Brown guacamole is not spoiled. It is oxidized. The same reaction that turns a cut apple brown is working on your avocado.

You cannot stop oxygen entirely. You can slow it down, and the difference between a good and a bad method is whether air actually touches the surface.

What fails

I have tried all of them. A lemon wedge sitting on top does almost nothing. Pressing plastic wrap over the bowl helps only if it truly touches the guac with zero air pockets, and in a round bowl that is harder than it sounds.

Leaving the pit in is folklore. The pit protects the avocado underneath it. The rest of the bowl browns anyway.

What works

Press the guacamole flat, then pour a half inch of water over the top. Sounds wrong. It is not. Water pushes all the air away, the guac stays green, and you pour the water off before serving.

People look at me sideways when they see a bowl of guac with water on top. Then they taste it the next day and stop asking questions.

Second best option is a container that is barely bigger than the dip. Less headspace means less air, which is really the entire game. A tall narrow container beats a wide shallow one every time.

Acid matters too

Lime juice is not just flavor. The acid slows the browning reaction, so a generous squeeze buys you a few hours even in an imperfect container.

Two limes for four avocados is about right. More than that and the guac turns sour and thin.

Reviving a browned batch

If only the top layer went brown, scrape it off with a spoon and stir the green underneath. Nobody will know.

If it is brown all the way through, the texture has gone slimy too. Start over. Guacamole is cheap and disappointment at a party is not.

Make it the same day if you can. All of these methods buy hours, not days.