Unexpected egg yolks aren’t just in the pages of Dr. Seuss books. Though you probably won’t encounter green eggs and ham anytime soon (but it’s possible), yolk colours can vary from the palest yellow to reddish brown. What affects the colour of egg yolks? Why are some darker than others, and are intensely pigmented yolks healthier? Poultry experts from across Canada explain.
What determines egg yolk colour?
Unlike shell colour, which depends on the breed of chicken, the hue of an egg yolk is determined by the hen’s diet.
Yolk colour ranges by region and country with variations in feed ingredients, says Stuart Smyth, an agricultural professor at the University of Saskatchewan. But it largely depends on carotenoids — the pigments that give foods such as carrots and corn their colour. “If they happen to eat carrot peelings or something like that, chickens’ bodies can’t process carotenoids, so it goes right into the egg, making the yolks darker.”
Pigments accumulate in the yolk because many are lipophilic, meaning they’re soluble in fats, says Grégoy Bédécarrats, professor and acting chair of the University of Guelph’s Department of Animal Biosciences. “The yolk is the lipid content of the egg.”
Yolk colour can vary so much that it can be shocking to experience eggs in other parts of the world. Bruce Rathgeber, associate professor and chair of Dalhousie University’s Department of Animal Science and Aquaculture, recalls a hard-boiled egg he ate for breakfast on his first trip to the Netherlands. It was salmon pink, which surprised him then, but he ended up creating a similar effect as part of research projects on local waste feed ingredients back in Nova Scotia.
The chickens incorporated astaxanthin — the carotenoid pigment that gives salmon their pink-red colour — from crab and lobster meal into their yolks. The result was “mandarin orange peel, or maybe even blood-orange red,” says Rathgeber. “They were quite dramatic.”
Rathgeber gave the first dozen eggs to a friend for feedback. “His mother-in-law came for the weekend, decided she’d make breakfast before everyone woke up, and started cracking open the eggs and threw every one of them out,” he says, laughing. “Because she thought, ‘How could they possibly be this colour?’” When they sold the eggs on campus, they included instructions on what to expect to prevent confusion.
“(Depending on) the diet makeup, you can have a very wide variety of colour ranges,” says Louis-Philippe Dessureault, an animal science technician at McGill University’s Macdonald Campus Farm, where they provide eggs to dining services as part of the McGill Feeding McGill initiative. A diet rich in grains, such as barley, oats and wheat, yields paler egg yolks. At the other end of the spectrum, foraging birds feeding on acorns could lay brown-yolked eggs.
The chlorophyll in kale and other plants can make yolks green, says Elijah Kiarie, a poultry nutritionist and professor at the University of Guelph’s Department of Animal Biosciences. Bédécarrats adds that farmers can give their yolks a reddish tint by using red bell pepper as a feed ingredient.
Is a darker egg yolk more nutritious?
A darker yolk doesn’t necessarily mean more nutrition. “There’s absolutely no nutritional benefit of having a pale, yellow, orange or even green yolk. We can even have a green yolk, for example, or a brown yolk. There’s no difference in the nutrients,” says Kiarie.
Free-range eggs often have more intensely coloured yolks because the hens forage for different foods outdoors, including plants and insects. They can also have more omega-3 fatty acids in their yolks due to diversity in their diets. “People think it’s healthier. Well, it’s not necessarily because the yolk is darker that it’s healthier,” says Bédécarrats.
Hens are egg-producing “powerhouses,” says Dessureault. Eggs contain everything a viable chick needs to develop. “In terms of nutrition, there’s very little variation.” Rathgeber agrees, saying colour isn’t an indicator of nutrient profile. “Chickens, in general, are all trying to deliver the same nutrients for the developing chick.”
Enriching eggs with supplements, such as lutein (a carotenoid related to vitamin A, important for eye health) from marigold flowers can result in darker yolks. Associating enrichment with a sunnier colour may explain why people think darker egg yolks are healthier. “Anything that’s going to be supplemented with lutein is going to be quite a dark yellow egg,” says Rathgeber. “But just because the egg is darker and yellower doesn’t necessarily mean it’s more nutritious than a pale-yolked egg.”
Though people may assume that a bright, bold egg yolk means more nutrition, poultry nutritionists can formulate diets for cage-laying hens that provide the same nutrients as pasture-raised chickens, says Doug Korver, professor emeritus of poultry nutrition at the University of Alberta’s Department of Agricultural, Food and Nutritional Science. “We can tailor the nutrient composition. So, it’s not a question of nutritional value. It’s more a question of consumers’ expectations and how the industry meets them.”
Likewise, some assert that darker-yolked eggs equal better flavour. Pigments represent a tiny fraction of egg yolks, explains Korver. They have a big effect on colour but not flavour. “Most of the pigments are carotenoid pigments, so they’re related to vitamin A. Some of them have vitamin A activity. Others don’t. But really, the pigments themselves have a very minor impact on the nutritional quality, the texture, the flavour of the egg. It’s more a visual thing.”
What colour egg yolk do consumers expect?
Originally from France, Bédécarrats explains that in Europe, people prefer yellow yolks, while in Japan, they tend to like darker orange yolks. “I’ve travelled to other places around the world, and there’s definitely a perception from the consumer perspective that there’s a certain colour which corresponds to a good, healthy egg — and every deviation may be a sign of something wrong.”
Even within Canada, people have different expectations based on the yolk colour they’re accustomed to.
“As soon as you hit the Manitoba border, the egg yolk colour gets very pale in comparison because they are feeding a lot less corn — if any corn. Anything in Ontario east is largely a corn- and soybean-based diet, and Manitoba west, it’s mostly wheat and canola meal,” says Rathgeber, adding that the colour difference comes down to the pigments in corn versus wheat, not soybean versus canola. “If you eat Prairie eggs, you’re going to notice that they’re not near as dark as anything from Eastern Canada.”
In many markets, yolk colour is “really important,” says Korver. For example, in Alberta, when the price of corn drops relative to the cost of wheat, poultry nutritionists will limit the corn in the hens’ diet because Albertans expect a paler yolk. Similarly, when wheat prices drop relative to corn in Ontario and Quebec, they’ll ensure they’re not adding so much that the pigmentation drops. “It’s really about addressing consumer expectations.”
How do you measure yolk colour?
Bédécarrats says that the standard way to measure egg yolk colour is still a 16-scale fan resembling paint swatches, going from light to dark.
Rathgeber’s lab uses colorimeters — specialized spectrophotometers for measuring colour. For scientific studies, they break the egg yolks into crystal cups and measure the three coordinates that make up the colour description. “We’re such visual people that for our food, people definitely decide whether they like something or not by what it looks like before they even put it in their mouth.”
Korver says we rarely see extreme orange and yellow yolks in Canada. However, consumers may expect more intensity in markets such as Australia and parts of Europe. Producers could then add natural and synthetic pigments to hit the target range. “Those extremely pigmented eggs are usually not just from typical feed ingredients. So, in some markets where that really intense pigmentation is important, products can be fed like marigold petals. Nutritionists will add marigold petals to the feed, and then those pigments from the marigold petals are incorporated into the yolk.”
Do happy hens lay golden yolks?
Whether free-range, free-run or caged hens, the colour of the yolk depends on their diet.
Backyard hens eating food scraps like carrot peels or pecking at pumpkins will have more carotenoids in their feed, says Dessureault. “That will translate almost directly to a shift in colour for the yolks, which will be a bit redder, darker, and maybe more pleasing to the eye.”
As Korver underscores, there are ways to achieve that same yolk colour using natural or synthetic pigments. “So, simply having an intensely pigmented yolk doesn’t prove that a bird had access to the outside or access to fresh plant material.”
Some people associate a deeper yolk colour with better animal welfare, but a yolk’s colour isn’t a definitive indicator of a hen’s health, says Bédécarrats. “If you’ve got a very unhealthy hen, you’ll start to observe some defects, which may translate to the yolk colour. But that doesn’t mean that if it’s a pale egg, that’s necessarily an unhappy or unhealthy hen. Not at all. Being unhealthy can impact the egg, but the egg in itself is not an indicator of the animal’s health status.”
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