It's the pits when vibrant green guacamole turns into an unappetizing brown mush. Placing the avocado pit in the dip is a common folk remedy advised for preventing browning, but it actually does very little to stop this completely natural process. Fortunately, it's still possible to slow guacamole browning, and with no pits required.
The Myth of the Pit
Guacamole turns brown because the enzyme polyphenol oxidase reacts with air, causing the avocado to begin turning brown on contact. An avocado pit doesn't prevent this enzyme from oxidizing, so any guacamole exposed to air will still continue to brown. The pit may give the illusion that it's preventing the color change, but that's only because air isn't in contact with any of the guacamole beneath the pit.
Avoid the Common Pitfall
If the enemy is air, and a pit can block some of that air, it may still seem like a good idea to toss the pit into the guacamole. Unfortunately, this may do more harm than good. An airtight seal provides the best defense against browning. A large avocado pit, protruding above the surrounding guacamole, can prevent an airtight seal. Although the guacamole beneath the pit remains a pleasing bright green, the guacamole exposed outside the pit may brown more quickly.
Keep It Under Wraps
Toss the pit and use plastic food wrap instead. Pressing the plastic onto the top of the dip during storage prevents air contact over the entire surface, so no browning can occur. To further prevent air exposure, cover the container with a tight-fitting lid. Safely keep the dip in the refrigerator at 40 degrees Fahrenheit or less for up to two days without any browning.
Stay in the Green
Although a tight cover prevents browning during storage, once you set the dip out and peel back the cover the enzyme action begins. Mixing an acid into the guacamole when you make it slows oxidation and browning, without the need for a pit or a piece of plastic wrap ruining the presentation. Mix a teaspoon of lemon or lime juice into the dip when you make it, then sprinkle the surface with more juice before setting it out.
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