The most effective way to keep cut fruit from browning is to bring the cut surface into contact with lemon juice, vinegar water or lightly salted water right away. That acidic or salty environment slows down the reaction responsible for browning.
Fruits like apples, pears, bananas, avocados and peaches turn brown within a few minutes of hitting the air; this shift doesn't mean the fruit has spoiled, it simply signals a chemical reaction on the surface.
Why does fruit turn brown?
When a fruit's cells are cut open, an enzyme that normally stays in a separate compartment meets phenolic compounds and reacts with oxygen in the air. That reaction produces brownish compounds on the surface — in kitchen terms, this is called enzymatic browning.
In fruits like apples and pears this enzyme is quite active, so the colour change becomes noticeable within 5-10 minutes of cutting. In acidic fruits such as citrus and strawberries, the same enzyme is far less effective, so browning progresses much more slowly.
How do you apply the lemon-juice and salt-water method?
Cut fruit is placed in a bowl, drizzled with a few drops of lemon juice and gently tossed; the acid in lemon disrupts the conditions that browning needs to occur. The same effect can be achieved by dipping the fruit for a few minutes in lightly salted water, made with about a teaspoon of salt per cup of water.
With the salt-water method, fruit shouldn't sit for more than 3-5 minutes before being drained and lightly rinsed, or it can pick up a faint salty taste. With lemon juice, the amount should stay small, or it can overpower the fruit's own flavour.
Which fruits brown fastest?
Apples, pears, bananas and avocados are among the fastest to brown and need treating right after cutting. Peaches and nectarines brown quickly too, especially when left in a warm spot.
Strawberries, grapes, watermelon and citrus, on the other hand, hold their colour for a long time even at room temperature thanks to their naturally high acidity, and usually don't need any extra treatment. Pears brown a little slower than apples but still fall into the fast-browning group.
Other ways to prevent browning
Storing cut fruit in a tightly sealed container also slows browning, since it limits the oxygen available for the reaction. Pressing a thin layer of cling film directly onto the surface of the fruit has the same effect.
Keeping fruit cold in the fridge slows the reaction but doesn't stop it completely; for the best result, cutting should be left as close to serving time as possible.
Does browning matter for fruit that will be cooked?
For fruit that will be cooked anyway — for compote, jam or a tart filling — a few minutes of browning barely matters, since heat is going to change the fruit's colour and texture regardless. That's why fruit destined for the pot can go straight in after cutting instead of into lemon water first.
Browning usually isn't an issue when juicing fruit either, since juicing breaks the fruit down into liquid and changes its colour anyway. Browning really only matters when fruit will be served raw and visible — on fruit platters, in salads, or as a pastry garnish.