Leena Watts
The colour of egg yolks is influenced by a variety of factors, including the diet of the hen, seasonal changes, and the use of additives or colourants in commercial feed. Hens that consume yellow-orange plant pigments, such as carotenoids from marigold extract, tend to lay eggs with darker and more vibrant yolks. On the other hand, a diet of corn or wheat can result in paler yolks. While the yolk colour does not necessarily indicate nutritional value, it can be a reflection of the hen's overall health and the natural diversity of their diet.
| Characteristics | Values |
|---|---|
| Dietary additives | Carotenoids, marigold extract, maize, wheat, corn, turmeric, tomato powder, alfalfa, grass, herbs, chilli |
| Yolk colour | Pale yellow, deep yellow, orange, reddish, light, dark |
| Hen diet | Seasonal vegetation, critters, insects, grains, bugs, grass, weeds |
| Hen health | Healthier hens produce deeper golden-coloured yolks |
| Hen living conditions | Free-range hens have more varied diets |
| Hen feed | Developed by poultry nutritionists |
| Hen behaviour | Hens eat more in winter to stay warm |
| Hen egg-laying | Hens with access to grass pasture produce darker yolks |
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What You'll Learn
The effect of carotenoids on yolk colour
The colour of egg yolks can vary from light yellow to deep orange. The colour of the yolk is influenced by the diet of the hen that laid the egg. For example, the diet of pasture-raised hens varies seasonally, leading to changes in the colour of the yolks they produce.
Hens are unable to synthesise xanthophylls, so the colour of the yolk depends on the quantity, colouring capacity, and stability of the dietary carotenoids they consume. Carotenoids are pigments that can be found in various natural and manufactured sources. The pigmenting efficiency of carotenoids depends on their digestibility, transfer, metabolism, and deposition in target tissue, as well as their colour hue.
Several studies have investigated the effect of carotenoids on egg yolk colour. In one study, Rhode Island Red and Silky Fowl hens were fed a basal diet with different additives: paprika extract, marigold petal extract, or Paracoccus cell powder. The colour and carotenoid content of the yolks differed significantly between breeds and diets, with the Silky Fowl hens producing yolks with higher total carotenoid content.
Another study examined the effect of dried basil herb, calendula flowers, and dandelion flowers on egg yolk colour compared to a commercial pigment and marigold flowers. The yolks from all diets differed in carotenoid profile, with the 3% supplementation level resulting in a similar total carotenoid content as the control group, but lower than the 3% marigold group. The plant parts also had high antioxidant activity, suggesting that they could protect fatty acids in egg yolks and improve egg quality.
The poultry industry uses tools such as the DSM YolkFan™ and the Roche Yolk Colour (RYC) fan to measure and standardise egg yolk colour. The colour of the yolk is not necessarily an indication of its nutritional value, but rather a reflection of the hen's diet and overall well-being.
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The impact of hen diet on yolk colour
Diet is a major factor in determining the colour of a yolk. The colour of the yolk is more closely linked to the feed of the hen than to the overall nutritional value of the egg. The carotenoids in a hen's diet will influence the colour of the yolk. For example, a diet of corn or wheat will result in a pale-coloured yolk, whereas a diet of plants with yellow-orange pigments will result in a more orange-coloured yolk.
The poultry industry uses tools such as the DSM YolkFan™ and the Roche Yolk Colour (RYC) fan to measure and standardise egg yolk colour. The RYC fan, for example, ranges from 1 (pale yellow) to 15 (dark orange). The EU regulation for organic egg production requires 4 m2 of outdoor area per hen, and increasing the area of attractive grass-herb cover has been shown to impact egg yolk colour.
The diet of a hen can vary depending on the season, and this can affect the colour of the yolk. For example, hens may eat less in the summer due to warmer temperatures and more in the winter to stay warm, resulting in variations in yolk colour throughout the year. The type of feed can also vary depending on the season, with hens being fed alfalfa silage in the spring and maize silage in the winter, which can impact yolk colour.
The addition of certain foods to a hen's diet can also influence yolk colour. For example, carrots, tomatoes, marigolds, and annatto seeds in the diet can result in deeper-coloured yolks, while flax seed can lighten the colour of the yolk. Herbs such as basil and chicory leaves have also been shown to impact yolk colour when fed to laying hens.
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How additives affect yolk colour
The colour of an egg yolk is influenced by a variety of factors, including the hen's diet, overall health, and living conditions. While the nutritional value of an egg is determined by factors like protein content, amino acid profile, and vitamin and mineral content, the colour of the yolk is more closely linked to the feed of the hen.
Additives in the form of carotenoids are commonly used to enhance the colour of egg yolks. Carotenoids are fat-soluble substances found in plants like corn and red peppers, or they can be synthetic, such as canthaxanthin or beta apo-8-carotene ethyl ester. These additives are used to create deeper shades of orange or yellow in the yolk, which is often perceived as an indicator of quality by consumers.
The type of carotenoid used can vary, with nine carotenoids approved as feed additives in the European Union. These include five natural products and four artificial products, with six having a yellow colour and three having a red colour. The ratio of yellow and red carotenoid pigments is crucial in achieving the desired yolk colour.
In addition to carotenoids, other additives such as turmeric, saffron, and marigold extract have been shown to intensify egg yolk colour. These additives can be used to create more orange or golden-toned yolks, which are particularly preferred in Southern Europe.
It is important to note that while additives can influence yolk colour, they may not always reflect the nutritional value or the living conditions of the hens. The housing system, nutritional management, and the overall health of the hen can also impact yolk pigmentation.
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The role of hen health and lifestyle on yolk colour
The health and lifestyle of a hen play a significant role in the colour of the egg yolks it produces. The diet of the hen is the primary factor influencing yolk colour, with the presence of certain pigments and carotenoids in the feed determining the depth and hue of the yolk. For example, a diet rich in yellow-orange plant pigments, such as carotenoids from marigolds, corn, or grass, will result in darker, more orange yolks. Conversely, a diet composed primarily of wheat or other grains may lead to paler yolks.
The variety and seasonality of a hen's diet also contribute to yolk colour variation. Pasture-raised hens that roam freely and consume a diverse range of vegetation, insects, and other critters tend to lay eggs with varying yolk colours throughout the year. For instance, during warmer seasons, they may eat less and produce lighter-coloured yolks, while in winter, increased feed intake for warmth can result in darker yolks.
Additionally, the overall health and well-being of the hen can impact yolk colour. Healthy hens that are active and have access to outdoor areas and natural feed tend to lay eggs with deeper-coloured yolks. The lifestyle of the hen, including its ability to move around and forage, can also influence the yolk's appearance.
While the colour of the yolk is not a direct indicator of nutritional value, it can provide insights into the hen's diet and lifestyle. The addition of colourants or additives to hen feed by large poultry operators can also manipulate yolk colour to meet consumer expectations, further complicating the relationship between hen health and yolk colour.
In summary, the role of hen health and lifestyle on yolk colour is complex and multifaceted. While diet is the primary driver of yolk colour, the overall health, activity, and natural environment of the hen can also influence the depth and hue of the yolks it produces.
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Consumer expectations of yolk colour
Consumers have certain expectations of yolk colour, which are influenced by a variety of factors. Firstly, it is important to note that yolk colour is primarily determined by a hen's diet. Carotenoids, found in plants with yellow-orange pigments such as marigolds, corn, and grass, are the pigments responsible for the yellow to orange colour of yolks. Therefore, the colour of the yolk can vary depending on the hen's access to these pigmented foods.
Historically, when eggs were first incorporated into the human diet, orange yolks were expected, signifying quality. This expectation persisted post-World War II in Europe, where consumers preferred yolks with a deeper yellow colour due to the wheat-based poultry feed at the time, which resulted in paler yolks. To meet consumer demands, the poultry industry adopted tools like the DSM YolkFan™ to standardise and measure yolk colour, with the latest version reflecting the market's preference for a deeper orange shade.
Additionally, consumer expectations of yolk colour can be influenced by the time of year. For example, pasture-raised hens may produce lighter yolks in the summer due to warmer temperatures reducing their feed intake. Conversely, their yolks may become darker in the winter as they consume more food to stay warm. This seasonal variation in yolk colour can create an expectation among consumers that yolk colour should remain consistent throughout the year.
To meet consumer demands and expectations, large poultry operators often manipulate yolk colour by adding colourants and carotenoid supplements to hen feed. This practice has led to unrealistic expectations among consumers about the natural colour of yolks and has reinforced the notion that all eggs should have the same colour yolk year-round.
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Frequently asked questions
The colour of a yolk is directly linked to the diet of the hen that laid it. A varied diet with plenty of green foods, even grass, will result in deeper-coloured egg yolks.
Alfalfa, yellow maize (corn), orange peels, annatto seeds, and marigolds will all result in deeper-coloured yolks.
Wheat-based diets will produce lighter yolks than corn-based diets. Flax seed is also known to lighten the colour of egg yolks.
While darker yolks are often indicative of a nutritionally better egg and a healthier hen, this is not always the case. The nutritional value of an egg is determined by factors like its protein content, amino acid profile, and vitamin and mineral content.
