Sourdough Float Test (knowing when starter is ready to use)

The sourdough float test is a great way to know if your sourdough starter is ready to use for baking. It’s not always 100% accurate, but it’s helpful for beginner bakers or when you’re feeling a bit unsure. In this post, I’m sharing what a sourdough float test is, how to do it, and answering all your questions about the process. Let’s dive in! 

starter ready or not words with a glass of water and dough floating in it
Source: Plum Branch Home

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What is the Sourdough Float Test

The sourdough float test is a test where you drop a spoonful of sourdough starter into a glass of water to see if it floats or sinks. If it floats, it’s ready to bake with; if it sinks, it needs to be fed and fermented longer. 

This tests how much trapped carbon dioxide is in the starter from the fermentation process. The trapped carbon dioxide is what causes a rise in bread and baked goods.

Video Tutorial

How to do a Sourdough Float Test

To do the sourdough float test, take a spoonful of starter and gently drop it into a glass of water. If it floats, the starter is ready to use. If it sinks, your starter needs to be fed and set out to ferment on the counter for 4–12 hours. The immediate action of floating or sinking is the best result, not what happens after it’s been sitting for a minute or two in the water.

If you’re baking a recipe that calls for sourdough discard, you can use a starter that fails the float test, aka sinks. It only needs to float when a recipe calls for a fed starter.

ready and not ready starter floating in water glasses
Source: Plum Branch Home

Tips for the Best Results

  • Gently move the spoonful of starter from its jar to the glass of water.
  • Only use room-temperature water or water right out of the faucet set on the middle temperature setting (don’t use too hot or too cold water).
  • Make sure the glass is large enough that the starter doesn’t get stuck on the sides of it.
  • Set the glass on a sturdy, even surface, like the countertop, and don’t move it during the test.
  • Within the first 10–20 seconds of the starter, floating or sinking is the most accurate result, not what happens after 1 to 2 minutes.
starter in a glass of water sunk to the bottom
Source: Plum Branch Home

Sourdough Float Test Fail – What To Do

If your spoonful of starter sinks, everything is okay. You just need to feed your starter and let it sit out at room temperature for 4–12 hours to ferment.

Problems with the Float Test

The sourdough float test is not 100% accurate due to many factors. It’s always best to take into consideration when you last fed the starter, the consistency, and how active it is.

When in doubt, feed the starter, sit it out on the counter, and let it ferment for 4–12 hours before baking with it. It won’t hurt the starter to get another feeding, even if it’s ready.

Starter Hydration Affects Sourdough Float Test

Your starter hydration can affect the float test sometimes. If the starter is runny and not the consistency of a thick pancake batter, it can affect the results.

Flour can Affect the Float Test

Depending on what flour you use, that can affect the results as well. If you use all-purpose flour, you have nothing to worry about. If you use a more dense flour to feed your starter, that’s when it can affect it.

Other Ways to Check Starter Readiness

You don’t have to use the float test every time you bake. Heck, you don’t have to use it at all. I think I’ve only used it two times in the last year. It’s just a helpful tool in case you’re unsure if it’s ready to use. Here are other ways to check if your starter is ready:

  • The consistency is a thick pancake batter.
  • There’s no hooch present (a layer of liquid on top of the starter).
  • It’s been fed within the last 4–12 hours or been in the fridge only 1-2 days after the last feeding. There are visible air bubbles in the starter.
  • The starter has risen in its jar.

Sourdough Float Test FAQ

Is a sourdough float test accurate?

Not always; different things can affect the results, such as starter hydration and thickness. But for the most part, you will get pretty good results. When in doubt, just feed your starter and let it sit for 4–12 hours before using it.

Why should I use the float test if it’s not foolproof?

You don’t have to use it, but it’s a good tool if you’re unsure if your starter is ready for use. Also, it’s a nice way to test the starter before using it in bread recipes to ensure a good rise.

Do I have to do the float test every time I bake with my starter?

No, you don’t have to use the float test at all. It’s up to you if you use it, when you use it, or how often you use it. 

What if the sourdough starter float test sinks?

That’s okay; nothing is wrong with your starter; it just needs to be fed to ferment and create more carbon dioxide. Just give it a good feeding and let it sit on the counter for 4–12 hours. 

What if the sourdough starter float test floats then sinks?

If the starter floats and then sinks immediately, it needs more time to ferment before being used to bake. If the starter floats for a while and then sinks, it’s ready. It’s just been left in the water longer than needed.

The best results are what happens within the first 10-20 seconds, not what happens after sitting in the water for a minute or two. 

Why is my sourdough starter not passing the float test?

It just means your starter needs more time to ferment and create the carbon dioxide gas bubbles that will make it float and rise dough. Make sure when you feed the starter, it’s got the consistency of a thick pancake batter. 

What should I do if my sourdough starter passes the float test?

That means it’s ready to be used in recipes and will rise your bread and baked goods. You don’t need to do anything to it.  

What happens if sourdough starter does not pass the float test?

Nothing bad is going on; just feed it and let it ferment for 4-12 hours before using it. 

So is sourdough starter ready when it floats in water?

Yes, it is. It means the starter cultures are active and ready to be baked with. 

Do I do the float test for just sourdough starter or sourdough bread dough?

You will only do the float test with sourdough starter, not bread dough. 

Why is my sourdough starter bubbling but not rising?

This means your starter is healthy and happy but has too much water (aka hydration). On your next feeding, use less water to get it to a thick pancake batter consistency. 

How long should starter float for the float test?

What happens within the first 10–20 seconds is the most accurate. You don’t need to let it sit any longer than this. 

Do you stir sourdough before the float test?

No, you don’t need to stir the sourdough before the float test. 

Try These Sourdough Recipes with Your Starter

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