Guacamole

Guacamole keeps 1–2 days refrigerated — shorter than most people expect, and the browning starts much sooner than that.

The method that actually works: press plastic wrap directly onto the surface so no air is trapped against the guacamole, then seal the container. Excluding oxygen is the whole game.

A thin layer of water poured over the surface works even better. Pour it off and stir before serving. This sounds odd but is genuinely effective — the water forms a physical oxygen barrier.

Extra lime juice on the surface helps by slowing the enzyme responsible for browning.

Do not leave guacamole out at a party for more than two hours. It contains dairy in many recipes, and in all recipes it is a moist, low-acid food.

Guacamole freezes for about 3 months, though the texture softens. Freeze without dairy or tomato.

Guacamole's famous browning is enzymatic browning, the same reaction that darkens a cut apple or potato. An enzyme called polyphenol oxidase, released when the avocado cells are crushed, reacts with oxygen to produce brown melanin pigments.

Two things are worth being clear about. First, brown guacamole is not spoiled — the discoloration is purely cosmetic, and stirring or scraping off the top layer leaves perfectly good guacamole underneath. Second, the reaction requires oxygen, which is why every effective preservation trick is about excluding air rather than adding anything.

Acid helps because polyphenol oxidase works best near neutral pH and slows considerably in acidic conditions — this is why lime juice is in nearly every recipe, and it is doing chemistry as well as flavoring.

The avocado pit trick is a myth. A pit sitting in the bowl protects only the small area of guacamole directly beneath it, by physically blocking air. It has no chemical effect on the rest.

The real spoilage concerns are the additions: onion, tomato, cilantro, and sometimes sour cream all add moisture and their own contamination risk, and guacamole overall is a moist, mildly acidic food that supports bacterial growth.

Discard on a sour or fermented smell, mold, or a watery separated texture.