The steamed cha siu (Chinese BBQ pork) bao has been my nemesis for quite some time. It all started with my dad's requests for homemade steamed cha siu bao. I had successfully made steamed buns in the past, so I thought "How hard could steamed cha siu bao be?" Many failures later, I learned the answer was, "Pretty hard." My baos were never fluffy enough and they didn't have the signature "cracked" look. And they didn't pass my dad's taste test. Ugh.

During my work sabbatical (thanks HubSpot!), I decided to revisit the cha siu bao challenge. As I researched different recipes, I came across a recipe on YouTube by Chinese Cooking Demystified that used a sourdough starter to create the bao. I was intrigued. Like many, I had delved into the world of sourdough during the pandemic and had come to like my new little refrigerator pet.

I invested 4-5 days in testing out this recipe, creating a new starter from scratch, and had high hopes for these baos. However, my results were ruined by one of the other key ingredients in the recipe -- ammonium bicarbonate. Ammonium bicarbonate is a strong leavening agent ("baking soda on steroids") with an equally strong smell. The smell was supposed to dissipate after some resting time, but mine lingered in my bao, rendering them inedible.

I was a little defeated, but the idea of using a sourdough starter still intrigued me. I searched around the internet for alternative cha siu bao recipes that used sourdough starters, but many still called for ammonium bicarbonate. Finally, during one late night search, I stumbled upon a recipe posted on Facebook by Hui's Food Diary. Not only did it use a 100% hydration starter (commonly what's used in western sourdough breads, although this starter was 50% plain flour + 50% low protein flour), but it also boasted short rest times. It still included ammonium bicarbonate and Kan Sui (alkaline water), but the author wrote about how they forgot the ammonium when making these and they still got good results. It sounded promising, so I gave the recipe a test. 

Because I don't like buying extraneous ingredients, I made a few changes. 

1. I used all purpose flour fed sourdough starters.
   I tested out two types of starter:
   • 100% hydration starter (1:1:1 | starter : water : AP flour)
   • 75% hydration starter (4:3:4? | 100g starter : 75g water : 100g AP flour). I chose to test a 75% hydration starter because I had read that lower hydration starters are used for stiffer baked goods. Perhaps it would help with the structure of the bao? 
2. I used butter instead of lard because that's what I had on hand
3. I added cornstarch as an ingredient. Borrowing inspiration from The Woks of Life recipe, I hoped the added cornstarch would help create a fluffier texture.

10+ experiment runs and 80+ baos later, I think I've settled on a recipe that has worked for me pretty consistently. The baos are fluffy and cracked, and approved by my dad! 

This is my first time testing and altering a recipe, so I would love for people to try it out and provide feedback. Let's dive into it!

the recipe

The starter

After testing, I found that the 75% hydration starter produced fluffier and lighter baos. With the lower hydration, I was able to add less flour to the starter when making the bao, resulting in a less dense bao.

To get a 75% hydration starter, take a small amount of your 100% hydration starter and feed it in a 4:3:4 ratio (100g starter : 75g water : 100g AP flour) for about 2-3 rounds of feeding. Maintain/activate this starter as you would your regular sourdough starter, just with the altered 4:3:4 ratio. 

This recipe requires the starter to be ripe, so if my starter has been in the fridge, I'll do two rounds of feeding. I try to avoid discarding my starter if possible, so I feed it like so:

1. 16 hours ahead: 50g starter + 38g water + 50g AP flour (total weight 138g)
2. 8 hours later: 138g  starter + 104 water + 138g AP flour (total weight 380g)

Usually about 6-8 hours  after the second feeding, my starter will be bubbly and be double to triple the original volume. The recipe calls for 300g of starter, so that'll leave us 80g of starter to keep for next time. 

The filling

The filling consists of two parts -- the cha siu, and the sauce.

Cha siu

While I did roast my own cha siu for my baos, I don't have a recipe for the homemade cha siu prepared for this blog post. You can either buy it from your local Chinese butcher shop, or make it at home following some other recipes. I love using The Woks of Life recipes, so check theirs out!

Sauce

The sauce recipe is from the Chinese Cooking Demystified video, with small modifications. It calls for a flavored oil made from cooking oil with scallions and onions. This provides key flavors to the sauce, don't skip this step!! 

Ingredients

• Cha siu, chopped into small thin pieces*
• Scallion oil
  • 1 cup canola or peanut oil
  • 12 scallion whites, sliced into strips
  • 1/4 sweet or white onion, sliced
• Thickening slurry
  • 1/3 cup water
  • 2 tbsp corn starch
  • 1 tbsp cake flour
• Sauce
  • 1.5 tbsp light soy sauce
  • 1 tsp dark soy sauce
  • 1/2 tsp hoisin or chu hou sauce
  • 1.5 tbsp oyster sauce
  • 3.5 tbsp sugar
  • 1/2 tbsp sesame oil
  • 1/3 cup water
  • 2 tbsp scallion oil (separated into tbsps)
  • thickening slurry (above)

Method

1. Make the scallion oil. Over medium high heat, cook oil, scallion whites, and onion until the oil starts to bubble, then switch to low heat. Cook for ~8 minutes until onions are golden brown. Turn off the heat and strain oil into a jar to keep. 
2. Make the thickening slurry. Combine water, corn starch, and cake flour in a small bowl. Mix until mixture is smooth.
3. Assemble the sauce. In a sauce pan, add soy sauce, dark soy sauce, hoisin/chu hou sauce, oyster sauce, sugar, salt, sesame oil, water, and 1 tbsp scallion oil. Cook on low heat until sugar is dissolved.
4. Thicken the sauce. Give your slurry a stir and then add to the sauce pan. Stir continuously and cook until the sauce is well thickened.
5. Finish the sauce. Once the sauce is thick, turn off the heat and stir in 1 tbsp of scallion oil. Pour sauce into a container and refrigerate for at least 3 hours until completely chilled.
6. Add cha siu. After sauce has cooled, add chopped cha siu and mix it into the sauce. Refrigerate filling until ready for use. 

* I like a ratio of about 1:2 for cha siu : sauce, e.g. 50g cha siu + 100g sauce