Then, keep aside one “control” slice, number 1.
To slice number 2, add some lemon juice.
We know that lemon juice contains some water. Would water be enough to prevent browning? On
slice number 3, add just some water.
But we also know that lemon juice is “acidic”. Is acidity responsible for the effect against browning?
On slice number 4, let’s add some clear vinegar.
Lemon juice also contains vitamin C, which chemists call “ascorbic acid”. You can get some at the
chemist. Add some of this to slice number 5.
Then wait and compare the browning of the slices: as ascorbic acid is clearly very efficient, why keep
using lemon juice instead?
We all know that wheat flour is made from wheat. When wheat is processed, a powder is formed: this
is flour. What is it? In 1754, the Italian chemist Jacoppo Beccari used the classic method of chemical
analysis to find it out.
Chemical analysis, in principle, is always the same: when you want to know more about some
material, you divide it into two simpler parts; then you take each of these parts, and you divide them
again, and again, and again…and finally you know which molecules composed the original material.
In the case of flour, you can easily carry out the Beccari experiment by yourself:
Take about 100 g of flour, and add a teaspoon of water. Mix, add more water, mix again, and repeat
until obtaining dough.
Work this dough until it becomes very hard, and while kneading, observe the material that you work
with. You cannot see the grains any longer, but some “elastic threads” appear.
More precisely, the dough is “viscoelastic”: it means that when you stretch it, there is some elasticity
(like rubber - it reforms its shape after being released), and this elasticity is not total and there is some
slow flow (viscosity).
II - 5 (of 9)
When the dough is formed (remember that it is only made of flour and water), put it in a large vessel,
and knead – mix it slowly. You can see a white powder that escapes and settles at the bottom, and
you are left with a yellow material.
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