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Sourdough Float Test: How To Tell If Your Starter Is Ready

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There’s a lot of debate as to whether or not the sourdough float test is a worthy gauge of starter activity. But as a long-time sourdough baker, I think it’s a topic worth visiting.

Believe it or not, the float test has helped me figure out if my timing is on point, many times.

Sometimes it can seem hard to figure this sourdough thing out. Like, we just want to know whether or not our sourdough starter is ready to bake with. Is that really so much to ask?

Doing a quick and easy sourdough float test may help with that.

active sourdough starter floating on top of a mason jar

what is the sourdough float test?

The float test involves taking a small amount of starter and dropping it into a cup of water to see if it floats. If the starter floats, it means that there is enough gas produced by the yeast and bacteria in the starter. Enough meaning, enough to make the bread rise. In other words, the starter is ready to be used for baking sourdough bread.

As a regular baker of sourdough, I rely on the float test to determine whether my starter is fully ready for baking. Now, some might disagree that the float test is an accurate indicator of a healthy sourdough starter. And it’s true, there’s more to making a starter work than it simply passing the float test. But let’s talk about some of the science behind it.

When you feed your sourdough starter, the yeast and bacteria in the starter consume the flour and water, producing carbon dioxide gas as a byproduct. The gas gets trapped in the gluten network of the dough, which causes it to rise. If there is not enough gas produced by the yeast and bacteria, the dough will obviously not rise properly, resulting in a dense and heavy sourdough bread.

So, if you’re struggling with dense, heavy or gummy loaves, and want to ensure your starter is at peak activity, it just might be a good idea to try the float test.

The sourdough float test is a simple and effective way to determine whether your starter has enough gas to make bread rise. By understanding the science behind the float test, you can help your sourdough bread turn out light, fluffy, and delicious every time.

how to prepare your starter for the float test

Before performing the float test, you need to make sure your sourdough starter is active and healthy. To do this, there are a couple of steps to follow.

First, feed your starter. I always feed my sourdough starter at least 6-12 hours before performing the float test. This ensures that the starter is active and has enough wild yeast to produce the desired result. The length of time will vary based on how much you feed and the temperature of your home.

When feeding your starter, make sure to use equal parts of flour and water. Take into account how much starter you already have, and feed it at least the same amount by weight.

Honestly, I never measure or weigh my starter when I feed. I’ve learned how to eyeball about how much starter I have, and then I feed it at least that same amount. But you certainly can measure it, if you want to be sure.

Second, know how to recognize an active starter. An active sourdough starter should have a bubbly and frothy texture. You should be able to see a noticeable increase in volume after feeding it. If your starter isn’t showing any of these signs of activity, it probably won’t pass the float test anyway.

Lastly, it’s important to make sure your starter is at room temperature before you do the float test. If it’s too cold or too warm, you may not get accurate results.

active and bubbly sourdough starter from an aerial view

how to perform the sourdough float test

a step-by-step guide to the sourdough float test

If you’re new to sourdough baking, the float test is a quick and easy way to check if your sourdough starter is ready to use. All you have to do is drop a small amount of active, unstirred sourdough starter into a glass of water and observe whether the starter rises to the top or sinks to the bottom. The only items you need to perform the float test are a small amount of sourdough starter and a glass of water.

It really is simple. But let me give you a little more confidence by breaking this down into three easy steps:

  1. Understand the factors that affect the float test (I’ll cover these more in a minute). If you know that you used a less glutenous flour or your starter is young, take that into consideration before trying the test.
  2. Take a small amount of your sourdough starter and drop it into a glass of water. Remember not to stir it first.
  3. Now observe whether the starter floats or sinks. If it floats, it’s ready to use. If it sinks, it needs more time to ferment.

consider the timing

Keep in mind that timing is an important factor when performing the float test. Observe your starter, and time the test based on your starter’s signs of activity. A good way to know your starter is ready for the float test is when it has doubled in size and has lots of beautiful bubbles on the surface. This usually takes 6 to 12 hours after feeding.

It’s also important to note, the float test is not always accurate and can sometimes give a false positive or false negative. So it really is best to use the float test in combination with other methods to determine if your starter is ready for baking.

Let’s dive deeper into how to interpret the results of the float test, along with some of the factors that affect its accuracy.

interpreting the results of the float test

There are basically two possible outcomes when performing the sourdough float test. Either your starter floats on top of the water, or it sinks down into the glass.

A positive result is when your sourdough starter floats in the glass of water. A bubbly starter floating to the top of the water is a good indicator that the yeast is active, and that there are enough gas bubbles to create a light and airy bread. Congratulations, your starter is ready to be used in bread-making! (As long as you know it’s fully mature, at least around 4-6 weeks old)

As we talked about before, the sourdough float test is not always accurate. A false positive can happen when there are lots of bubbles in the starter, but the starter isn’t actually mature enough to bake great bread. A starter that is less than 4 weeks old may pass the float test, despite the fact that the bacteria and yeasts needed to make great bread aren’t fully activated.

In other words, I would not expect a starter that is less than 4 weeks old to make airy bread, even if it passes the float test.

Now, a false negative can happen if the starter is too dense or has too much flour in it. A starter fed with rye flour or whole wheat flour is more likely to produce a false negative. The starter may be ready to use, even though it did not pass the float test.

Other reasons you may get a false negative result:

  • Stirring the starter before performing the test
  • Testing after the starter has passed its peak, but is still viable for baking bread
sourdough starter being poured onto flour to make dough

factors affecting the float test

As a sourdough baker, I use the float test is an essential tool for determining whether my starter is ready to use. However, just as important as knowing how to perform the float test, is understanding the several factors that can affect the accuracy of it.

factor #1: type of flour being used

The type of flour that you use to feed your starter can affect the results of the float test. Whole wheat flour, rye flour, and all-purpose flour can all produce different results. Specifically, whole grain flours can make your starter more dense, causing it to sink in water even in an active state. On the other hand, all-purpose flour makes for a more light and airy starter, which has the potential to float even when it is not completely ready.

factor #2: hydration status

Hydration can also affect whether or not your starter passes the float test. If you keep your starter at a high hydration (a more runny or watery consistency), it is likely to sink when put in water. Although starter of a thinner consistency can still work for baking bread, it tends to lend itself best to recipes when it’s kept at the hydration level of a thick pancake batter. (It also makes it easier to make really quick but delicious sourdough pancakes.)

factor #3: temperature and environment

Temperature and environment can potentially affect the float test, as well. Warm spots in your kitchen can cause your starter to rise faster, making it appear ready when it is not. Similarly, a cold environment can slow down the fermentation process, making it take longer for your starter to be ready. It’s very helpful to keep your starter in a consistent environment to keep it healthy, and to get accurate results with the float test.

factor #4: age of starter

Finally, the age of a sourdough starter can play a factor in the results of the float test. If a starter is too young (younger than 4 to 6 weeks), there is a higher possibility of getting a false positive.

doing the sourdough float test in a glass of water

troubleshooting common issues

how to solve float test failures

So, let’s say your starter does not pass the float test. Sometimes, even after hours of feeding and waiting, this can happen. Yes, it is frustrating, but there are a few things you can try in order to troubleshoot.

First, if your starter has been left for a long time without feeding, it may have lost its strength and become too weak to pass the float test. This is a common issue if you bake less often, storing your starter in the fridge for a week or more at a time. Try refreshing your starter by discarding most of it, and doing a few more feedings with fresh flour and water. Leave it on the counter and feed it every 24 hours for a few days. This is the best way to give it a boost, and then hopefully pass the float test.

The second reason your starter may not be passing the float test is that it is too young. If your starter is brand new (less than a week old), there is a very good chance that it hasn’t yet developed enough yeast and bacteria to pass the float test. Be patient and keep feeding your starter regularly until it becomes more mature.

Lastly, if your starter is made with a low-gluten flour, like rye flour, it may have a lower rise and not pass the float test. If this is the case, and your starter is showing all the other signs of activity (bubbles on top, doubling in size, having a spongelike look when you peer through the jar), then go ahead and bake with it. Or you could try feeding your starter with some higher protein flour, such as bread flour or whole wheat flour, to give it a better chance of passing the test.

bubbly sourdough starter in glass jar

how to revive a young or weak starter

If your starter isn’t passing the float test because it is young or weak, there are a few things you can do to revive it.

Make sure you are feeding your starter regularly, at least once a day. Leave it on the counter so the wild yeasts have plenty of opportunity to grow. If you are discarding a lot of your starter each time you feed it, reduce the amount you discard, and increase the amount you feed. This will help your starter grow stronger and become more active.

I never actually throw starter away. I always use my discard, which is just inactive starter. If you’re concerned about ending up with too much sourdough starter, download my Sourdough Discard Favorites ebook by entering your email below. You’ll have plenty of easy ways to use up your starter!

If your starter is still struggling, try changing the environment it is in. Make sure it’s kept at a warm temperature, between 70-80°F, and away from any drafts or direct sunlight. This creates a more favorable environment for the yeast and bacteria to grow and thrive.

using sourdough starter after the float test

So you’ve done the float test, and have determined that it’s ready to bake with! Time to move on and use it in your bread recipe of choice. My favorites are my classic rustic sourdough bread, chocolate chip sourdough bread, or cinnamon swirl sourdough sandwich bread

One thing to keep in mind is that your mature starter will not stay at its peak for very long. If your starter is active and ready to bake with, but you can’t use it right away, you can store it in the refrigerator to slow down the fermentation process a little. However, I wouldn’t wait more than 6 hours or so, even after putting it in the fridge. Once you are ready to bake, take it out of the fridge and let it come to room temperature before using it.

How often should I do the float test?

Now that you’ve practiced the float test, don’t feel like you have to do it every time you use your starter. If it makes the most sense for your specific situation, do it. If it doesn’t, don’t.

In my situation, I do it almost every time I start a batch of dough. Because I use exclusively all-purpose flour for feeding my starter, and typically always do a 1:1 feeding ratio, I find the float test to be very reliable. It also gives me peace of mind that I’m catching my starter at or near peak activity.

If you start noticing that your bread isn’t rising like it should, you can always try the float test next time you bake. It’s a great way to check and make sure you’re catching your starter at its peak.

Basically, the float test is a great way to determine if your sourdough starter is mature and ready to bake with. But, it isn’t the only way to assess starter readiness. It’s just meant to be another tool in your belt!

sourdough starter being poured over flour in bowl to make dough

alternative methods to assess starter readiness

When it comes to determining whether a sourdough starter is ready for baking, the float test is a popular method. However, it’s not the only way to assess the readiness of your starter. There are a few other ways that can help you determine whether your starter is ready to use. I recommend using them in conjunction with the float test.

Here are the other things you should be looking for in a mature starter, besides passing the float test:

  • A pleasant, tangy aroma
  • Lots of bubbles
  • A noticeable increase in volume after feeding

If you struggle with being able to tell if your starter has expanded in volume, mark the level of the starter in the container with a rubber band or tape immediately after feeding. This way, you can see the change as it expands.

​sourdough float test conclusions

To conclude, the float test is usually a reliable method for assessing the readiness of your sourdough starter. However, it isn’t always necessary. You can still achieve the best results for your sourdough bread by using alternative methods, and not solely relying on the float test. I’ve just found the float test to be a helpful tool in catching my starter at peak activity. That gives me the confidence in being set up for the best rise possible.

Performing the float test is a great thing to do alongside practicing your sourdough baking. Before you know it, it will be like second nature to tell whether or not your starter is ready to bake with. Don’t be discouraged as you continue to learn how to use your sourdough starter. Keep baking and you will see success!

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