Fish Taste and Smell (Taint) in Eggs

By Katie Thear

He smells like a fish; a very ancient and fish-like smell.
The Tempest
. William Shakespeare)

Several people have contacted me to say that some of their eggs are tainted, tasting and smelling fishy. One lady says that some of the table poultry she has raised also tastes of fish. What causes it and how can it be avoided?

This is one of those questions for which there is no single or simple answer so it is worth looking at all the contributory factors. Nobody really knows why some eggs and poultry should be affected while others are clear, but various avenues of research have been suggested. Incidentally, I remember once reading (but unfortunately can’t remember where) that US servicemen stationed in this country once complained that British chicken and eggs tasted fishy.

Taints in storage:

Eggs have porous shells so are capable of absorbing smells and other taints. They should therefore be stored in an area well away from foods such as fish, etc. The same is true for table chickens.

Plants on range:

Some plants such as garlic, oilseed rape and wild onion can impart taints to the eggs of free-ranging hens.

Fishmeal:

Too much fishmeal in the proprietary feed has been known to cause a problem.

Fish oil:

In recent times fish oil has been added to poultry feeds in order to increase the Omega-3 qualities of eggs. The first experiments produced fishy eggs because the oils have double chemical bonds that make them react easily and become rancid fairly quickly. An antioxidant such as Vitamin E can be used to counteract this, but getting the balance right is not always easy.

Flax seeds:

The seeds of flax as well as canola and soya beans are also sources of Omega-3. Too much flaxseed, however, can darken the yolks and leave a fishy taste within them.

Too much protein in feeds:

There is sometimes a tendency to tailor feeds, not only for maximum production but also for large eggs. Excess amino acids, choline and lecithin are thought to increase the likelihood of taints. Some free-range and organic producers prefer to grow their own cereals and have feeds formulated to their specific requirements because of this.

Wheat and wheat pasture:

Research in the USA in the 1970s, indicated that cows grazing on wheat pasture had a greater tendency to produce milk that tasted fishy. (1)

This does not mean that poultry are affected in the same way, but it is an intriguing factor. Milk or milk products are sometimes used in poultry feeds.

Fishy gene:

Some humans have a defective gene FM03 that causes a condition called Fish Odour Syndrome or Trimethylaminuria. A similar condition also occurs in cattle where the gene concerned is R238X. It is the production of the chemical trimethylamine (TMA) that produces the smell in both cases. It is now thought that a similarly defective gene may also be present in chickens. It has also been suggested that brown egg layers are more likely to be affected than white egg layers. (2) It should be emphasised however, that this is still being researched and no firm findings are yet available.

References

  1. The Undesirable Flavour of Milk Resulting from Grazing Cows on Wheat Pasture. Johnson, Odell and Smith. Oklahoma Agricultural Research Station. 1973.
  2. Ongoing Research. University of Agricultural Sciences, Upsala, Sweden.

Copyright © Katie Thear 2006

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