Jacoppo Beccaria: in order to understand the composition of flour, he mixed it with water, forming a
dough; then he pressed gently the dough in water, recovering a white powder (starch) and a chewy
Figure 1. When flour is kneaded with water, then pressed in water, a white powder (starch, on
the left) separates from a chewy mass (right) made of some particular proteins (gluten).
This experiment demonstrated that flour was made from starch and gluten. Observing the dough
during the experiments also shows very clearly that gluten is a viscoelastic network where starch
granules are trapped, like fishes in a net (three dimensional). Viscoelastic? It means that gluten has
some elasticity, like rubber, but also that it flows, slowly, with some viscosity.
If butter is added to dough, it divides into particles that are trapped in the same gluten net, and this
dough leads to a robust brisee pastry after cooking.
But if butter is first mixed with flour first (before water is added), then starch granules are coated with
fat, and this fat coating hinders gluten formation, so that sablee pastry is made.
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Figure 2. There are two ways of mixing wheat flour, water and butter (top): if flour is kneaded
first with water, a gluten network is formed, into which fat is dispersed, and a “brisee” pastry is
obtained (left) ; but if the flour is first mixed with butter, no gluten network can form when
water is added (right), and “sablee” pastry is formed. How much starch can be put into butter?
A model where starch granules are considered as disks that form a regular tiling leads to a
proportion of 1 part of butter for 3 parts of starch. When a 3-dimensional model is preferred, a
1/1 proportion is calculated.
Let’s now come to the proportion of the various ingredients in dough. A small calculation can be made
to understand how much flour can be mixed with a certain quantity of butter. Let’s consider first the
two dimensional case of a square packing of circular flour granules having all the same radius.