This easy trick is courtesy from the women’s health magazine. Just cut a red onion into fairly large chunks into an airtight plastic container, and place the avocado half (with the pit) on top. The skin should be touching the onion chunks.
Put the lid on the plastic container, throw it in the fridge, and brown avocados will be a thing of past. How does the trick work? The onion emits sulfur gases, which help stop the oxidation process that turns avocados brown. Here’s a video that details the trick, courtesy of Chow, an online resource for recipe demos and cooking tips: