Few people know that the avocado is an ecological anachronism, that it most likely evolved specifically to entice the tastes and the large gullet of the now-extinct giant ground sloth.
Another fun piece of avocado trivia: The name of the tropical fruit can be traced all the way back to the ancient Aztec word for "testicle." But with Super Bowl 46 less than a month away, the finer points of the alligator pear, as the avocado is also known, will soon be obscured by the fact that you can smash one up and dip chips in it.
As Americans prepare to pulverize avocados by the millions on game day, they face a problem as old as guacamole itself: how to keep it from going brown. After all, guacamole's color is so singular in the realm of foodstuffs that the dip’s ultimate virtue seems to live and die by its vibrancy.
Many aficionados promote a time-tested approach to this problem: adding the whole avocado pit to the guacamole to help stanch the browning.
Science actually supports this method, but not for the reasons you might expect.
Like many other fruits that brown rapidly, such as apples and bananas, avocados contain a common culprit in their chemical makeup, an enzyme called polyphenol oxidase (PPO). When you cut open the fruit, you also crack open its cells, which allows the PPOs to react with oxygen in the air. This chemical reaction reshapes the phenolic compounds in the fruit’s tissue into a repeating chain of molecules, or a polymer, with a brownish pigment. In laymen's terms, this oxygen-driven polymerization could be pretty accurately described as fruit rust. [Fast Food Nation: Americans Cook Order Out More than Any Other Developed Country]
So how does leaving the pits in the bowl mitigate this process? It is not because the pits exude an ineffable, protective aura that reminds the guacamole where it came from, or because they emit chemicals that counteract the oxidation process. As anyone who’s tried the method can attest, the pits are really effective at preventing browning only on the part of the guacamole’s surface they touch.
The pit protects the guac simply because it shields a portion of the dip’s surface from exposure to air. You'd be just as well off plopping a few hardboiled eggs or some golf balls or an iPhone into your guacamole.
Recommending that someone leave the pits in a bowl of guacamole to prevent browning is a bit like recommending that people cover their heads tightly with their hands to prevent their hair from getting wet in a rainstorm. It would help, but not as much as an umbrella. For guacamole, the best umbrella seems to be plastic wrap tamped down snugly to the surface of the dip, to limit as much oxygen exposure as possible.
If you prefer to attack the enzyme instead of the air, adding lemon or lime juice – ingredients many guacamole recipes already call for – also will delay browning. The citrus fruits’ relatively high acidity, along with their natural antioxidants and high vitamin C content, helps handicap PPO-driven oxidation.
Better yet, use lemon juice, avocado pits and plastic wrap. Or just eat it really quickly.