Japanese Purple Sweet Potato Bun

by - July 17, 2017

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.

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 - Japanese Purple Seeet Potato Buns

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. Bake at pre-heated oven at 170C - 180C for 25 to 30mins.
  7. 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 :)