What Is Sourdough Hydration? A Detailed Explanation

Short answer: hydration is the weight of water divided by the weight of flour, expressed as a percentage. 75% hydration means 75g water per 100g flour. Higher hydration = more open crumb but harder to handle.

The basic math

Hydration % = (water weight / flour weight) × 100

For 500g flour and 350g water:

• Hydration = 350 / 500 × 100 = 70%

For 500g flour and 400g water:

• Hydration = 400 / 500 × 100 = 80%

Hydration ranges by bread type

These are guidelines. Within each range, your flour determines what works.

Why hydration matters

Higher hydration:

• More open crumb (bigger holes)
• Tender bread
• Better keeping
• Stickier dough (harder to handle)

Lower hydration:

• Tighter crumb
• Sturdier bread
• Easier to shape
• Sandwich-friendly

Different breads want different hydration.

What flour can handle

Push past your flour's limit and you get a slack, spreading dough.

How to know your flour's protein

Check the bag:

• Protein per 100g flour
• 12g protein = 12% protein

If you can't find it:

• King Arthur bread flour: 12.7%
• Bob's Red Mill bread flour: 12.5%
• Generic AP flour: 10–11%
• Generic bread flour: 12%

Including starter in hydration

A 100% hydration starter (50/50 flour and water) contributes to total hydration:

• 100g starter = 50g flour + 50g water
• For total dough hydration, add starter flour and water to recipe totals

For most home bakers, this can be ignored without dramatic effect.

A scaling example

Recipe: 500g flour, 350g water (70%).

Want to test 75%?

• Same 500g flour
• Increase water to 375g (500 × 0.75)
• Same other ingredients

The dough will be wetter and harder to handle but should produce a more open crumb.

Why "high hydration is better"

The myth: higher hydration = better bread.

The reality:

• High hydration produces open crumb
• High hydration is harder to handle
• High hydration requires good technique
• Many great breads are 65–70%

Don't chase hydration for its own sake. Chase the bread you want.

When low hydration is right

Sandwich bread should be 65%:

• Tight, even crumb
• Holds together
• Good for slicing

A 75% hydration sandwich loaf is too open and tears in slicing.

When high hydration is right

Tartine-style boules want 78–82%:

• Open crumb (the iconic look)
• Chewy texture
• Bakery-quality result

A 70% hydration "tartine" doesn't have the right character.

How hydration affects fermentation

Higher hydration:

• Faster fermentation (more water = more enzyme activity)
• Easier gas expansion (water lubricates)
• More obvious visual signs

Lower hydration:

• Slower fermentation
• Tighter dough resists rise
• Visual signs are subtler

Adjust bulk timing based on hydration.

A practice progression

To learn hydration:

• Bake 5 loaves at 70%
• Bake 5 at 75%
• Bake 5 at 80%
• Compare results

You'll quickly see what your flour and technique can handle.

Hydration vs. tackiness

A dough at 80% hydration feels:

• Tacky (sticks to fingers slightly)
• Soft (jiggles)
• Smooth (after development)

A dough at 80% should NOT feel:

• Wet (drippy)
• Like batter
• Unworkable

If yours does, your flour can't handle 80% — drop to 75%.

A final note

Hydration is one of the most important variables in sourdough.

Once you understand how to measure, calculate, and adjust hydration, you can:

• Match any bread style
• Adapt recipes
• Develop your own
• Communicate clearly with other bakers

Start at 70% if you're new. Push to 75% once that feels easy. 80%+ is for experienced hands.

The goal isn't the highest hydration — it's the bread you want.