In short: Hydration is the proportion of water to flour weight. In laminated yeasted dough it decides whether the dough handles well under the rolling pin and whether you get an open honeycomb crumb. The video takes three samples of differing hydration from mixing through to the bake.
The question
How does changing hydration affect the quality of croissants? The aim was to run an experiment with three dough samples at different moisture contents, to show clearly how it affects the dough during handling and the finished product. The full process and results are in the video.
What hydration means
Hydration is calculated against flour weight: 500 g of flour and 250 g of liquid is 50 %. In laminated yeasted dough all the recipe liquid counts, including milk and eggs; the butter used for lamination does not.
The working range for croissant dough is narrow. A few percentage points that would pass unnoticed in bread change how the dough behaves at every stage — which is what makes an experiment like this worth running at all.
What water controls
Rolling. Dry dough resists and tears the butter layers; overly wet dough sticks to the pin and stretches unevenly. The plasticity of the dough has to match that of the butter.
Proving. More water means more mobile gluten and a faster prove — but also a greater risk that the piece slumps and the butter runs out.
Crumb. Water turns to steam and pushes the layers apart. Too little gives a dense crumb; too much gives large voids and fused walls instead of an even honeycomb.
Crust. Wetter dough holds steam longer, and the crust comes out thinner.
Running the test yourself
Change one variable only. Flour, butter, yeast, number of folds, proving temperature and oven programme must be identical across the samples, or there is nothing to attribute the difference to.
Mix the samples at the same time and in the same way, weigh everything to the gram and record the dough temperature after mixing. Assess on four points: how the dough behaves under the pin, how much the piece grew during proving, the height of the baked croissant and what the section shows.
The results of the three samples and my conclusions are in the video above.
Frequently asked questions
What counts as hydration in laminated dough
All the recipe liquid relative to flour weight: water, milk and eggs. Lamination butter does not count.
Why does butter leak from my croissants
The dough and butter were at different plasticity, or the prove was too warm. Hydration affects this indirectly: wetter dough is softer and reacts more to heat.
Can I just add water if the dough feels stiff
Not to dough already mixed — the water will not distribute evenly. Hydration is set at the recipe stage; stiff dough is usually fixed by a rest.