Purple Sweet Potato Buns (Old Dough Method)

by - July 17, 2017

Japanese Purple Sweet Potato Buns

Japanese Purple Sweet Potato Buns

Japanese Purple Sweet Potato Buns

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. 

Please scroll down to see the Straight Dough Method Recipe.   You may also find the natural yeast recipe here "Purple Sweet Potato Soft Sourdough Bread"

It is advisable to read the below general notes before starting baking.


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.

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.

Recipe -  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 (about 250g potato - peeled, sliced, steamed and mashed)
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

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 milk/water, yeast and sugar in a mixing bowl.  Then add in bread flour and knead with your hand until smooth and all incorporated.  Roll into a ball and place in a greased bowl.  Cover with cling film and let it ferment for 12 - 16 hours in cool place or  air-conditioned room (25C - 26C) if you live in a hot climate.
    2. You may also let it proof 1 hour in room temperature (hot climate). After 1 hour, place into the refrigerator for 24 - 36 hours.  Take out the old dough from refrigerator to return to room temperature 30 minutes before using
  2. 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.
    2. 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.
  3. 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.
  4. 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.


Japanese Purple Sweet Potato Bun

Japanese Purple Sweet Potato Bun

This Japanese Purple Sweet Potato Bun recipe yields soft and cottony buns that you can eat plain. If you are looking for soft and fluffy buns, this is the recipe for you.  In order to get this nice vibrant purple colour, please use the Japanese Purple Sweet Potato instead of local Purple Sweet Potato.  

You may also like my other Purple Sweet Potato Bread recipe.

Recipe - Purple Seeet Potato Buns (Straight Dough Method)

Yields:  16 buns


400g bread flour
250g mashed japanese purple sweet potato (about 300 - 350g potato - peeled, sliced, steamed and mashed)
1 ½ tsp instant active yeast
30g brown sugar
1 tsp salt
40g whisked egg (from 1 large egg.  Balance to be used for egg wash)
60g butter
120g - 150g fresh milk

Egg wash - 10g whisked egg + 1 tsp water
2 tbsp sesame seeds for topping

10 inches square pan

  1. Put all ingredients (first add salt, flour, sugar, yeast, butter, egg, mashed potato and lastly fresh milk) in a bowl of stand mixer and knead till the dough come together, until achieve window pane stage (the dough at this stage should be able to be pulled and stretched into membrane).  It takes around 10 to 15 minutes at medium speed.  If the dough is wet, add 1 tablespoon of flour at a time until you get the consistency you want.
  2. Form the dough into a round ball and let it rise in a warm place for 1 hour or until double in size in a large greased bowl, covered with cling film or kitchen towel.  I normally leave the dough in the stand mixer’s bowl and cover with kitchen towel.
  3. Punch down the bread dough to release the air.
  4. Divide dough into 12 equal portions and shape into balls. Place bun onto the baking pans lined with non-stick baking paper. Let buns rise for another 45-60 mins or until double in size.
  5. Brush the buns with egg white/water mixture and sprinkle with some sesame seeds on top.
  6. Preheat the oven at 190C (top and bottom heat) or 170 (fan-forced mode) for 10 minutes.
  7. Bake at a pre-heated oven for 15 - 20 minutes.
  8. Remove buns to cool on rack completely.
  1. Add 120g of fresh milk first, then slowly add in the rest if dough is too dry.
  2. If fresh milk is not available, you may use 120g - 150g water + 2 tablespoons (20g) of full cream milk powder.
  3. Please cut down the mashed potato to about 200g - 220g if you find the texture is too moist for you.

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  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 taste..do 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: https://www.bakewithpaws.com/2020/09/japanese-soft-white-buns.html

      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 :)