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Duck eggs seem to get about a 6-week extension on their expiry date over Chicken eggs. (the latest pack I bought yesterday expire May 25th, where as the Chicken Eggs at best were Mid-April).

Why is this? Is the structure of the Shell or does it have to do with the protein structure of the Egg Whites? I have seen the same thing with Quail Eggs as well they also get a long away expiry date.

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up vote -3 down vote accepted

Interesting question, tried to search and it is very hard to find any real answer, I did find this link which speculates that since duck eggs have thicker shells they have longer shelf life.

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First of all, eggs are generally much more robust than commonly thought. Food safety advices for eggs vary a lot, but healthy (chicken) eggs can stay good for many months. If the eggs are contaminated with bacteria when laid or during processing, they can of course spoil or rot before their "best before" date as well. I didn't find any publications, but in this interview, a researcher from Nofima (a Norwegian food research institute) tells that they were not able to find any harmful bacteria in 7 months old eggs and even after 12 months, eggs are usually edible.

Back to the difference between chicken and duck eggs ... Chicken eggs are good for at least three weeks even without refrigeration. The reason for this is that the eggs contain natural preservatives, which are required for the egg to stay good during the nesting period. The natural purpose of the egg is of course to provide nutrition to the contained chicken, and it would probably not do the chicken any good, if it has to stay with a rotten egg yolk for several weeks. It varies between different duck species, but ducks generally breed their eggs much longer than hens. I am now just assuming, but I suppose that duck eggs have a similar natural protection as well, to keep them good throughout the longer breeding period and that may explain the longer recommended shelf life for duck eggs.

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nice. +1 for nature argument. – MandoMando Mar 20 '13 at 15:58
Interesting, from internet , chicken eggs hatch in 21 days, duck eggs in 28 (Muscovy 35), quail eggs 23 days, goose 25-27, Ostrich 40-43, but remember eggs are often washed which reduces the shelf life. – Stefan Mar 21 '13 at 1:31
An issue mentioned by several others is washing. Generally in Europe eggs are not washed before being sold and in North America they are. Washing removes most of the cuticle, making the shelf life shorter. This is why eggs are generally found in the fridge in North America and not in (all countries in) Europe. This article has a lot of information - among others, that up until recently, US eggs were often stored up to a year before being sold. – Erik P. Mar 24 '13 at 19:09

I suspect it's an issue of volume. Chicken eggs are a huge commodity and a lot of time and effort goes into USDA grading, etc. Duck eggs are a smaller market and not usually graded which means they can get from the farm to the store much faster.

In many countries eggs aren't power washed and bleached like they are in the US so eggs can be sold and stored unrefrigerated for long periods without any ill effects.

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Volume issues might not necessarily be grading related -- there's a relatively fixed demand for chicken eggs, and I'm guessing there are various stockpiles somewhere to absorb short-term changes in demand. Those eggs you buy in the store might've already spent a couple of weeks in a warehouse. Duck eggs, being a niche item in many markets, is less likely to have that extra infrastructure. – Joe Nov 18 '13 at 19:10

Duck eggs have a heavier, more waxy coating on them than chicken eggs do. Duck eggs must be more resistant to bacteria in moist environments since they are much more likely to be exposed to it than a chicken egg is since, in nature, the duck spends much more time in the water. A heavier, more waxy coating means less evaporation and less chance for bacteria to enter the egg and multiply in storage.

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There shouldn't be any difference in shelf life if the duck eggs and chicken eggs are handled and stored in the same manner. However, it has been shown by investigative reporters that chicken eggs are often stored unrefrigerated by supermarkets, allowing them to stand at room temperature for hours before being put in the display case, so the apparently shorter shelf life of chicken eggs may be due to the producers erring on the side of caution when they label the cartons.

I keep my refrigerator colder than recommended, two to four degrees above freezing, and I've successfully stored chicken eggs for three months without spoilage. Even if the eggs don't spoil, however, they lose moisture, and the yolk and white may become quite thick over time. I've also encountered rotten chicken eggs that were well within the use-by date, presumably because the egg got infected even as it was developing inside the chicken.

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Thanks Andrew. Chickens are usually dated for 8-weeks. Each day out of the fridge counts as 1-week. With Duck eggs, I regularly see expiration dates way past 8-weeks from seeing them in the store, let alone the lay time. – MandoMando Mar 19 '13 at 21:13

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