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Experimentbeginnerdraft

Why does the apple turn brown?

Also searched as: brown apple experiment, lemon and apple

In short: Apple slices turn brown in the air, unless you protect them.

Picture it

Like a bike rusting in the open air: oxygen discolours the exposed surface, and a protective film prevents it.

Before · Afterfreshly cut
in the air
with lemon
in water
Schematic
You need · 30 minutes
  • an apple
  • lemon juice
  • a glass of water
  • three plates

How it’s done

Sequence · Step 1 of 3
123

Cut an apple into slices.

All steps as a list
  1. Cut an apple into slices.
  2. Drizzle one slice with lemon juice, put one in water and leave one as it is.
  3. Compare after 30 minutes.

What you see

The untreated slice is brown; the other two stay pale.

Why it happens

An in the apple reacts with the oxygen in the air and forms brown pigments. slows the enzyme down; water keeps the air away.

Related entries
Enzymatic browningBircher muesli
Sources · 1
  • Harold McGee: On Food and Cooking (2004)