Week 10 Bake: Twenty-seven layers of butter

The croissant bake — a détrempe mixed yesterday, an 82% butter block, three letter folds, and a proof that has to stay under the butter

26 April 2027

Last week the butter went into the dough and disappeared into the crumb. This week it stays out of the dough, in one cold slab, and the whole bake is an argument about temperature that you can lose at four separate points.

Before the session#

Mix the détrempe the night before. 500 g bread flour, 200 g water, 100 g milk, 50 g sugar, 10 g salt, 7 g instant yeast and 25 g soft butter — 60% liquid, 10% sugar, 2% salt, 5% butter on flour weight. Mix it to a shaggy, barely developed dough and then stop. You will roll this thing six or seven times tomorrow, and every pass develops gluten; a dough that arrives fully kneaded fights you on the first fold and tears on the third.

Press it into a 20 × 20 cm square about 2 cm thick, wrap it, and refrigerate it overnight. Flat chills evenly. A ball chills from the outside in and hands you a warm middle you cannot see until it smears.

Buy the butter deliberately: unsalted, European-style, 82 to 84% fat, 250 g, which is half your flour weight. Supermarket block butter is 80%, and most of that missing two to four per cent is water dispersed through the fat. More water means a harder, more brittle block at fridge temperature — it snaps when you bend it where the high-fat block yields. You cannot roll a sheet out of something that snaps.

Bring a ruler and a bench scraper. The measurements in this session are not decoration. A butter block 2 cm out of square is a butter block sitting under the edge of the dough, and it comes out the side on the second fold.

In the session#

The room is held at 18 to 19 °C and there is a fridge shelf for every bench. Both of those are equipment.

Two components, then one. The détrempe is the yeasted dough you brought. The beurrage is the butter block: pound the 250 g between two sheets of baking paper into a 16 × 16 cm square roughly 1 cm thick, working it with the pin until it bends without cracking, then chill it back to 16 °C. Roll the détrempe out to 20 × 36 cm, seat the butter square on one half with a 2 cm margin on the three open sides, fold the bare half over it and pinch that margin shut. That is the lock-in. From here the butter is enclosed, and everything you do to the dough you also do to the butter.

The window. Butter is only pliable between about 16 and 20 °C. Below that, too much of the fat is crystalline and the block behaves like a biscuit: it shatters under the pin into shards that puncture the dough, and you see grey flecks breaking the surface. Above it, the crystal network gives up, the butter smears and is absorbed into the flour around it, and your two components become one. Both failures end lamination. Check the block with a probe at every lock-in, and when the dough starts to feel soft under your hands, stop rolling and put it back in the fridge.

The folds. Roll the packet to about 20 × 60 cm and 8 mm thick, working away from you and back along the same axis every time. Rolling sideways stretches some layers and not others, and uneven layers bake into a lopsided crumb. Then a letter fold — thirds, like a business letter — and into the fridge for 30 to 60 minutes. That rest does two jobs at once: the gluten relaxes so the next roll does not fight back, and the butter comes back to the top of its window.

Three letter folds multiply out to 3 × 3 × 3 = 27 layers of butter. A fourth gives 81, and 81 is worse. Sheeted to 3.5 mm, the whole repeat — one butter layer and the dough under it — is down around four hundredths of a millimetre, thinner than a rolled dough can hold. The layers tear, merge into their neighbours, and you have done an hour of extra work to bake something bready. We stop at three.

Cut and roll. Halve the packet and sheet each half to 3 to 4 mm, around 25 × 60 cm, rested 20 minutes cold so it does not spring back while you measure. Triangles 12 cm at the base and 25 cm tall, alternating point up and point down so nothing is wasted: ten to a strip, twenty out of the packet, about 55 g each. Notch the base, stretch the triangle gently to length, roll from base to tip and finish with the tip tucked underneath.

The proof that catches everyone. 24 to 26 °C, two to two and a half hours. Warm enough to move the yeast and strictly below the temperature at which your butter stops being a solid. A proofer at 30 °C does look faster, and it is: the butter runs out of the layers, pools on the paper, and you bake a dense roll in a puddle of its own structure. Shake the tray at the end — a ready croissant wobbles as one soft mass, and you can see daylight between the layers at the cut face.

The bake. 200 to 220 °C for 18 to 20 minutes. Butter is 16 to 18% water, and at that oven temperature the water in each sheet flashes to steam and drives the dough above it away from the dough below it. The yeast set the volume overnight; the steam sets the structure in the first four minutes.

Cut one open at the bench while it is still warm. The honeycomb — irregular open cells, a spiral you can follow from the outside in — is the record of whether the layers survived the last five hours.

Afterwards#

Weigh the tray paper before and after the bake. Leaked butter is a number, not an impression, and 12 g on the paper tells you more about your proofer than any amount of looking at the croissants does.

Log the temperature of the butter at lock-in and at each of the three folds, the room temperature, the length of each rest, your final sheet thickness, and the proof temperature and time. Change one of those next time, not four.

This bake and weeks 9, 11 and 12 are marked together in bake-off 3: the showpiece, which is worth 50% of the course. It is the hardest thing you will make this semester, and the first attempt is rarely the one you submit.