HOW TO KEEP AVOCADO FROM TURNING BROWN

LEAVE THE AVOCADO PIT IN

Most fruits and vegetables change color when their flesh is exposed to the air due to oxidation--that is, reaction with oxygen in the air. Some fruits and vegetables, such as the avocado, are more susceptible than others because they contain an enzyme called polyphenol oxidase. This enzyme works on phenolic compounds in the flesh of the avocado, changing their chemical structure and thus their color.

So there are two culprits in this browning process--the enzyme in the avocado, and the oxygen in the air. Logic suggests that if the avocado pits prevents browning, one of two things must be happening: Either the avocado pit chemically changes the guacamole, or it prevents oxygen from getting to the guacamole in the first place

REFRIGERATION OR BOILING

You can attack the other culprit, the enzyme, in a couple of ways. Refrigeration will slow down the action of the enzyme, but the whole fruit should not be refrigerated at very low temperatures, as the avocado is very susceptible to chilling injury. Boiling can also be used to slow down or stop the enzyme action, but I don't advise boiling your guacamole--for one thing, the tannins in it are reportedly bitter when cooked.

LEMON OR LIME JUICE

Since the enzyme doesn't like acidic conditions, adding something acidic to the guacamole such as lime or lemon juice will slow the reaction of the enzyme with oxygen. Both lime and lemon juice have pH values that are fairly acidic, being between pH 2.0 and 3.0, so choose whichever better suits your recipe. Ascorbic acid (vitamin C) will also help to slow down oxidation (note 1), and since lemon and lime juice both contain large amounts of it, they seem ideally suited for guacamole, which might explain why they appear in many guacamole recipes.