Sourdough Frosting

When I first developed this Sourdough Frosting recipe, I figured people might think I was crazy or a genius. And while the thought of adding sourdough to a peculiar, it’s actually phenomenal!

The idea came to me reading about ermine frosting, an old-fashioned boiled milk or cooked flour frosting, that uses less sugar than traditional buttercreams. Since sourdough starter is 50/50 flour and water, I tried it in place of the flour, and was amazed with the outcome.

The sourdough frosting is surprisingly stable like Swiss buttercream (but egg-free), making it perfect for frosting cakes like this sourdough gingerbread cake, cupcakes, or as a flavored filling for pumpkin or chocolate whoopie pies.

The sourdough adds a subtle tang, akin to cream cheese frosting, and has a fluffy and light texture almost like whipped cream. Even better, it has less sugar than other buttercreams without sacrificing on flavor!

I hope I’ve sold you on this sourdough frosting, because it really is a completely unique and remarkable frosting that I’ve never seen before. I’m really proud to bring it to the world and hopefully inspire you to use it in your dessert creations or make one of its many variations listed below.

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👍 Why I Love This Recipe

• Fluffy like whipped cream
  • This versatile sourdough frosting has a texture akin to whipped cream! It’s fluffy, silky smooth, and airy.
• Less sweet than most buttercreams
  • There’s less sugar and butter in sourdough frosting than traditional buttercreams. You can see this handy sugar/butter chart, comparing ermine frosting to other frostings, which this sourdough frosting is derived from.
  • The sourdough adds a subtle tang to the frosting, creating a nuanced balance to the sweetness- making it an ideal complement for red velvet cakes. It’s why cream cheese, sour cream, or yogurt frostings are so good.
• Surprisingly stable
  • Because of the cooked roux mixture, this sourdough frosting is very stable. It handles warmer temperatures and humidity better than American buttercream and works well as a filling, for pipping, or decorating.
• Stores well for up to a week
  • Sourdough frosting stores extremely well up to a week in the refrigerator. You’ll need to bring it to room temperature and re-whip before using.
  • You can also make the sourdough roux in advance for a few days and keep it in the refrigerator.

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🔍 Troubleshooting Tips for Making Sourdough Frosting

• Why did my sourdough frosting curdle?
  • Buttercreams curdle when the ingredients are too cold or not whipped enough. The ideal temperature for the softened butter and frosting is between 65-75ºF.
  • If the frosting curdles, you can set the frosting over a water bath to heat up slightly and re-whip it. You may also need to keep whipping the mixture for longer to warm it up (as long as 10 minutes more).
• Why is my sourdough frosting greasy?
  • A greasy frosting means that the frosting or butter was too warm or it melted. You need to chill the mixture in the refrigerate until it’s more set and then re-whip.
• My frosting is runny
  • You may not have cooked the roux mixture enough, resulting in a runny frosting. The roux mixture should be thickened like pudding or pastry cream.
  • Additionally, if you add the hot roux to the butter, it will melt the butter, resulting in greasy or runny frosting.
• How to make the frosting whiter
  • This sourdough frosting typically comes out very bright white, perfect for decorating birthday cakes. However, the ingredients you use can affect the color of the frosting.
  • Use a pale, unsalted butter (like most name brand butters) and not high-fat butters, such as Kerrygold (save that for croissants or pie crust!). These will make your frosting more yellow.
  • You can also use a clear vanilla extract, which won’t add any color to the frosting.

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🛠 Tools Needed:

Click the links below for my favorite tool recommendations.

• Baking Scale
  • Sourdough starter can weigh differently from person to person, so weighing your ingredients is the best option if you can!
• Whisk
  • For whisking the milk, sugar, and sourdough discard roux together as it cooks.
• Spatula
  • For scraping the sides of the bowl.
• Stand mixer (recommended)
  • A stand mixer with the whisk attachment works best for this sourdough frosting.
  • Alternatively, you can use an electric hand mixer to cream the butter and mix the frosting.

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🛒 Ingredients Needed:

Click on the links below for my ingredient recommendations.

• Whole milk
  • I use whole milk for a balanced and rich flavor, but you could use 2% milk, or a plant-based alternative.
  • For a richer flavor, add 50% half-and-half or heavy cream.
• Granulated sugar
  • The granulated sugar is cooked with the milk and sourdough, so it will not be grainy when you actually mix the frosting.
  • Sourdough frosting isn’t as sweet as traditional buttercreams, so if you want a sweeter frosting, you can add powdered sugar to taste during mixing.
• Kosher salt
  • I use Diamond Crystal Kosher Salt. The salt is essential to balance out some of the sweetness and bring out any other flavorings (such as vanilla). Although, if you need to skip it for a low-sodium diet, you can.
• Sourdough Discard (or active starter)
  • You can use either active starter or sourdough discard in this recipe. Don’t use very old sourdough discard or the frosting can have an unpleasant sour taste.
  • If you don’t have an active sourdough starter, learn how to make one in a week following my how-to guide. See my top sourdough starter tips here.
• Unsalted butter, softened
  • For best results, set out the butter for at least an hour to come to room temperature before making the frosting. It should be softened, but not greasy or melted (here’s not the time to use the microwave to heat your butter!).
  • If the butter is too cold, your frosting will curdle. The ideal temperature for your butter in sourdough frosting is around 65-75ºF.
• Vanilla extract
  • Vanilla flavors the frosting and vanilla frosting is the most classic and versatile to use! Other flavor variations are below.
  • For extra vanilla flavor and specks of vanilla, use vanilla bean paste or a whole vanilla bean.

Sourdough Frosting Variations

• Chocolate sourdough frosting: add ⅓ cup of cocoa powder (natural or Dutch-process will work) when you cream the butter and sugar.
• Coffee or mocha sourdough frosting: add a teaspoon of strong coffee or espresso at the end and the same amount of cocoa powder above.
• Floral sourdough frosting: add ½ tsp of rose water, orange blossom water, lavender, or other essense at the end of mixing.
• Peppermint: add ½ teaspoon of peppermint extract at the end of mixing. You can use this instead of my peppermint buttercream for Sourdough Chocolate Peppermint Whoopie Pies.
• Colorful sourdough frosting: add a few drops of food coloring if desired after mixing.
• Lemon or citrus sourdough frosting: whisk in a couple tablespoons of fresh lemon juice (or other citrus) and a tablespoon of lemon, orange, lime, or other citrus zest at the end of mixing. Adjust to taste. Thin it out for a frosting for my Sourdough Lemon Poppy Seed Bundt Cake.
• Cream cheese sourdough frosting: substitute one stick of butter with 8oz of softened cream cheese. This would be great as the filling for my Sourdough Pumpkin Whoopie Pies or to top my Sourdough Cinnamon Rolls.

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👨‍🍳 How to Make Sourdough Frosting

Follow this visual and detailed recipe guide as you make this sourdough frosting.

1. Make the Sourdough Roux

If you haven’t done so, set aside 226 grams (two sticks, one cup) of unsalted butter to soften to room temperature.

In a small saucepan over medium-low heat, whisk together:

• 200 grams (1 cup) of granulated sugar
• ¼ teaspoon of salt
• 200 grams (¾ cup) of whole milk
• 80 grams (⅓ cup) of sourdough discard (or active starter).

Bring the the mixture to a simmer, whisking constantly, until it thickens into a roux and leaves trails of your whisk in the saucepan, only a few minutes.

Remove from the heat, scrape the roux into a small mixing bowl to cool to room temperature (this can take anywhere from 30 minutes to an hour).

Cover the bowl with plastic wrap to prevent a film from occurring. You can also refrigerate the roux to make a few days ahead of time. Bring to room temperature before using.

2. Whip the Butter

Add 226 grams (1 cup, or two sticks) of softened unsalted butter to the bowl of a stand mixer fitted with the whisk attachment.

Whip the butter for a few minutes, until it’s light and fluffy. Scrape the sides of the bowl with a spatula as needeed.

Alternatively, you can use an electric hand mixer to whip the butter.

3. Mix the Frosting

While mixing on medium speed, spoon in the room temperature sourdough roux to the whipped butter, one spoonful at a time.

Adding the mixture slowly is key to make sure the mixture stays smooth, light, and fluffy (like making brioche).

Continue adding until the sourdough frosting is very smooth and airy. This can take several minutes but will be worth every second! Scrape down the sides of the bowl with a spatula while mixing.

Add in a teaspoon of vanilla extract at the end of mixing.

Before using, taste the frosting (a treat!). This is now the time to adjust any flavorings, sweetness levels, or texture. Add more vanilla if needed, a tablespoon of powdered sugar at a time for more sweetness, or a small amount of whole milk if the texture is too thick.

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🧁 How to Serve

You can use this sourdough frosting to frost and decorate cakes, cupcakes, or sandwich in between whoopie pies.

The flavor is similar to a lighter cream cheese frosting, so it goes particularly well with red velvet cakes, carrot cake, spice cakes, or pumpkin desserts.

Despite how light weight the frosting is, it’s very stable! So you can use it for summer birthdays in the heat without it completely melting like American buttercream or in between cake layers.

The frosting pipes well for intricate patterns, but you do need to watch the temperature of the frosting or it can be difficult to smooth out if it gets too cold and curdles.

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🎂 How to Store

Sourdough frosting stores extremely well, up to a week in the refrigerator.

Store it in an airtight container so it doesn’t pick up any refrigerator odors.

Before using, set it out to bring to room temperature for at least an hour and then rewhip it if needed to make it lighter and fluffy again.

I generally don’t recommend freezing frosting, but you can also freeze it for a few months. Then, thaw in the refrigerator and re-whip.

After frosting on a baked good, it will last 2-3 days at room temperature. After this period, you should refrigerate.

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❓ FAQs:

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Other Sourdough Dessert Recipes You May Enjoy:

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