When you peel away the skin, the firm flesh of the potato is revealed. Its color varies depending on the micronutrients that it contains. Although cream, yellow or purple flesh is common, red, pink or blue is not unheard of. Brown flesh, however, has nothing to do with nutrients and everything to do with enzymes. If your potatoes turn brown after they are peeled, blame it on PPO.
Although the browning that develops on peeled potatoes may look unappetizing, it does not make the potatoes dangerous to eat. The color change is simply an enzymatic reaction and has nothing to do with rot or disease. The browning occurs in all potatoes across the board, but russet varieties tend to have more of a problem than other types of potatoes because they contain less wax.
The PPO -- or polyphenol oxidase -- enzyme is responsible for browning in vegetables and fruits that are cut or peeled. When you remove the peel of a potato, PPO reacts with oxygen in the surrounding air. This reaction can be slowed or stopped altogether by changing the environment. An environment that contains something else for the PPO to react with instead of oxygen eliminates the browning affects.
Stop enzymatic browning in its tracks with a big bowl of cold water. Place the peeled potatoes in the bowl and add just enough water to cover. The water places a barrier between the potatoes and the air, immediately halting the reaction. If you do not plan to use the potatoes within a half hour of peeling, place the bowl in the refrigerator or add ice cubes to the water to keep it from reaching room temperature.
Don’t be alarmed if refrigerated potatoes turn brown during the cooking process. This browning is the result of another reaction that also does not render the potatoes unsafe to eat. After a few hours of exposure to cold temperatures, the starch in potatoes starts to turn to sugar. This sugar caramelizes and begins to darken, giving the cooking potatoes a brown appearance. This carmelization may change the taste of the potatoes.
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