If you've spent time in sourdough circles online, you’ve probably come across the float test. The idea is simple: drop a spoonful of your sourdough starter into a glass of water. If it floats, it’s supposedly ready to bake with. But is this test really the gold standard for judging starter readiness?
Let’s break down what the float test is, why it’s not always reliable, and better ways to tell if your starter is truly at its peak.
What Is the Float Test?
The float test is a quick check some bakers use to see if their sourdough starter is ready to use. Here’s how it works:
- Fill a glass with room-temperature water
- Take a spoonful of starter
- Gently drop it into the water
If it floats, the theory goes, it’s full of gas bubbles and fermentation activity, meaning it’s strong enough to raise your dough.
At face value, it sounds like a great trick; easy, fast, and visual. But while it can give you a rough idea, the float test isn’t always as reliable as it seems.
Why the Float Test Isn’t Always Reliable
Some active starters don’t float
You might have a perfectly active, well-fed starter that still sinks like a stone. Why? Texture. If your starter is a little runny or has a higher hydration level, it’s more likely to disperse in the water rather than float even if it’s strong and bubbly.
Whole grain flours are denser
Starters made with whole wheat, rye, or other heavier flours often won’t float, even when they’re at peak fermentation. The bran and germ in whole grain flours weigh the starter down. That doesn't mean it's weak, it just means it’s heavier.
A floating starter isn’t always a strong starter
Just because a starter floats doesn’t guarantee it’s ready. If your starter has developed a lot of surface gas but hasn’t fully fermented, it might still pass the float test while lacking the strength to raise a loaf. Think of it like a soda bottle that fizzes. It looks active but might not have the backbone for a long fermentation.
Better Ways to Tell If Your Starter Is Ready
1. It doubles in size within 4 to 6 hours of feeding
This is one of the clearest signs of an active, healthy starter. After a feed, mark the jar with a rubber band or piece of tape. If your starter doubles (or even triples) within a few hours, it’s got plenty of rising power.
Beginner tip: Use a clear glass jar to make it easier to spot growth and bubbles.
2. It’s full of bubbles and has an airy texture
When you open your jar, your starter should look lively, puffy, light, and riddled with bubbles. This shows that carbon dioxide is being produced and trapped within the structure, which is exactly what you want in your dough.
3. It smells pleasantly tangy
A healthy starter has a clean, slightly sour, sometimes fruity smell. If it smells sharp or tangy (a little like yoghurt or apple cider vinegar), fermentation is ticking along nicely. If it smells foul or too acidic, it might need a few feedings to reset.
Should You Still Try the Float Test?
Sure! The float test can still be fun to try, especially when you’re first starting out. It’s a visual cue and gives you a sense of how fermentation changes your starter over time.
But it shouldn’t be the only test you rely on. Starters behave differently depending on flour type, hydration, temperature, and how recently they were fed. You’ll get better results by observing your starter directly; watching its rise, checking its texture, and trusting your nose.
Final Thoughts
The float test might be a helpful trick now and then, but it’s far from foolproof. A better approach is to look at the bigger picture. Ask yourself:
- Has it doubled in size since feeding?
- Is it bubbly and full of life?
- Does it smell pleasantly fermented?
If the answer is yes, your starter is good to go whether it floats or not.
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