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How to Stop Guacamole from Turning Black

I have heard that to stop guacamole from turning black that you should save the avocado pit and put it on top of the guacamole once it is made.  How does this work?



This tip works only if the avocado pit is big enough to completely cover the bowl from edge to edge.  What it does is exclude oxygen.  Once the avocado fruit has been cut and the contents mashed, an enzyme released from inside the cells of the avocado flesh starts causing the pulp to turn brown in the presence of oxygen.  Placing the pit on top of the guacamole keeps oxygen away from the area directly in contact with the pit.  The surrounding area not covered by the pit still turns brown.

Any oxygen impermeable barrier will stop browning from happening; an avocado pit, plastic wrap, as Harold McGee found in The Curious Cook: More Kitchen Science and Lore, even a 40 watt light bulb (not recommended).  While McGee found that all plastic wraps worked to some degree, Saran Wrap, which allows less oxygen to pass through it than some other brands, was most effective.  Whatever material is used, it should be pressed gently down onto the surface of the guacamole to remove as much oxygen as possible.

The citric acid in the lime juice used to make guacamole also helps a bit, but to be completely effective it would need to be used in much larger amounts than most recipes call for.

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I have found that plastic or cling wrap works fine if the container isn't disturbed. It is easy, however for a small opening or tear to allow air to seep beneath the plastic causing part or all of the surface to turn. What has worked for me is a slight embellishment on the method described already. I put the guacamole into a Tupperware-like container (preferably square, but not necessary) and cover it with plastic wrap so that it is contact with the surface of the guac and tamped down to remove as much air as possible. The excess wrap hangs over the top edge of the container. Then I lay two or more slices of a soft bread (the pure white tasteless fluff is cheap and works well for this) until it is just higher than the top of the container. I press the lid down onto the bread and snap it closed. The soft white bread is easy to mold for any shape container. Although guacamole doesn't sit around much longer than the day after it was made in my house, I'm sure this method will extend the shelf life of leftover guac a couple of days longer than usual.

That salsa idea sounds great. I usually mix some in but putting it on top to stop the browning seems obviously brilliant.

With the same idea of sealing out the oxygen from the top of the bowl of Guacamole...flatten the guacamole and put a thin layer of salsa on top so you can't see anymore green. You can either mix the salsa into the guacamole when you're ready to eat it or just scoop it up with a chip.

When I make guacamole I omit the lime juice from the recipe initially. Then once the avocados and all other ingredients are completely mixed I place them in a bowl and firmly smooth the top very evenly. Then I gently pour enough lime juice over the top to completely cover the avocado mixture. This seals the mixture and keeps it from going brown. It can be stored in the fridge for a few hours until guests arrive. When I am ready to serve I pour off ALL the lime juice as it is way too much for the guacamole and then mix. The residual lime juice is just the right amount to flavour the guacamole without making it sour and nothing turned brown.

Yes, I find McGee is wonderful for clearing up all sorts of misconceptions. My copy of his book is well-tumbed, indeed.

And, by the way, I find the best way to keep guacamole from discoloring is to invite a lot of people over and eat it up. Of course, that advice works with all edibles.


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