Every time you cut an apple, it is starting to turn brown, and this is because of a chemical reaction. The same is true for other fruits like pears or bananas, which have a tendency to brown once the inner flesh is exposed to air.
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When you cut an apple, its flesh begins to oxidize and turn brown, and this natural reaction is caused by enzymes in the apple known as polyphenol oxidase that react with the oxygen in the air.

What we can do about this and How to Keep Apples from Browning?
1. Use Lemon Juice
Lemon juice is used in preventing apple browning. The citric acid in lemon juice slows down the oxidation process. Here’s how to do it: Squeeze fresh lemon juice into a bowl, then toss the apple slices in the juice or brush it on with a pastry brush.
Also, you can mix lemon juice with water (1 tablespoon of lemon juice per cup of water) and soak the apple slices for a few minutes.
Keep in mind that the lemon juice may slightly alter the flavour of your apples.
2. Soak the Apples in Salt Water
Using saltwater is another way to keep apples looking fresh and not browning because salt acts as an antioxidant and prevents enzymatic browning.
Dissolve 1/2 teaspoon of salt in a cup of cold water, then submerge the apple slices in the saltwater for about 3–5 minutes. Rinse the apples with cold tap water to remove the salty taste.
3. Use Vinegar or Citrus-Based Sodas
Vinegar and citrus-based sodas like Sprite or 7-Up can also slow the browning process. If you use vinegar, dilute 1 tablespoon of apple cider vinegar or white vinegar in 1 cup of water and soak the slices for a few minutes.
When using soda, simply submerge the apple slices directly in the liquid for 3–5 minutes.
Keep in mind that these methods might subtly alter the flavour of the apples.
4. Refrigerate Immediately after slicing
Because temperature plays a significant role in slowing oxidation after treating your apple slices with one of the methods above, store them in an airtight container or plastic bag in the fridge. The cold temperature slows down the enzymes that cause apples browning.
5. Try to Minimize Air Exposure
Because oxidation requires oxygen, minimizing air exposure can help you. Wrap the apple slices tightly in plastic wrap and store them in a resealable plastic bag with the air squeezed out. To squeeze the air out, you can use a vacuum sealer.
If you’re looking for a natural solution with minimal flavour alteration, honey water or saltwater are excellent options, while for a quick fix, use the lemon juice. Don’t forget that cooking apples can also prevent browning, because heat is shutting down the browning process, but this method also softens the apples and give them a cooked flavour.