While a brown top-layer on your guacamole is totally safe, if the dip has been open for more than three days, it might be best to toss it (particularly if more than the top layer has changed color).

You can safely eat an avocado or guacamole that has turned brown due to oxidation, just as you could eat an apple that has undergone the same chemical reaction.

However, the flavor of brown guac may not be exactly the same as a fresh batch. “Brown guacamole may taste slightly bitter due to oxidation,” says Alsing. However, for most people, the difference ...