To avoid all of the downsides that come with using a metal knife to slice an avocado and keep your avocados green as long as possible, opt for a ceramic or plastic-bladed knife.

When you use a metal knife to slice a ripe avocado, the copper and/or iron in the knife’s blade reacts with the polyphenol oxidase enzymes in the avocado's flesh.

That reaction, in turn, speeds up a naturally occurring process called oxidation, resulting in unpleasant browning and deterioration of some of the avocado’s flavors.

While avocados will brown regardless of what type of knife you use or how well you try to preserve them, metal knives speed up the inevitable.