Purple Sweet Potato Loaf

by - August 15, 2017

Japanese Purple Sweet Potato Bread

Japanese Purple Sweet Potato Bread

I made this Japanese Purple Sweet Potato Loaf for my step-daughter when she was back for summer holidays recently.  

I have made her few different breads but this is her favourite and she always requests this particular bread. I used the same recipe of Japanese Purple Sweet Potato Buns I shared sometimes ago.

It is advisable to read the following 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 dough until it just reaches or is slightly below the rim of the pan.

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 Sweet Potato Loaf 


400g bread flour (I used Japan High Gluten Flour)
250g mashed japanese purple sweet potato (about 300 - 350g potato - peeled, sliced, steamed and mashed)
30g brown sugar
1 ½ tsp instant active yeast
1 tsp salt
40g whisked egg (from 1 large egg, whisked and keep the balance for egg wash)
120g - 150g fresh milk
60g butter

Egg wash:  Balance of whisked egg from the above + 1 tsp water
Some sesame seeds for topping (optional)

Utensil:  25cm X 12 cm X 11 cm  loaf pan

  1. Put all ingredients (except butter) into the bowl of stand mixer. Using the dough hook, knead for 5 minutes (Chef Kenwood mixer, speed 2.5) until the dough comes together. Add in butter and continue kneading for another 10 - 12 minutes until the dough comes together, become elastic and reaches window pane stage.  Start with 120g of fresh milk first then slowly add in if the dough is too dry.  
  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. Transfer the dough to a clean floured surface then divide into 2 equal portions. Roll out each dough with a rolling pin into rectangle shape. Roll up like swiss roll until a short log is formed.  Place bun onto the baking pans lined with non-stick baking paper. Let it rise for another 45-60 mins or until double in size.
  5. Preheat oven at 190 C (top and bottom heat) or 170C (fan-forced) for 10 - 15 minutes. 
  6. Brush the dough with egg wash and sprinkle with some sesame seeds on top.
  7. Bake in a preheated oven for about 30 minutes or until golden brown.
  8. Remove bread to cool on rack completely.

  1. Please cut down mashed sweet potato to about 200g - 220g if you find the texture too moist for you.
  2. Add 120g of fresh milk first, then slowly add in the rest if dough is too dry.
  3. If fresh milk is not available, you may use 120g - 150g water + 2 tablespoons (20g) of full cream milk powder.

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  1. Hi,
    Does it matter if i put in all the ingredients including the milk together?

    1. Hi Irene,

      Thank you for dropping by. It is ok to put all the ingredients together. But, please don't put salt and yeast together. Please follow the sequence in Step 1.

      Cheers & happy baking:)

  2. Hi Yeanley,
    Thanks for the info.
    Just curious why salt n yeast cannot put together. I hv tried your sweet corn loaf it turned out very pretty n nice. But nt for this sweet potatoes loaf. Im mt sure wht goes wrong.:-(. The dough didnt rise at all.:-(

    1. Hi Irene,

      From my understanding, the salt will kill the yeast if they contact directly. Sorry to hear that your sweet potatoes loaf not successful. It could be many reasons, yeast expired or too much salt or not warm enough? I normally leave my dough to rise inside the oven (door close and off) with a bowl of hot water beside.

      I hope it helps.


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  4. Hi Yeanley,

    Thanks for yr advise, i will try making one more time. Hope this round it is successful.:-)

    Have a nice week end!

    1. Thank you, Irene.. Good luck and let me know ya..

  5. Hi Yeanley,

    May i know what type of butter and milk (low fat/full cream)you used?

    1. Hi there,

      Sorry for late response. I used Lurpak butter and full cream milk or fresh milk.

      Cheers :)

  6. Hi Yeanley

    May i know what type of butter and milk(full cream/low fat) you used?

  7. Can i use 450g loaf tin for this recipe?

    1. Hi, I afraid the bread will over flow. I have not tried this recipe in 450g loaf pan. You may want to try reduce the flour to 320g and reduce the rest of ingredients accordingly by multiply 0.8.
      I hope it helps.
      Cheers :)

  8. May i know where you bought your loaf pan for this recipe?

    1. Hi, thank you for asking. I got this pan from "Bake with Yen" in KL many years ago. But it is not a non-stick pan.
      Cheers :)

  9. Hi Yeanley,
    I cooked purple potatoes in microwave for 10 mins instead of steaming as you said. As the result the dough was far too dry and I ended up doubling the milk in the recipe. So it took me over 15 mins to get the window pane stage. I used 450 g loaf tin and had leftover for a few rolls. They came out beautifully so soft and fluffy, a bit sweet with fragrance.
    Thank you for the lovely recipe. Next time I won’t be too lazy to steam the potatoes.

    1. Hi, thank you for trying this recipe and your kind feedback. Yes, steaming method will yield more moist potato. Happy to hear that you like the bread. Hope will hear from you for your next baking.
      Cheers and happy baking :)

  10. The recipe turned out great. Fragrant bread, and my kitchen smelled like a HK bakery. Only a bit too sweet for my family, so in future I might try with %50 less sugar. Thank you!

    1. Hi, thanks for trying this recipe and your feedback. Yes, please cut down the sugar if it is too sweet for you.

      You are most welcome and happy baking :)