Guacamole: the Green and the Brown of it

Does burying the stones/pits in your guacamole stop it going brown? Well, no. But it’s kind of fun, and tradition in Mexico dictates that this is the way to go, and who am I to quarrel with tradition – especially of the Mexican variety.

It’s easy to see how the myth came about. You’ve certainly cut an avocado in half, used only one half, and put the other back in the fridge – with the stone still in place – to be used up later. Annoyingly, when you come to use up the second half, the cut flesh has gone an unappetising brownish-black. But wait. When you lift out the stone, you find that the avocado flesh that’s in immediate contact with it has stayed beautifully green. This is what has led people to believe that the stone contains some magical, non-browning properties and that the simple inclusion of the stone(s) will prevent this magnificent Mexican salsa from losing its lustre.

In fact, what stops guacamole going brown – oxidising – is the exclusion of, erm, oxygen, i.e. air. Harold McGee explains it all in his customary engaging and enlightening fashion in his book The Curious Cook. He describes the stone/pit-burying ritual as ‘one of the looniest culinary myths’, and proceeds to debunk it by means of a carefully controlled scientific experiment.

McGee’s experiment went like this. He mashed some avocado into a bowl, buried the stone in the middle and waited to see what happened. After an hour or two, the surface turned an unappetising brown. However, the area immediately in contact with the stone kept its alluring green colour. Next, he made a fresh batch of crushed avocado but instead of burying the stone in it, he used a smooth, shiny, glass light bulb (there’s a great sketch in his book of this unlikely experiment). Once again, the surface of the purée discoloured, but the avocado directly in touch with the light bulb stayed truly green.


The magic, he concluded, lay not in the stone itself but in the fact that air had been excluded. And his recommendation for keeping guacamole bright green, even after a few hours? By all means go ahead and bury the stone in the middle, he says – just for fun and because your Mexican friends have always told you so. But if you want to seriously prevent discolouration, take a piece of clingfilm and press it closely into the surface to exclude any air – note that it’s not enough just to drape the clingfilm over the rim of the bowl or molcajete; it must hug the whole surface of the guacamole.

Try it. It works like a charm and keeps the guacamole brilliantly verdant for several hours, and even overnight. Once you’ve unveiled it, eat it up pronto – not too much of a hardship, given that guacamole is one of the most irresistible foods known to (wo)man.



  • 1 clove garlic, crushed
  • 1/2  teaspoon salt
  • 1 fresh green chile (jalapeno, peperoncino), de-seeded, finely chopped
  • a bunch of fresh coriander/cilantro, chopped
  • 2 ripe avocados
  • juice of 1 lime
  • 3-4 tasty cocktail tomatoes (e.g. Gardener’s Delight), roughly chopped
  • 1-2 spring onions, finely chopped

If you own a molcajete (Mexican pestle and mortar made from rough volcanic stone, pictured here) use this to crush together the garlic, salt, chile and coriander to a fragrant green paste; otherwise, chop (or process) these four together finely.



Cut the avocados in half, remove the stones (reserve them, if only for tradition’s sake) and spoon the flesh out of the skins (or peel skins away).

Mash (or process) the flesh into the garlic/chile/coriander paste using a fork – don’t overdo it, guacamole should not be like baby food but have some texture and character.

guacamole (2)-001

Stir in the lime juice, chopped tomatoes and spring onions (and bury in the stones, if you insist).

guacamole with stone-001

If you’ve used a molcajete, this makes a handsome serving bowl; otherwise transfer the guacamole to a bowl. Press a piece of clingfilm firmly and tightly against the surface to exclude air.

Refrigerate for a while, then serve with tortilla chips, or fresh tortillas straight from the griddle with a sprinkling of crunchy salt, or with grilled fish or poultry. It’s pretty gorgeous with burgers too. Well, pretty much anything…

8 thoughts on “Guacamole: the Green and the Brown of it

    1. I actually remember being wrapped in clingfilm once at a very fancy spa…not sure what it was meant to achieve (maybe stopped me going brown?) but it was fun anyway. Yesss, time to catch up – will call/mail

  1. I still maintain that burying the pit works, but actually guacamole never lasts long enough in my house to find out. Since they have become the new “super food” the price in Mexico has really shot up. Great article.

    1. Yes, it’s a shame the rest of the world has tumbled to the wonders of avocados – do you still buy them by the kilo in Mexico? Here it’s always per piece, and they’ve gone up a lot too

  2. Greetings from Colorado. Thanks for solving the mystery of keeping the guac green. Freshly made it doesn’t usually last long around my house ….but the clinging cling film tip is reason to make larger quantities ! Thanks Sue

    1. Hi Maria, great to hear from you – I know the feeling about guacamole not lasting long (same here) and happy that Harold McGee’s tip will allow you to make even more! Enjoy Colorado, come back and see us soon, we miss you (on the court or off)!!

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