No doubt you’re making all sorts of potato dishes this winter, like my favorite potato and spinach au gratin or this tartiflette. Or it’s holiday time and you’re figuring out how to prep mashed potatoes for a crowd while keeping them pretty. Potatoes, like artichokes, turn brown pretty fast once you’ve peeled them and they’re exposed to air. But you can keep your dishes photo-op worthy by following these tips to keep your cut and peeled potatoes from turning brown.
First though, a short primer on browning, courtesy Harold McGee’s excellent reference book On Food and Cooking. Foods turn brown in one of two general ways. Non-enzymatic browning happens when foods are exposed to heat. These are the reactions that give cooked meat and bread their golden-brown colors and deepened flavors. Then there is enzymatic browning – not so great. That’s the browning that happens when food is exposed to air, like after you peel or slice a potato and it turns brown. It doesn’t affect the taste, only the presentation.
Chemistry of enzymatic browning
Science is fascinating to me, so just follow me for a minute. Enzymatic browning happens on the cellular level in fruits and vegetables. Colorless phenolic compounds, also called phenols, are stored in the vacuoles of plant cells. Enzymes are found in the cytoplasm. In a piece of uncut or undamaged produce, these molecules do not come into contact with each other. But once the cell is damaged, phenols come into contact with enzymes as oxygen is introduced. Enzymatic browning happens when oxygen allows the enzymes to bind phenols into new light-absorbing molecules that discolor the area.
Prevent browning with lemon juice
Enzymes are a type of protein made up of chains of amino acids. The bonds between those amino acids are sensitive to pH; highly acid or alkaline substances break down the amino acid bonds, slowing down or stopping the enzymatic activity. This is why lemon juice, is a common kitchen ingredient with a low pH, is often used to prevent browning. Immediately upon peeling or slicing, drop potatoes in a mixture of 3/4 cup lemon juice and 1 gallon water. Drain before cooking.
Prevent browning with cold water
You can use cold water alone to prevent browning. This works in two ways: enzymatic activity slows down in temperatures below 40 degrees Fahrenheit, and the presence of water limits available oxygen. Just immerse potatoes in ice water immediately after peeling or slicing. Drain before cooking.
Prevent browning with heat
Boiling temperatures also destroy the enzyme that causes browning, so by blanching or parboiling your peeled or sliced potatoes you’ll will preserve their color. Drop prepared potatoes into rapidly boiling, salted water. Boil for 2 to 3 minutes. When removing from boiling water, place potatoes immediately plunge into icy water to prevent further cooking. When the potatoes are cool, drain and store until ready to cook.