Lemon Rhubarb Sourdough Discard Cake

By Amanda Paa – Updated June 17, 2022
5 from 13 votes
This lemony rhubarb cake is incredibly moist with a light and airy crumb thanks to sourdough discard! The soft texture has rhubarb in each bite, complemented by honey and lemon zest to bring out its flavor. You won't taste any sourness in this cake, and it's a great way to use up sourdough discard that you have in the refrigerator.
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rhubarb cake slices stacked on one another

You’re probably noticing a theme here: rhubarb recipes galore. I love the long stalks of pinkish-red beauty for making everything from gluten-free rhubarb crisp to muffins, and margaritas. And now cake! Paired with another favorite ingredient: sourdough discard.

This incredibly tender, melt-in-your mouth rhubarb cake has notes of lemon and honey, along with the sweet-tart nubs of rhubarb folded in. I can’t even describe how delicious the delicate crumb is, and the airiness of each bite!

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It’s the kind of cake you can have for dessert with a dollop of whipped cream, snack on straight from the fridge, or eat for breakfast.

You’ll be amazed at how flavorful it is, but probably even more amazed at the ideal texture it has. Light and fluffy, but still firm enough so you can pick up a piece and eat it from your hand, no fork needed.

sourdough discard rhubarb cake up close photo

What does sourdough discard do for cakes?

Sourdough discard doesn’t make cakes taste sour. Instead, it makes them fluffy and soft because it increases the acidity of the cake batter, which weakens the gluten in flour. And because it has already been fermented, the gluten in the sourdough discard itself has also been weakened. It has the same effect in this fabulous Sourdough Discard Pumpkin Bread.

The other thing discard does in baking is bring out the flavors of other ingredients in the recipe. This is due to the naturally occurring alcohols that develop in sourdough starter, and alcohol is a flavor enhancer. That means the main components of this cake; rhubarb, lemon, and honey – really shine.

ingredients for sourdough rhubarb cake
rhubarb cake batter
sourdough discard rhubarb

How to make this sourdough discard cake:

  1. Chop and slice your rhubarb.
  2. Whisk dry ingredients together and set aside.
  3. With a stand mixer or hand mixer, you’ll beat the oil with sugar and lemon zest. This helps the sugar dissolve, and releases the oils of the lemon zest.
  4. Add eggs and mix until frothy. Then add remaining liquid ingredients. Mix on medium low until combined.
  5. Add dry mixture and mix just until dry flour bits disappear.
  6. Gently fold in rhubarb. Spread batter in pan.
  7. Decorate top of cake with longer rhubarb spears, in whatever pattern you’d like.
  8. Bake at 350 degrees F for 30 minutes, then 330 degrees F for 12-15 minutes more.
sourdough rhubarb cake in a silver pan
sourdough rhubarb cake cut into pieces in a baking pan

How long is sourdough discard good for?

You can keep sourdough discard in your refrigerator for up to 10 days. The discard will be more sour the longer it stays in the fridge. So for something like this cake or these zucchini muffins, where I don’t want the sourness to come through, I use discard that is less than 5 days old.

Your discard might accumulate a little liquid on the top while it’s in the fridge, which is called hooch, simply meaning alcohol that is the byproduct of fermentation. You can simple pour the liquid off into garbage, and scrape the very top off, and use the rest as discard.

What to look for when buying or picking rhubarb:

Rhubarb differs slightly in color depending on the variety, the stalks ranging from green, pink, and red. Red stemmed types are not necessarily sweeter, because color and sweetness are not always related. But they do make for prettier desserts, so if you’re going for looks, try to find a red or pink variety.

Rhubarb is most tender and flavorful in spring and early summer but can be used throughout the season. Select firm, crisp stalks when they are 8 to 15 inches long. To harvest, twist off the leaf stalk at the soil line rather than taking a knife and cutting near the roots. Finally, cut off the leaf.

sourdough discard cake with whipped cream on a pink plate

More Sourdough Discard Recipes:

sourdough discard rhubarb cake in a square pan with bowl of whipped cream to the left.

Moist Rhubarb Sourdough Discard Cake

This delicious rhubarb cake is incredibly moist with a light and airy crumb thanks to sourdough discard! The soft texture has rhubarb in each bite, complemented by lemon zest to bring out its flavor.
5 from 13 votes
Prep Time :15 minutes
Cook Time :45 minutes
Yield: 1 (8-inch) cake
Author: Amanda Paa

SCALE:

Ingredients

  • 8 ounces fresh rhubarb, 3/4 of the rhubarb cut into 1/2 inch chunks, and remaining cut into pieces that fit inside the pan diagonally to create a pattern
  • 170 grams all purpose flour
  • 1 1/2 teaspoons baking powder
  • 1/2 teaspoon fine salt
  • 155 grams cane sugar
  • 1/2 cup sunflower or grapeseed oil
  • 1 tablespoon lemon zest
  • 2 eggs, room temperature
  • 3 tablespoons runny honey
  • 65 grams sourdough discard, preferably room temperature
  • 1 1/2 teaspoons vanilla extract
  • 1 teaspoon fresh lemon juice
  • 3 tablespoons whole milk

Equipment

  • 1 8-inch square cake pan

Instructions 

  • Preheat oven to 350 degrees F. Grease and line a square 8-inch cake pan.
  • Add chopped rhubarb to a medium bowl.
  • In another medium bowl, whisk together flour, baking powder, and salt. Scoop 2 heaping teaspoons from this mixture and add it to bowl with chopped rhubarb. Toss to combine (this lightly coats the rhubarb so it doesn’t sink in the cake). Set aside.
  • In a stand mixer or with a hand mixer, on medium speed beat 145 grams sugar with the oil and lemon zest for 1 1/2 minutes (this helps to dissolve the sugar). Then add eggs, and beat for 1 minute on medium speed, so that the mixture is frothy.
  • Add honey, sourdough discard, vanilla extract, lemon juice, and milk, and mix on medium speed until just combined. Then add in dry mixture on low speed, just until no bits of flour remain.
  • Gently fold in rhubarb (it's okay if you can see a little flour on the rhubarb when its in the batter.) Place batter into greased and line 8-inch cake pan, and smooth top. Add the longer pieces of rhubarb to the top, in any pattern you'd like. Sprinkle top of cake with 2 heaping teaspoons sugar. Bake for 30 minutes at 350 degrees F, then turn oven down to 330 degrees F and bake for 12-15 minutes more, until toothpick comes out with a few moist (but not wet) crumbs. Remove from oven and let cool on cooling rack.
  • In a sealed container, this cake stores very well in the refrigerator for up to 4 days.

Did you make this?

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June 17, 2022

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24 comments

  1. Lisa

    5 stars
    Turned out brilliant! I didn’t have a lemon so substituted Lime and it was delicious. I also skipped the Rhubarb diagonal topping as my Rhubarb was already chopped and I just added a bit more chopped to the mix. I used a 9″ round pan because I couldn’t find the square one haha. I wish there was an option to post a photo. It was so fluffy and just the right amount of tart and sweetness!

    • Amanda Paa

      Yay, so glad you liked the cake! And yeah, chopped rhubarb on top totally works if you want to skip the diagonals!

  2. Linda

    What is the sour dough discard recioe please and thank you.

  3. Connie

    5 stars
    Great recipe. I increased the rhubarb from 8oz to 27oz because rhubarb is more important than cake. Love how it turned out!

    • Joy

      Amazing

  4. Heidi DePaula

    5 stars
    This was my first time making anything with Rhubarb. Next year I’ll be asking my friends for some rather than waiting for them to offload it on me. This cake was delicious! I doubled the recipe and shared it with my in-laws and they really liked it as well as my husband and 4 kids! Will be making it again.

    • Amanda Paa

      i’m so glad that your family enjoyed it! and what a fun introduction to rhubarb.

  5. Colleen

    5 stars
    This cake is some light and fluffy! I’m thinking about experimenting with different fruits when rhubarb season is over!

    • Amanda Paa

      I’m so glad you liked it! And yes, I think it would great with other fruits too, like apple!

  6. Anne M

    5 stars
    So incredibly delicious! LOVE this cake. It’s the best.

    • Amanda Paa

      Yay, glad to hear that! Thank you for making the recipe!

  7. Shawn Augustine

    5 stars
    Great recipe! Always looking for creative ways to use Rhubarb and I saw this come across my feed using some Sourdough discard, which I have plenty of (no one told me my starter would grow so big, so fast, lol!) and my Rhubarb was ready for some picking! I made a batch for my neighbor initially, for helping us put our garden in, and then couldn’t stop thinking about how delicious it looked and smelled so I made a batch for my family! I did add a little almond extract in place of the vanilla and that gave it a nice hint of almond. Will definitely be making this again! Thank you Amanda for always sharing such great recipes! ❤️

    • Amanda Paa

      Love that you made it twice already! And I love the idea of the almond extract, I’m going to try that as well.

  8. Marty K

    5 stars
    Excellent cake. Amazing moisture, texture and flavour.

    • Amanda Paa

      Glad you enjoyed the cake, thanks for making it!

  9. Karen

    Just wondering why you use two different types of measurements. I have completely changed to grams. I feel it is odd to mix the two. That being said I am going to try this recipe since I love rhubarb.

  10. Robin

    5 stars
    It’s such an easy discard recipe and will be added to my book! The best part is how yummy it is and it’s so pretty.

    • Amanda Paa

      So glad you enjoyed it, Robin! Thanks for making the recipe.

  11. Shannon

    5 stars
    Delicious! I was going to “stage” it for a photo and before I could do that my husband cut a piece and said “This is delicious!”. Easy recipe and great use of rhubarb and discard. Makes a nice little cake for anytime snacking. Made exactly as written.

    • Amanda Paa

      So great to hear, Shannon! And someone cutting into it before you could take a photo, I can related to that! :)

  12. Elizabeth

    5 stars
    I made this yesterday, following the recipe as it was written. It was beautiful and delicious! This will be on rotation for my family!

    • Amanda Paa

      Fabulous, I’m so glad your family enjoyed it Elizabeth!

  13. Susan Cripe

    5 stars
    Moist and delicious! I didn’t have enough lemon zest so I added 1t. lavender buds. It’s a winner!

    • Amanda Paa

      So glad you enjoyed it, and the lavender sounds lovely with rhubarb!