Cut potatoes turn brown when they’re exposed to oxygen. This reaction isn’t harmful, and it doesn’t affect the taste, but it can make the potatoes appear less appetizing. To prevent this color change, soak the potatoes in a bowl of cold water mixed with vinegar or lemon juice.
Why Potatoes Turn Brown When Sliced
When you slice a potato, you cut through the walls of the cells, which contain an enzyme that reacts with oxygen in a process called oxidation. This reaction is similar to what happens when iron rusts after prolonged exposure to oxygen and water. When foods such as potatoes, apples, and avocados oxidize, they initially turn brown. After a while, the cell walls begin to break down, and the food becomes soft.
Prevent Oxidation in Cut Potatoes
The only way to prevent oxidation is to slow down the chemical reaction between the enzymes and the oxygen in the air. This is how you do it:
- Reduce the amount of air the potato is exposed to.
- Lower the temperature of the potato.
- Reduce the pH of the potato.
None of these methods permanently prevent oxidization, but they slow it down, giving you enough time to cook the potatoes, which ultimately destroys the enzymes an any possibility of browning.
Prepare Sliced Potatoes to Prevent Browning
Before you cut the potatoes, set a large bowl of ice water nearby. Add a splash of lemon juice or vinegar and stir to combine.
As you cut the potatoes, immediately submerge them in the bowl of acidic ice water. This slows down the enzymatic reaction by keeping them cold, lowering their pH, and coating them with water, which reduces the amount of oxygen exposure.
Cook Soaked Potatoes
If you plan to make mashed or boiled potatoes, transfer the cut potatoes directly from the ice water into the cooking water. Don’t worry about the small amount of extra liquid and residual acid on the potatoes—these don’t alter the final dish.
To make homemade potato chips or any type of crispy potatoes, follow one extra step:
After soaking cut potatoes, spread out two or three layers of paper towels. Lay the sliced potatoes on the paper towels in a single layer, then cover them with another two layers of paper towels. Press gently to dry the potatoes. Repeat until you’ve soaked up most of the extra moisture; then continue with your recipe.