You cut an avocado at noon, use half, and come back at dinner to a brown mess. It happens to everybody. The good news is that browning is mostly about air, not time, and there are a couple of easy ways to slow it down.

Why It Turns Brown

When you slice an avocado, you break open cells that were sealed up. Enzymes inside react with oxygen in the air and the flesh darkens. It is not spoiling. It is oxidizing, the same way an apple slice does. Cold slows that reaction way down, and so does cutting off the air supply.

The Method I Actually Use

Leave the pit in if you only used half. It does not stop browning on its own, but it blocks air from the hollow it sits in, and that is where the worst browning starts.

1. Rub the exposed flesh with a little lemon or lime juice. The acid slows the enzyme reaction.
2. Press plastic wrap directly onto the surface. Not over the bowl. On the avocado.
3. Put it in an airtight container and refrigerate.

The plastic wrap trick is the one that matters most. I used to cover the whole bowl and wonder why the top still turned. The wrap has to touch the flesh so no air pocket is left.

If You Are Making Guacamole

Guac is harder because it is all exposed surface. Press a sheet of plastic wrap flat onto the top and push out the air bubbles. Some people float a thin layer of water on top and pour it off later. That works too, though it waters down the edges a touch.

One thing I got wrong for years: I kept half avocados on the counter. They never lasted. Now they go straight in the fridge and I get two or three good days out of them, sometimes more.