New Scientist - UK (2022-06-11)

11 June 2022 | New Scientist | 51

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These articles are

posted each week at

newscientist.com/maker

What you need
Tangzhong:
3 tbsp milk
3 tbsp water
2 tbsp bread flour

Dough:
300g bread flour
50g sugar
1 tsp salt
7g instant yeast
1 egg
50g butter, melted
100ml milk

STALE bread may seem like it

has simply dried out, but staling

is actually a complex process

that still isn’t fully understood.

In the 19th century, the

French chemist Jean-Baptiste

Boussingault noted that stale

bread can be refreshed by

putting it in the oven, and

showed that bread will still go

stale if it is hermetically sealed

and doesn’t lose any moisture.

In fact, staling is to do with

the chemistry of starch, which is

found in flour and consists of two

kinds of sugar molecules, amylose

and amylopectin. Raw starch has

a rigid, crystalline structure, but

it absorbs water and forms a gel

when cooked.

In the hours and days after a loaf

is baked, this gel-forming process

is reversed: the water slowly

moves back out of the starch

granules and they recrystallise,

making the bread firmer.

If the loaf isn’t very old, the

water remains in the bread and

staling can be reversed by heating

it up again. This is why stale bread

makes perfectly decent toast.

There are plenty of other ways

to make use of stale bread, such

as the Tuscan soup ribollita,

and panzanella, a salad in which

croutons are soaked in dressing.

Bread goes stale most quickly

just above freezing temperature,

so keeping bread in the fridge

isn’t advised unless you plan to

toast it. Commercial loaves will

usually contain added emulsifiers

that inhibit staling, probably by

interfering with the movement

of water out of the starch granules.

The science of why bread goes stale isn’t fully understood. But it

can help us bake a loaf that stays soft for longer, says Sam Wong

The science of cooking

How to bake bread that keeps

Another way to make bread

that stays soft for longer is using

a technique known by the Chinese

name tangzhong, or the Japanese

name yudane. It involves heating

up some of the flour with water to

“pre-gelatinise” the starch before

baking. When heated above 65°C,

starch granules can absorb much

more water and they hold onto

it for longer, even after baking.

This technique is used to make

Japanese milk bread, a soft and

slightly sweet loaf that stays fresh

for several days. The dough used

for this bread is also enriched with

butter, milk and egg. The fats they

provide limit the development of

gluten, which helps give this bread

its tender and fluffy texture.

To make your own milk bread,

start by whisking the tangzhong

ingredients together in a small

saucepan, then place the pan on
a low heat and keep whisking for
3 to 5 minutes until the mixture is
thick. Then whisk in the rest of the
milk, the egg and the melted butter.
In a bowl, combine the flour,
sugar, salt and yeast, then add
the mixture from the pan. Mix it
all together, and knead until you
have a smooth dough that can be
stretched thin. Leave it to rise in a
warm place for 60 to 90 minutes.
Divide the dough into quarters,
then flatten each piece and roll
it into a log. Place the logs, seam
side down, in a greased loaf tin
(12 centimetres by 24 centimetres).
Brush the tops with egg, then bake
The science of cooking at 180°C for 30 minutes. ❚
appears every four weeks

Next week
Stargazing at home

Sam Wong is assistant news
editor and self-appointed
chief gourmand at
New Scientist. Follow
him @samwong1

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