Cheers :)


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