This is excerpted from our newest cookbook, All About Eggs, an encyclopedic ovarian overview and the only tome you need to own about the indispensable egg.
A deeply colored yolk is beautiful to behold and reflect on, but it doesn’t really tell you anything about how the hen was raised, or how flavorful or nutritious the egg is. Sorry. It’s true that uncaged farm hens and backyard hens accumulate yellow-orange pigments from green plants and maybe from bugs that battery hens don’t. But feeds for battery hens routinely include ingredients for coloring their yolks that are rich in the same—or similar—pigments related to vitamin A (mainly lutein and zeaxanthin, both important for keeping our eyes healthy). Among those ingredients are yellow maize, meals made from marigold petals, alfalfa, grass, or algae, paprika extract, and (in Europe, not the United States) synthetic pigments.
Egg producers in different regions formulate their feeds to match consumer preferences, which are measured on scales like the Roche Yolk Color Fan (there are similar color scales for salmon flesh). According to a recent European review, Ireland and Sweden prefer light yellow yolks of Roche 8–9, France and England a deeper 11–12, and northern Europe and Spain an orange 13–14. A number of other factors also affect yolk color, including the hen’s breed, age, and other feed components. So the only way to know where a beautiful yolk got its color is to know the hen’s owner and ask what it eats.
The best way to highlight yolk color is to avoid cooking the egg fully. Just as happens in the white, the heated proteins form microscopic aggregates that scatter light rays and eventually turn the liquid into a cloudy solid. The more moist you leave the yolk, the clearer and deeper its color will remain. —Harold McGee
When fed to chickens, the following have been proven to produce more deeply orange yolks.
— Marigold petals
— Lucantin® (industry-manufactured carotenoid supplement)
— Olive leaf
— Fish oil
— Orange maize (maize fortified with β-cryptoxanthin)
— Foods naturally high in β-cryptoxanthin including red peppers, pumpkin, butternut squash, paprika, chili pepper, persimmon, tangerine, cayenne/red pepper, papaya, cilantro
— Foods naturally high in lutein: maize, kiwi, red grapes, zucchini, pumpkin, spinach, yellow squash, cucumber, pea, green pepper, butternut squash, celery, green grapes, brussels sprouts, scallions, green beans, broccoli, apple, collard greens, turnips
— Sunflower seeds
— Rapeseed/full-fat canola seed
— Amino acids (aka protein, found in meat, milk, fish, eggs, soy, beans, legumes, nuts, wheat germ, quinoa)
— Gynura procumbens (longevity spinach)
— Red peppers: cayenne, chili, hot pepper, red chili, spur pepper, tabasco pepper, cherry peppers, cone peppers, paprika, sweet peppers
— Leaves: moringa, mangrove, and calliandra
— Distillers dried grains (byproduct of ethanol industry)
— Karaya saponin (from three different tree species found in Indian and Africa)
— Vitamin C
— Carrots, especially PURPLE carrots
— Spice mixture (cardamom, cumin, hot, and black pepper)
— Blue mussels
— Hazelnut oil
— Dehydrated turf grass
— Annatto seeds