The secret to keeping your guacamole green

No one likes brown guacamole.

No one likes brown guacamole.  (iStock)

At Epicurious, we don't spend much time arguing about politics or sports. No, we argue about other things, like guacamole. Should it be chunky? Should it have cilantro? How much lime juice?

But there's one thing we always agree on: guacamole should never, ever be permitted to turn brown.

Browning is simply an avocado’s chemical defense—when something (like a knife) damages the plant’s cells, the avocado releases phenolics that lead to the color change. But brown guacamole is so unappetizing it may as well be poisoned. So I ran a number of tests to find out which trick keeps guacamole bright and green the longest.

I made eight trials and a control, all from one recipe. At first I set the guacamoles in the fridge overnight, but none showed signs of browning. So that was takeaway number one: keeping guacamole cold keeps it green.

But I wanted to take my guacamole testing even farther. So I set the guacs out at room temperature for almost 20 hours. (Note: nobody should eat guacamole that has been at room temperature for this long.) At the end of this testing period, some methods had completely failed to keep the guacamole green, while other methods yielded guac that was as green as the minute it was made. 

Below, a list of the winning and losing methods.

Covering With Water

The idea here is to top the guacamole with a thin layer of water, which keeps oxygen at bay; the water is then tipped off before serving. At the end of testing, this trial showed no browning. But with a result that looks more like gazpacho than chip dip, I still wouldn’t recommend it.

Adding Lime Juice

Absorbic acid (or vitamin C) helps in slowing down browning, so if you’re not opposed to a more lime-heavy guacamole, it seems like a pretty foolproof way to keep things green. I found that a squeeze of lime was enough to create a “float” on top, and that kept the guacamole looking just as bright as it did when I mashed it together. Of course, some folks argue against lime juice in guac. But can they argue with science?

Covering With Oil

Just like the water test, only with grapeseed oil (chosen for its neutral flavor). Lumps in the guacamole that were closer to the surface of the oil turned brown, but for the most part, the guacamole stayed the same bright color. However, much like with the water, I wouldn’t recommend this method because it changes the guacamole’s texture and gives it an oily sheen.

Covering With Plastic Wrap

Food scientist Harold McGee swears by plastic wrap as a way to keep out the oxygen. I can’t argue with McGee—pressing plastic wrap flush against the surface preserved the guacamole and kept it looking green throughout the time it sat out during the daytime. The key is pushing the plastic wrap flush—guacamole preservation is all about minimizing the amount of oxygen in contact with the surface, so even a few inches between the surface and loosely wrapped plastic wrap can make a difference.

What's the absolute best way to keep your gauc green?