How to tell if eggs have gone bad?

In this brief guide, we will answer the query, “How to tell if eggs have gone bad?” and will discuss different ways to detect bad eggs.

How to tell if eggs have gone bad?

To tell if eggs have gone bad, simply set your eggs in a dish filled with cold tap water. They are fresh and edible if they descend to the bottom and lie flat on one side. Because of the enormous air cell that develops at its base, a poor egg will float. Floating eggs should be discarded.

In an egg, water evaporates and albumen becomes thinner during storage, so specific gravity of an egg decreases gradually, which can be measured to get freshness. It is determined by salt water floatation method: 68 g NaCl is added into 1000 ml water, which is determined as level 0. Adding 1 grade, another 4 g NaCl is added, totaling 9 grades. Starting from Grade 0, an egg is put into the brine step by step, and the least brine specific gravity of a drifted egg is freshness level; a fresh egg is classified as above Grade 3 (1).

 Easy Ways to Determine Whether an Egg Is Good or Bad

Almost everyone has been in this situation: you grab an egg in the fridge but can’t recall how long they’ve been there.

The quality of an egg indeed degrades with time as the air pocket inside becomes bigger and the whites get thinner. There is a decrease in thickness of egg albumen and egg yolk. One of the most significant changes is an increase in air cell area due to loss of water and CO2 through the shell, along with the decay of albumin and yolk (1).

An egg, on the other hand, only “goes bad” when it begins to deteriorate due to bacteria or mold. In many countries, eggs must be washed prior to commercialization due to sanitary regulations. Washing and sanitizing the eggs under optimal conditions can reduce the microbial load to a range from hundreds to thousands (102 to 103) cfu / egg. However, washing may remove at least a portion of the cuticle, which is a waxy deposit on the shell surface which seals the pores against microbial penetration and minimizes moisture loss. Without the cuticle, the egg may rapidly be susceptible to spoilage. Therefore, storage under refrigeration is recommended (2).

Your eggs could be OK to consume for a few more weeks. If you’re unsure if your eggs are okay or rotten, there are a few strategies you may utilize. The top four are listed below.

In the food industry, several non-destructive tests have been developed to identify the properties of the inside and outside of an egg. Raw egg freshness indexes include sensory indicators, air cell height, Haugh unit, pH value, yolk index, the specific gravity of eggs, and total volatile basic nitrogen content. Even without special equipment, it is possible to determine whether an egg is safe to eat (1).

 Make sure to check the expiration date

Checking the date on the carton is one of the simplest methods to know whether your eggs are still okay. However, if you discard your refrigerated eggs as soon as the expiration date approaches, you may be squandering perfectly excellent eggs.

Depending on which state you reside in, eggs in the United States may be tagged with a “sell by” or “expiration” date to indicate if they are still fresh. A “sell by” date specifies how long a retailer should keep eggs on the shelf — no more than 30 days after packaging — but it does not mean the eggs are bad.

An expiry date, on the other hand, indicates when the eggs are no longer regarded as fresh. If none of these marks are present, another date might be used to determine how fresh your eggs are.

The “pack date,” which is the day the eggs were graded, cleaned, and packed, is required to be shown on the carton of eggs that have been graded by the USDA. However, if you don’t know what to look for, you can miss it.

The “pack date” is printed as a Julian date, which means that each day of the year is assigned a numerical value. As a result, the numbers 001 and 365 are used to represent January 1st and December 31st, respectively.

You may be relatively confident your eggs are still fresh if they are still within the expiry or “sell by” date on the carton, or 21–30 days after the “pack date.” Even though an egg’s quality begins to deteriorate after a specific date, it may be safe to consume for many weeks if it has been refrigerated, which retains quality and inhibits bacterial development.

If your eggs are over the expiration date on the box, you’ll have to rely on another way to determine if they’re good or rotten.

 Perform a Sniff Test

The nose test is the oldest, simplest, and most accurate technique of determining whether or not an egg is spoiled. Whether your eggs have passed their “sell by” or expiry date, a simple scent can tell you if they are still edible.

The egg shell is porous, and this allows the odors to exhale, which are mostly present in the yolk and fat soluble. Off-flavors caused by spoilage are volatile gasses such as ammonia oxides, alkanes, and alcohols. Off-flavors can also be caused by rations with poor quality fishmeal containing rancid oil, or by birds having access to garlic, certain weed seeds, or other materials foreign to normal poultry rations (2).

Whether raw or cooked, eggs that have gone rotten will have an identifiable odor. If you can’t tell while the egg is still in its shell, break it onto a clean dish or bowl and smell it. If the egg smells bad, throw it and wash the dish or plate in hot, soapy water before using it again. It’s a positive indicator that the egg is still safe to use if it smells normal, or if there is no odor at all.

 Conduct a visual examination

Your eyes, in addition to your nose, are an important tool for determining if an egg is excellent or poor. Check sure the egg’s shell isn’t broken, slimy, or powdery while it’s still in its shell. Bacteria may be detected by sliminess or fissures, whereas mold can be detected by a powdery look on the shell.

Before usage, break the egg onto a clean, white dish or plate if the shell seems dry and unbroken. Check the yolk and whites for any pink, blue, green, or black discoloration, since this might indicate bacterial development. Fresh eggs have clear and firm whites, and an outline of fairly well defined yolk, that is practically free from defects, free form odors. Spoiled eggs have weak and watery whites or may have small blood and meat spots present, the yolk has outline plainly visible enlarged and flattened, may have clearly visible germ development and have other serious defects (2).

If the egg seems to be discolored, discard it and wash the dish with hot, soapy water before trying a fresh egg.

You may also test whether the egg whites or yolk are still runny. This indicates that the egg is old and its quality has deteriorated. However, this does not always imply that it has gone bad; it may still be entirely safe to use.

Candle your egg

Candling is a technique for determining the quality of a table egg or the growth of a fertilized egg’s offspring. This is done at a factory using specialized equipment to guarantee that table eggs are properly graded before being packed.

The technique of egg candling has been used for centuries. In the mid 19th century, for example, upper-scale restaurants used to check incoming eggs for freshness by viewing their internal contents by candlelight. The chef looked for air cell size, distinct yolk shadow, and dark bodies (blood spots). Blood and meat spots, enlarged air cells, weak albumens and prominent yolks are the more common internal defects  (2).

If you’re willing to learn, you can do it on your own eggs at home. A dark chamber and a modest, bright source of light are required. Candles were utilized in the past, thus the term “candling.” However, a modest flashlight or reading light is likely to be more effective. Inside the dark candling booth a strong source of light under the conveyor exposes the egg’s internal defects, as well as shell defects to the operators (candlers) (2).

Bring the light source up to the egg’s big end. After that, tilt the egg and swiftly turn it from left to right. The contents of the egg should be lighted if done properly.

This enables you to determine if the air cell in the egg is tiny or big. The air cell in a very fresh egg should be narrower than 1/8 inch (3.175 mm). Gasses replace water lost via evaporation as the egg matures, and the air pocket becomes bigger. When the air cell is still 3/16 inch or less in depth and has unlimited movement and is free or bubbly, the egg is safe to eat. Altered characteristics may indicate that the egg is no longer fresh and safe (2).

You should be able to detect how hard the egg white and yolk are by moving the egg from side to side. A fresher egg will have less movement. Candling may take some experience, but it is a reliable way to tell if an egg is fresh or old. However, it, like the float test, is unable to determine if an egg has gone rotten.

Other FAQs about Eggs that you may be interested in.

How long do hard-boiled eggs stay good?

How long do boiled eggs stay fresh?

How long do I cook hard-boiled eggs?

Conclusion

In this brief guide, we answered the query, “How to tell if eggs have gone bad?” and discussed different ways to detect bad eggs.

References

1. Qi, L., Zhao, Mc., Li, Z. et al. Non-destructive testing technology for raw eggs freshness: a review. SN Appl. Sci., 2020, 2, 1113. 
2. Zeidler, G. 2002. Shell Egg Quality and Preservation. In: Bell, D.D., Weaver, W.D. (eds) Commercial Chicken Meat and Egg Production. Springer, Boston, MA.