Apologies for the long post, but if you stay to the end, there's a magic trick for the kid in you!
I was so so excited to see stokes organic purple sweet potatoes sold at my nearby Costco, and so grabbed a whole 3 lb bag.
This purple sweet potato is different from the Okinawan sweet potatoes that I used to make my baked mochi in hawaii. Here, the skin and flesh are both purple, whereas the skin of the Okinawan sweet potato is white, while the flesh is a deep blue purple. Also, the flesh of the stokes purple sweet potato is less starchy and more fibrous compared to the Okinawan sweet potato. Taste-wise tough, they are both mildly sweet and delicious simply steamed until soft.
But with the beautiful purple flesh, I wanted to make some fluffy steamed purple lotus leaf buns--cuz they'd be so pretty and healthy!
I figured that I could just replace a portion of the flour with mashed sweet potatoes in the recipe for lotus leaf buns by the woksoflife.com, one of my favorite websites for Chinese recipes. The recipe looked easy enough, especially if I took the short cut of throwing everything in the bread maker to assist with the mixing, kneading and rising.
I did find it interesting that the recipe called for adding BOTH yeast and baking soda, but I looked up a couple of other recipes for Chinese steamed buns (mantou), including the original Momofuku lotus leaf bun recipe, and they also added baking soda, so I went with it.
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| Steam |
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| Peel and discard skin |
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| Mash |
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| Add all ingredients to bread maker |
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| Used Bread Maker dough setting (1 hr 45 min): It mixes, kneads and rises for you |
Look at the beautiful purple color of the pillowy dough!
I had a lot of fun shaping the dough. Round buns, flowery buns, lotus leaf buns. Whatever shape you want!
After shaping and resting again, I placed them in the steamer. After 12 minutes of steaming, this is what happened.
The color changed to a bluish green color! NOooooo...
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| After steaming, it's NOT Purple!!! |
The taste and fluffy texture with a slight chew was there, but it was just NOT the color I was going after.
So I thought about it some more and realized that the purple color in the sweet potato comes from naturally occurring anthocyanins in the tubular. And depending on the pH (acidic, neutral, or basic), anthocyanins can display a range of colors from red pink (acidic, pH <7) to purple (neutral, pH = 7) to greenish black (basic, pH >7). So the baking soda (sodium bicarbonate, which is basic) caused my buns to turn bluish green. Normal yeast breads without sodium bicarbonate are slightly acidic, and hence would have stayed purple. Read all about anthocyanins here!
So I repeated the recipe, but omitted the baking soda. The starting raw dough was a bit more of a reddish purple this time. So far so good.
As it was getting super late into the evening, no fancy shapes. I just rolled them into balls and plopped them into cupcake liners.
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| BATCH 2: No Baking soda |
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| BATCH 2: No Baking soda |
After steaming, it was less vibrant, but was still purple.
Hooray!
Without the baking soda, the buns came out kind of lumpy instead of smooth. A bit ugly, for sure, and definitely not presentable to company, but the taste and texture are still good.
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| Batch 2: No Baking soda |
You can serve these buns by slicing them open and tucking in some kalua pork and pickled daikon and carrots, or with duck and hoisin sauce, or BBQ pulled pork and pickles.
Now for the magic trick I promised!
If you make the buns that are blue green in color, and serve them with anything pickled (pickled daikon and carrots, pickled cabbage, jarred pickles, etc), the pickles that touch the buns will turn purple! That's the anthocyanins going from a basic environment to an acidic one. The kids (or the kid in you!) will have a blast, especially if they are just studying pH in school!
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| Green blue bao cut open |
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| Add pickles or anything acidic |
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| Where acid meets, bao turns purple. MAGIC! |
Here's the recipe below for the bao buns adapted from Woks of Life lotus leaf buns recipe.
Yields 12 buns
Ingredients:
- 1 c mashed purple sweet potato (about 0.5 lb, 1 to 2 small sweet potatoes*)
- 2 c all purpose flour
- 2 T sugar
- 1 t yeast
- 2/3 c water
- 2 T olive oil
- ½ t baking soda (leave out if you want purple buns. Put in if you want green blue buns)
- ¼ t salt (leave out if you want purple buns. Put in if you want green blue buns)
* In the pictures, I show steaming and mashing 3 sweet potatoes. That was about 1 lb of sweet potatoes and yielded 2 cups mashed. This recipe is scaled to use only 1 cup of mash.
Procedures:
1. Steam the purple sweet potatoes until fork tender (about 30 minutes).
2. Remove and discard the skin of the sweet potatoes. Mash the flesh of the sweet potatoes with a spoon and measure out 1 cup of mash.
3. If you have a bread maker, add all the ingredients to the bread maker and set it to the dough setting so that the bread maker will mix, knead, and rise the dough for you. If you don’t have a bread maker, then mix all the ingredients together in a bowl until combined. Then knead the dough for 15 minutes until smooth. Cover the dough with a damp cloth and allow it to rise for 45 minutes, or until approximately double in size.
4. After the dough is done rising, place the dough on a lightly floured surface and divide the dough into 12 equal pieces.
5. Shape the dough to whatever your heart desires. You can just roll it into a round ball and place it onto a cupcake liner. Or you can flatten the dough to a thin ¼ inch disc, brush some oil on one side, and fold it in half such that the oiled half is on the inside to make a lotus leaf shape and place it onto a cupcake liner. Or you can flatten the dough to a thin oval, slice one end into 4 strips, grab both ends and twist connecting both ends to make a flower and place it onto a cupcake liner. (See photos)
6. Cover the formed buns with a clean cloth and allow them to rest for 15 minutes.
7. Steam the buns for 12 minutes. When the 12 minutes are up, turn off the heat and crack the lid of the steamer open, being careful not to let any water drip onto the buns. Allow the buns to set for 3 minutes in the steamer, then remove from the steamer and enjoy hot or at room temperature.