Cooking often transforms the color of foods, from the browning of bread crust to the rich crimson hue of braised meat. What chemical reactions cause this colorful alchemy? Read on to find out.
Pigments React to Heat, Acids, and Alkalis
Many foods contain natural pigments that impart color. For example:
- Carotenoids – Red, orange, yellow colors in carrots, sweet potatoes, tomatoes
- Anthocyanins – Red, blue, purple colors in berries, red cabbage, grapes
- Chlorophyll – Green color in vegetables
When exposed to heat, acids or alkalis during cooking, these pigments undergo chemical changes that shift their light absorption and alter food color.
Browning Reactions Produce New Pigments
Heating foods triggers browning reactions which create brown polymeric pigments that did not originally exist in the food.
Maillard Browning
The Maillard reaction occurs between amino acids and sugars at high temperatures. This reaction produces brown melanoidin pigments that create the signature golden-brown crust on baked bread.
Caramelization
Caramelization happens when sugars are heated, causing them to break down into brown polymeric compounds. Caramelizing onions or searing meat creates depth of flavor along with color.
Pigment pH Sensitivity Leads to Color Change
Natural pigments are sensitive to pH. Acidic or alkaline environments cause pigment molecules to change shape, altering their light absorption properties.
Anthocyanins
The anthocyanin pigments in foods like red cabbage and blueberries change color based on pH. More acidic conditions make them red, while more alkaline conditions shift them toward purple or blue. Adding acids or bases while cooking blueberries or red cabbage can dramatically change the color.
Green Vegetables
Alkaline conditions cause the green chlorophyll pigment in many vegetables to break down, shifting the color away from green. Adding baking soda to the cooking water of green beans or spinach intensifies this effect.
Cooking Liberates and Creates Pigments
Cooking breaks down plant cell structures, liberating pigments that were not visible in the raw food. Carotenoid pigments are released and become more vibrantly colored when vegetables like carrots are cooked.
Heating also facilitates chemical reactions that generate new pigments. For example, heating onions causes a reaction between amino acids and sugars to produce yellowish-brown quercetin pigments.
Understanding the science of pigments allows chefs to intentionally manipulate the color of food during cooking. Now you can channel your inner food chemist to create visually stunning cuisine!