I needed only half an avocado for a recipe. I spritzed the remaining half with lime juice and wrapped it in plastic wrap. When I went to use it two days later, it was brown. Is there an effective way to save unused avocado, or should I have just eaten it all in one sitting?

I’m surprised you were able to abstain from eating half an avocado; I can’t.

There are many methods which claim to keep avocado halves or guacamole from oxidizing. I have yet to find one that I’d consider successful. But I’ll tell you the most common ones if you want to do some experimentation. People’s expectations as to the results they’re happy with differ, and I’m probably pickier than most. It also depends on how long you expect the avocado to stay green. Two days is optimistic.

All methods are based on excluding air from the surface of the avocado. You’ve tried the acid method and combined it with the plastic wrap method, so we can skip those. Although I’ll add that first, spritzing isn’t a very effective way to coat the surface, and second, even under plastic wrap, lime juice will evaporate and the wrap isn’t airtight. What other methods are there? (Please refrigerate the leftovers whichever method you try.)

You can leave the pit in the avocado, and this works well… for the portion which is in direct contact with the pit. The rest will turn brown. You can remove the pit and place the fruit (yes, avocado is a fruit), cut side down on a flat plate and cover it with plastic wrap. Some swear that a coating of cooking spray or a film of oil works. True that these won’t evaporate, but the complete surface must be covered, and you may not want oil next time you use it. Have fun scraping it off if that’s not what you want.

The latest idea I ran across not too long ago came from some of my personal chef friends. Cut up the avocado, put it (or guacamole) in a glass jar, and add a half-inch layer of water to cover; refrigerate. Pour it off before using either one. I guess this works okay if you’re not going to leave it long, but when I tried it, the avocado softened and it seemed like the flavor had washed out. And trying to pour the water off while keeping the guacamole in the jar would be an interesting challenge; I didn’t try it with that.

My recommendation is to just add the rest of the avocado to the recipe, or use any of these methods and eat it up within a day. Even the Hass Avocado Board doesn’t advocate keeping a cut avocado longer than that.