Why You Should Avoid Using A Metal Knife To Slice Avocados

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If you love avocados you will be aware of the ridiculously short window of perfect ripeness they have; 30 minutes is the average time before they turn to a gloopy, brown mess. But if you manage to time it just right and get your avocado out of its skin at the peak of its green, buttery goodness, you may want to steer clear of using a metal knife to do it, which could potentially encourage the fruit to brown.

If you are planning to scoff your avocado in one sitting (and who could blame you?), there is no real reason to think too much about oxidation. But if you are eating half and storing the rest for later, preventing browning should be a priority. Avocados go brown pretty easily once they have been cut, so even a small increase in the speed at which that happens will be detrimental to your future avocado happiness.

Not all metal knives are a threat to your precious avocados, thankfully. Modern stainless steel knives contain chromium, which forms a protective layer that should prevent the blade having an effect. The most likely issue comes from a different type of steel — carbon steel — the knives of which are made from the same iron and carbon, but without the chromium contained in the stainless version.

Once you slice open an avocado, you send it on a slippery oxidation slope toward brown, mushy disappointment. One of the enzymes in avocados, called polyphenol oxidase, uses the oxygen in the air to speed up the oxidation of phenols within the avocado, ruining its appealing appearance. This is the same compound that causes bananas to turn brown as they ripen.

The presence of iron or copper can interact with food phenols and take part in oxidation reactions, which is where the switching of knives comes in. If iron ions make their way onto the avocado as you slice it in half, there is a chance that the browning may speed up slightly. Since avocado browns quickly, any measures that can be taken to slow down, or at least not speed up, the oxidation process should be attempted. A ceramic knife blade is chemically inert and will not introduce iron ions into the process, removing the concern of increased oxidation from the knife.

Other ways to reduce the browning of avocados include squeezing acid such as lemon juice across the cut half, keeping the stone in place to protect the flesh underneath, and keeping it in an airtight container until you have your next avocado craving.