Vol. IX · Fats and Oils Plate 9 of 10fat in dough, shortening, gluten, tender, flaky, shortcrust, pastry, brioche, rubbing in, 酥MT

Fat in Doughs.

Rub butter into flour and the pastry is short and crumbly; leave it in cold flakes and the pastry rises in layers. Same butter, same flour, different place.

In a dough, fat gets between the gluten proteins (VI.10). Coated in fat, glutenin and gliadin cannot meet water and bond into long elastic networks, so the dough stays weak and the baked result is tender. That is the origin of the word shortening: fat "shortens" the gluten strands. Bread uses little or none, brioche a lot (with long kneading to build gluten anyway), shortcrust pastry a lot with very little water or work, so it crumbles.

Where the fat sits matters as much as how much. Rubbed finely into the flour, or melted, it coats as much protein as possible: tender, sandy, short. Cut in as cold pieces the size of peas, it stays separate; in the oven those pieces melt, their water turns to steam and pushes the layers of dough apart: flaky (XXV.6). Chinese 酥皮 uses the same idea by folding a fat-rich dough inside a water dough (XXV.8). The workshop shows gluten development against fat.

Below: gluten development against the fat in a dough for three amounts of kneading and yours, with bread, brioche and shortcrust marked (the course gluten model, a teaching curve).

What you will learn
Workshop
The course gluten model (dough bench): development rises with protein, water above 40 % and kneading, and falls by up to 70 % as fat rises to 40 % of the flour; the way the fat is added scales its effect (melted or oil 1.3, rubbed in 1, cold pieces 0.5). A teaching model of direction and size.

How much, and where

In this model a bread dough with no fat, kneaded ten minutes, reaches 0.71; brioche, with half its flour's weight in butter, reaches only 0.25 even after fifteen minutes of kneading — which is why brioche is kneaded so long and the butter added late, once some gluten has formed. Shortcrust, with as much fat but little water and a minute's work, reaches 0.01: it does not stretch, it breaks, and that is the point.

For a tender, short result — shortbread, tart pastry, scones, Chinese 桃酥 — rub the fat in finely or melt it, keep the water low and handle the dough little. For flaky pastry — pie crust, rough puff, 千层 pastries — keep the fat cold and in pieces, add just enough cold water to bind, and chill between rolls so the pieces never melt into the flour. Oil in a yeast dough makes a softer, finer crumb and keeps bread fresh longer, which is why sandwich loaves and 包子 doughs often contain a little.

At the stove

Make two small batches of the same pastry: rub the butter in finely for one, and leave it in cold pea-sized pieces for the other. Roll, cut and bake both. The first is sandy and short; the second rises in visible layers.

The word "shortening" for solid cooking fat comes from "short" meaning crumbly and easily broken, as in shortbread; the hydrogenated vegetable shortenings of the twentieth century took their name from that job.

Terms

Shortening
Fat used to tenderise doughs by limiting gluten; also a solid vegetable fat.
Short
Crumbly and tender, breaking rather than stretching.
Flaky
In separate thin layers, from pieces of fat melting and steaming apart.
Rubbing in
Working fat into flour with the fingertips until it looks like crumbs.
Fat coats proteins and shortens gluten: worked in finely it makes doughs tender; left in cold pieces it makes them flaky.

Sources

  1. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.
  2. H. McGee, On Food and Cooking: The Science and Lore of the Kitchen, 2nd ed., Scribner, 2004.