Deep Dive
Beyond the Bottle: Decoding Free vs. Bound Water in Bread Hydration
In the world of artisan baking, hydration is often simplified to a single number: the ratio of water to flour. However, as you move into advanced techniques involving seeds, grains, porridges or starters, the maths becomes more nuanced. To truly master your dough, you must distinguish between free water and bound water.
Two doughs at "78% hydration" can feel completely different in your hands. One is a slack, glossy, almost soupy mess. The other is firm and pliable, almost stiff. The recipe card lies. Or rather, it tells only half of the story. The other half is which water is doing what.
The Basic Formula: What Counts Initially?
At its most fundamental level, hydration refers to the total quantity of moisture in a dough relative to the total weight of the flour. The calculation divides the weight of all water-containing liquids (including milk, tea or juice) by the total flour weight.
The textbook formula
Hydration % = (Total water weight ÷ Total flour weight) × 100
For sourdough bakers, this includes the water and flour tucked inside the starter. If you use 100 g of a 100% hydration starter, you are adding 50 g of flour and 50 g of water to your total formula. This nuance is covered in detail in The Master's Ratio.
Free Water: The Architect of Gluten
Free water is the liquid available to interact directly with the flour's proteins (gliadin and glutenin) to develop the gluten network. It is the water you pour straight into the mixing bowl. It dictates the immediate "feel" of the dough, whether it is stiff, manageable, or a slack high-hydration puddle.
High levels of free water promote better extensibility and faster fermentation, but they also make the dough stickier and harder to shape. When experienced bakers say a dough "feels" 75% versus 85%, they are intuitively reading the free-water content. The recipe card may show one number, but their hands feel another.
Bound Water: The Moisture Reserve
Bound water is moisture that is physically or chemically locked away within other ingredients. Because it is not free to interact with the flour proteins, it does not contribute to initial gluten development or to the dough's handling properties. It is, however, far from useless: it is the secret to long shelf life and a tender crumb.
The role of soakers
Soakers are inclusions like seeds, nuts or whole grains that are submerged in liquid before being added to the dough.
- Why we use them: dry seeds are thirsty. Added raw, they will draw moisture away from the dough during proofing, leading to an under-hydrated, crumbly loaf.
- The hydration nuance: water locked inside a soaked grain does not hydrate the dough texture. It acts as a moisture reserve, slowly releasing water over time to keep the finished crumb moist for longer.
Porridges, scalds, tangzhong and yudane
Cooked-starch inclusions take bound water a step further through gelatinisation. When starch is heated with water above roughly 65°C (150°F), the granules swell and burst, forming a gel that physically traps moisture in its matrix. The resulting dough holds far more water than raw flour ever could, and the bread stays fresh for days because the trapped water cannot easily evaporate.
Two specific techniques get conflated in English-language recipe writing: tangzhong (Chinese) and yudane (Japanese). Both names translate roughly to "boiled dough", and you will also see them under English labels: water roux for tangzhong, yukone for yudane, and the broader flour scald in European traditions (often applied to rye or whole grain). They share a goal but produce different doughs.
| Tangzhong | Yudane | |
|---|---|---|
| Flour : water | 1:5 (occasionally 1:4) | 1:1 (up to 1:1.5) |
| Method | Cooked on the stove until thick | Boiling water poured onto flour, no stovetop |
| Consistency | Smooth, pourable paste | Stiff, clumpy, dough-like |
| % of total flour | 4–10% | 10–25% |
| Resting | Cool to room temp, ready to use | Best after 4–24 h in the fridge |
| Crumb | Light, feathery (shokupan, milk bread) | Mochi-like chew (cinnamon rolls, enriched buns) |
One practical gotcha for tangzhong: because it is actively cooked, water evaporates during preparation. Weigh the cooled roux and top it back up to the original combined weight, otherwise your loaf will be drier than the formula promises. Yudane has no such problem because the boiling water goes straight into the bowl and is covered immediately.
Both behave as sub-recipes of the main dough, and they scale exactly the same way as a levain or a soaker. See the sub-recipe scaling rule in The Master's Ratio: doubling the loaf doubles the tangzhong, and the internal 1:5 ratio stays put.
The takeaway either way: a "high hydration" loaf with a tangzhong is structurally a different beast from a "high hydration" loaf where every gram of water is poured straight into the autolyse. The total weight is the same. The behaviour is not.
What hydration does your gluten actually feel?
A soaker locks water inside the inclusion. The slider controls how much of the soaker's water stays bound (locked in the seeds) versus leaks back as free water available to the gluten.
Gap: 11.7%. That's how much "wetness" is hiding inside the soaker instead of building gluten.
What Should You Ignore in Your Maths?
Almost everything in your kitchen contains some water, but professional baker's maths generally excludes the following from the hydration percentage:
| Ingredient | Counted as water? | Why |
|---|---|---|
| Water, milk, juice, tea | Yes, fully | Free water available to the gluten |
| Eggs | Usually no | Proteins and fats dominate the functional impact |
| Butter, oil | No | Fats coat gluten rather than hydrate it |
| Fresh fruit (blueberries, apple) | No | Water is trapped in cellular structure |
| Soaker / porridge water | It depends | Partially bound. The slider above is the honest answer |
Fats and proteins like butter, oils and eggs are not typically counted as part of the hydration even though they have significant functional impacts on dough softness and richness. Fresh fruits like blueberries or apples contain water, but because that moisture is trapped within the cellular structure of the fruit, it is not considered free water for the formula.
Practical Strategy: The Bassinage Method
When experimenting with soakers or porridges, the "true" hydration can be difficult to predict because some water may leak from the inclusion into the dough as fermentation progresses. The professional response to this uncertainty is bassinage, also known as double hydration.
The technique is simple: hold back 5–10% of the recipe's water during the initial mix. Once your inclusions are fully incorporated and you can read the dough's strength, slowly add the remaining water until the texture feels just right: glossy and extensible, without becoming a soupy mess. Bassinage trades a single decision at the bowl for a series of small, reversible ones during the mix.
The bassinage formula
Total water = Flour × Target hydration ÷ 100Reserve = Total water × Hold-back %Initial water = Total water − Reserve
Bassinage planner
Plan how much water to mix in first, and how much to hold back for the second addition.
The Two-Number Mental Model
The next time you read a recipe, train yourself to ask two questions instead of one:
- What is the on-paper hydration? The classic ratio. This sets your expectation for shelf life, crumb openness and oven spring.
- What free-water hydration will my hands feel? Subtract the water hidden in soakers, scalds and porridges. This sets your expectation for stickiness, shaping difficulty and the speed of gluten development.
Once you separate these two numbers in your head, mysterious doughs stop being mysterious. A 90% hydration loaf with a heavy oat porridge is not a "wet dough". It is a moderately hydrated dough with a moisture reserve baked in. A 75% hydration loaf with a mountain of dry seeds folded in at the end is not a "moderate dough". It is a wet dough that is about to dry out as the seeds drink.
The recipe is not lying. It is just only telling you half of the story. Now you can read the other half.