Why are some egg yolks so orange?
March 23, 2020 Annabel Slater By Annabel Slater My Articles

Why are some egg yolks so orange?

Does egg yolk colour matter? And why are yolks from different countries different colours?

When I was growing up, we used to keep free-range chickens. We’d buy them from battery farms - gawky young birds with missing feathers and blinking greyish-yellow eyes that had never seen sunlight. When let outside for the first time, they’d voraciously peck at anything green and living. 

As they settled into their new life, everything about them changed. Their combs turned from anaemic pink to rich vibrant red, stubbly feathers blossomed into patterned plumage, and the yolks of their eggs turned from pale whitish yellow to a deep amber colour.

What could be clearer? Regular sunlight and country living produced happy, healthy hens and eggs that were bursting with colour.

Well…I was both wrong and right.

Why are egg yolks yellow or orange?

Egg yolks get their colour from carotenoids. Carotenoids are plant pigments, responsible for red, orange and yellow hues in certain vegetables and fruits. You might guess then that carrots, pumpkins, peppers, Vietnamese gac fruit, and sweet potatoes are all particularly rich in carotenoids.

But carotenoids are also found in green plant material, because carotenoids absorb light for photosynthesis and protect the plant from sun damage. The reason some trees turn brilliant shades of yellow and orange in autumn is because you can see the colour of the carotenoids as the green chlorophyll disappears.1 

Chicken’s diet changes the egg yolk colour

So, our free-range chickens gained carotenoids from the grain, grass and plants they ate. Their yolks changed colour because carotenoids accumulate in fat, and about a third of the yolk is fat.

This means carotenoids can also colour animal fat tissue - including your own. If you ate an excessively high amount of squash, you would develop carotenemia - orange-tinted skin!2 If that’s hard to imagine, just look at flamingos. Their pink-orange feathers are made from fats rich in carotenoids from the shrimp and algae they eat.3

Are yellow egg yolks better than orange egg yolks?

Since chickens around the world traditionally received different diets, there are cultural preferences for different yolk colours. Surveys show people in northern European countries prefer lighter yellow yolks, while people from southern countries –though also including Germany–want dark, deep orange yolks.5 And people in South Africa are used to egg yolks which are nearly white, due to the chickens’ diet of sorghum and local white maize, which are low in carotenoids.5

Consumers think yolk colour is the most important quality for eggs and represents the healthiness of the egg and the chicken itself. The reality is that the colour could be artificially enhanced.

The science behind egg yolk colours

There are two classes of carotenoids:

  1. Carotenes, which tend to produce reddish colours, and
  2. Xanthophylls, which produce yellow shades.

Farmers can adjust yolk colour through the chickens’ diet. Small scale farmers can directly feed plant material naturally high in carotenoids (e.g. algae, alfalfa, citrus peel, fortified corn), while larger-scale farmers rely on processed feed that contains such ground-up plant material or synthetic supplements.

Processed poultry feed is a blend of grain, protein, vitamins and minerals. In Europe, the EU Register of Feed Additives lists which xanthophylls and carotenes can be added. So, a large-scale farmer has to strike the right balance of yellow and red carotenoids to keep the shade consistent. The types and ratios of carotenoids in feed and eggs will depend on what yolk colour consumers want, and farmers provide.

There are regulations monitoring how much of each xanthophyll can be safely added to feed. The EU allows 80 mg of canthaxanthin per kg of animal feed.7

What carotenoids are in chicken feed?

The most commonly added xanthophylls in poultry feed are lutein, zeaxanthin, and canthaxanthin. While these could be found in natural sources, synthetic carotenoids are more stable and last longer in stored feed. Still, lutein is too expensive to produce synthetically, and is usually extracted from marigold flowers.4

The preferred carotenoid for reddish orange shades is canthaxanthin, so a typical egg laid in Finland might include just 0.09 mg of canthaxanthin to reach the preferred yellow shade. While an egg laid in Germany, where dark orange yolks are popular, could have up to 0.35 mg of canthaxanthin.

Fun Fact: With over 1100 known carotenoids of varying effects, there is a vast potential palette of egg yolk hues, and colour grading of yolks is taken very seriously. There’s an industry-standard book of colour swatches to assess yolk colour - the ‘DSM colour fan’. It was established in 1987 with 15 shades – a 16th shade was last added in 2016 – for human assessors.8 And for even more accuracy, there are various colour-measuring machines.

Organic egg yolk pigments

But what if the hens are producing organic eggs? They can only receive natural sources of carotenoids. So rather than receiving feed with synthetic canthaxanthin, an organic egg-laying hen might be fed tomato powder instead, which would provide the red pigment lycopene, or paprika, which contains the red xanthophyll capsanthin. But, these carotenoids don’t colour egg yolk as strongly as canthaxanthin does.6  

Egg yolks & your health

Without scientific testing, you cannot know what carotenoids are in your egg, or how much. Lutein may protect against macular degeneration – a permanent loss of sight caused by declining retinal cells. A study found ‘normal’ Dutch eggs contained 167.8 micrograms of lutein per yolk, while chickens fed a diet enriched with lutein produced yolks contained 921.4 micrograms.9

That may sound impressive, but there could be better sources of carotenoids. Another study found kale could contain almost 13 times more lutein than egg yolk, per gram.10  

Does the yolk color really matter?

A sunset-orange egg yolk might suggest its chicken was able to dine outside on plants. But perhaps the chicken just ate feed enriched with chili powder.

In the end, your egg depends on what the chicken eats, and the chicken depends on what the farmer feeds it. So, don’t worry too much about the colour – just enjoy your egg!

What colour do you like your egg yolks, and why? Let us know in the comments below!

March 23, 2020 Annabel Slater By Annabel Slater My Articles
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