Salmonella is a concerning bacteria that can contaminate eggs and cause foodborne illness. Proper cooking is essential to kill any potential salmonella in eggs and make them safe to eat. This article examines the best practices for cooking eggs thoroughly to destroy salmonella.
What is Salmonella and How Does it Get in Eggs?
Salmonella is a genus of bacteria that contains over 2,500 different serotypes. There are two species of salmonella that commonly cause disease in humans – Salmonella enterica serotype Typhimurium and Salmonella enterica serotype Enteritidis (1). Salmonella lives in the intestines of animals, including poultry like chickens and ducks. The bacteria can be passed into the eggs before the shell forms or via contamination from feces during the laying process (2).
Salmonella is quite hardy and can survive for long periods outside of an animal host. If an eggshell becomes contaminated, the bacteria can penetrate into the interior of the egg. Salmonella prefers to grow at temperatures between 35-37°C but can multiply at temperatures between 8-45°C (3). This wide temperature range means eggs must be thoroughly cooked to destroy any potential salmonella.
What are the Symptoms of Salmonella?
If eggs contaminated with salmonella are consumed raw or undercooked, the bacteria can cause salmonellosis food poisoning. Symptoms generally begin 6-72 hours after ingestion and include (4):
- Diarrhea
- Fever and chills
- Abdominal cramps
- Nausea and vomiting
- Headache
In healthy individuals, salmonellosis usually resolves on its own within 4-7 days. However, salmonella infection can be life-threatening for vulnerable groups like infants, elderly, pregnant women and those with weakened immune systems. Salmonella can also spread from the intestines into the bloodstream and cause a dangerous, systemic illness.
How Common is Salmonella Contamination in Eggs?
The prevalence of salmonella contaminated eggs is relatively low in developed countries. In the United States, an estimated 1 in every 20,000 eggs may be internally contaminated with salmonella (5). Stringent sanitation requirements during hen housing and egg processing have reduced contamination rates over the past few decades.
However, salmonella remains a potential risk with raw or undercooked eggs. The FDA Model Food Code recommends cooking eggs until the yolk and white are firm to prevent foodborne illness (6). Proper cooking is necessary to destroy any salmonella that may be present in an egg.
What Temperature Kills Salmonella in Eggs?
Heating eggs to a high enough temperature for a long enough time will kill any salmonella bacteria present. Salmonella is destroyed rapidly at temperatures above 57°C (7). The table below outlines the time/temperature combinations recognized by the FDA as sufficient to make eggs safe to eat (8):
| Minimum Internal Temperature | Minimum Time |
|---|---|
| 60°C (140°F) | 3.5 minutes |
| 61.1°C (142°F) | 3 minutes |
| 62.2°C (144°F) | 1 minute |
| 63.3°C (146°F) | 31 seconds |
| 68°C (155°F) | Instantly |
As shown, a minimum internal temperature of 68°C (155°F) instantly kills salmonella in eggs. Lower temperatures can also eliminate the bacteria if the eggs are held at that heat for the specified time. Keep in mind these temperatures must be reached throughout the entire egg.
How to Tell if Eggs Are Cooked Enough to Kill Salmonella
Checking the internal temperature of eggs requires special equipment like a food thermometer. For everyday cooking, there are some simple visual signs you can look for to ensure your eggs reach a safe temperature:
- Fried eggs: The white is completely set and the yolk is thickened.
- Poached eggs: The white is fully opaque and the yolk is thickened.
- Hard boiled eggs: The yolk and white are both completely firm throughout.
- Baked goods: No visible liquid egg remains and the center is set.
What Cooking Methods Kill Salmonella in Eggs?
Many common cooking techniques can achieve temperatures high enough to destroy salmonella in eggs. Here are some safe cooking methods (9):
Frying
Pan frying eggs in butter or oil allows the whites to fully coagulate and the yolks to thicken. Fried eggs should be cooked on both sides until no visible liquid remains.
Poaching
Poaching eggs in simmering water that’s between 82-93°C (180-200°F) causes the proteins to set into a solid white and semi-firm yolk.
Boiling
Hard boiling or soft boiling eggs heats both the yolk and white until completely firm. Boiled eggs are heated to 100°C (212°F), well above the temperature required to kill salmonella.
Baking
Baking egg dishes like quiches, casseroles or custards allow the eggs to be cooked at high oven temperatures. Bake until the center is set and no liquid egg remains.
Sous Vide
The sous vide technique involves vacuum sealing eggs and cooking them in a water bath at precise temperatures. Pastuerization occurs at 57°C (135°F) over a longer time.
Microwaving
Eggs can be scrambled, poached or baked in the microwave. Microwaves heat eggs quickly, ensuring the proteins are sufficiently cooked through.
Food Safety Tips for Cooking Eggs
Following proper food safety practices when cooking and handling eggs can minimize the risk of salmonella:
- Purchase eggs from reputable, sanitary sources like grocery stores.
- Check eggs are not cracked before purchase.
- Refrigerate eggs at 40°F or below.
- Cook eggs thoroughly until yolks and whites are firm.
- Use a food thermometer to check the internal temperature.
- Don’t keep cooked eggs at room temperature for more than 2 hours.
- Refrigerate cooked egg dishes promptly.
- Wash hands, cooking equipment and surfaces after contact with raw eggs.
- Don’t consume raw or undercooked eggs.
Who is Most at Risk from Salmonella in Eggs?
While proper cooking neutralizes the risk of salmonella in eggs for most people, some groups are more vulnerable to infection (10):
- Young children
- Elderly
- Pregnant women
- Individuals with compromised immune systems
At-risk individuals should take particular care to fully cook eggs until both the yolk and white are firm. Using pasteurized egg products can also reduce the risk of illness.
Can You Get Salmonella from Store-Bought Raw Cookie Dough?
Many store-bought cookie doughs are intended to be eaten raw. Manufacturers take steps to protect consumers from potential salmonella in the raw eggs and flour:
- Pasteurized eggs are heated to destroy bacteria.
- Heat-treated flour kills pathogens.
- Products are refrigerated.
- Facilities follow food safety protocols.
While raw cookie dough made with pasteurized ingredients poses a low risk, children and those vulnerable to foodborne illness should exercise caution (11). Homemade raw dough or baking mixes should always be fully cooked.
Can You Make Eggs Safe If You Are Not Sure They Are Cooked Enough?
If you are uncertain whether eggs reached a high enough temperature to kill salmonella, it is best to error on the side of caution. Here are some methods to help make potentially undercooked eggs safe (12):
- Return the eggs to the heat and cook until completely set.
- Bring the temperature up by microwaving on high for 2 minutes.
- For dishes containing raw or undercooked eggs, recook the entire dish to 74°C (165°F).
- If reheating is not possible, discard the food to avoid risk of illness.
When in doubt, remember the old adage: “When in doubt, throw it out.”
Conclusion
Cooking eggs thoroughly until the whites and yolks are firm eliminates the risk of foodborne illness from salmonella. An internal temperature of 68°C (155°F) instantly pasteurizes eggs. Proper handling and preparation of eggs using correct cooking times and temperatures can keep this nutrient-rich food safe to enjoy.