Ever wonder why a beautifully green avocado turns an unappetising grey within an hour of being cut?
The culprit is polyphenol oxidase — an enzyme that lives quietly in avocado flesh until your knife exposes it to oxygen. The moment that happens, oxidation kicks off and the surface darkens. It's the same reaction that browns a sliced apple, and knowing that tells us exactly how to fight it.
Three things that actually work
1. Acid, fast
Lime or lemon juice lowers the pH around the exposed flesh, and polyphenol oxidase is far less active in acidic conditions. Brush it on as soon as you cut — within two minutes, not ten. Half a teaspoon covers a whole avocado half. Lemon works just as well as lime.
2. Press cling film flush to the surface
Air is the enemy. If there's no gap between the film and the flesh, the enzyme has nothing to react with. Press firmly so there are no air pockets at all — not just draped loosely over the top of a bowl. It makes a real difference.
3. Keep the stone in the unused half
The stone doesn't magically prevent browning everywhere, but the flesh directly under it stays greener longer simply because it's shielded. Pair this with the cling-film trick and the half will look decent the next morning.
What doesn't work
Water. Submerging avocado halves in water circulates as a hack every year. It does slow browning somewhat, but it also waterloggs the flesh and softens the texture. Not worth it.
Olive oil. Oil on the surface limits airflow, but the avocado absorbs a noticeable oiliness. Fine if it's going into a salad dressing anyway; less ideal if you want clean, fresh flavour.
The honest answer
None of these tricks stop browning entirely — they slow it. Even with acid and cling film pressed flush, the flesh will start to turn after 12–18 hours. The best strategy is to cut only what you need and store the rest uncut. A whole, uncut avocado in the fridge keeps for two to three days without any oxidation at all.
