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Prevent cut potatoes from turning brown by soaking them in a bowl of cold water mixed with vinegar or lemon juice. This will prevent the chemical reaction that results when potatoes are exposed to oxygen, which causes browning. Brown potatoes aren't harmful, and the browning doesn't alter the taste, but it can make the potatoes appear less appetizing.

Why Potatoes Turn Brown When Sliced

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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 oxidization. This reaction is similar to what occurs when iron reacts with oxygen and water to produce rust. When foods such as potatoes, apples and other produce oxidize, they initially turn brown. After a while, the cell walls begin to break down, and the food turns soft.

Prevent Oxidation in Cut Potatoes

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The only way to prevent oxidation is to slow down the chemical reaction between the enzymes and the oxygen in the air. Accomplish this using one of several methods:

  • Reduce the amount of air available
  • Lower the temperature
  • Reduce the pH of the food

None of these methods permanently prevent oxidization, but they will slow it down, giving you enough time to cook your potatoes. Cooking the potatoes destroys the enzymes, preventing the potatoes from browning.

Prepare Sliced Potatoes to Prevent Browning

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Before you begin to cut your 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 will slow down the enzymatic reaction by keeping them cold, lowering their pH, and coating them with water, which reduces the amount of oxygen available to the reaction.

Cook Soaked Potatoes

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If you plan to make mashed or boiled potatoes, transfer the cut potatoes directly from the ice water into the cooking water. The small amount of extra liquid and acid that remains on the potatoes will not alter the final dish.

To make homemade potato chips or some other recipe that calls for crispy potatoes, follow one extra step:

Spread out two or three layers of paper towels; then lay the sliced potatoes on the paper towels in a single layer. Cover them with another two layers of paper towels, and press gently to dry them. Repeat this until you have soaked up most of the extra moisture from the potatoes; then continue with your recipe.