Vol. XVII · Eggs and Dairy Plate 6 of 10egg safety, Salmonella Enteritidis, runny yolk, pasteurised eggs, raw egg, mayonnaise, tiramisu, vulnerable groups, refrigerationS

Eggs and Salmonella.

A six-minute egg's yolk barely reaches 55 °C. That is delicious and, for a pregnant woman or a small child, not enough.

Salmonella Enteritidis can infect a hen's ovaries and get inside the egg before the shell forms, so even clean, uncracked eggs occasionally carry it — estimates in the United States have been around one egg in 20 000, and much lower in countries with vaccination programmes such as the UK's Lion scheme. Refrigeration keeps any bacteria from multiplying (XII.3); cooking kills them, but only if the inside gets hot enough for long enough (XII.5).

A runny or jammy yolk does not. A boiled egg's yolk centre that never passes 60 °C receives only a small log reduction. For healthy adults the remaining risk is very small; for infants, the elderly, pregnant women and the immunocompromised, health agencies advise eggs cooked until yolk and white are firm, or pasteurised eggs — held in warm water long enough to kill Salmonella without setting the white — for anything raw or lightly cooked: mayonnaise (X.4), tiramisu, mousses, eggnog, soft-boiled eggs. The workshop measures the kill at the yolk's centre.

Below: the log reduction of Salmonella at the centre of the yolk for a large egg boiled for the minutes you choose (thermal bench, course D and z for Salmonella), against the 5 logs that pasteurisation aims for, and the time pasteurisation takes at 57 °C and 60 °C.

What you will learn
Workshop
Thermal bench: a large egg (45 mm sphere) from 5 °C, boiled for the minutes chosen, then 3 minutes in iced water; log reduction accumulated at the yolk's centre with the course Salmonella parameters (D(60 °C) 1.73 min, z 5.6 °C; eggs may differ). Pasteurisation: 5 logs at the temperature, the target commonly used for liquid and in-shell egg pasteurisation.

Firm for the vulnerable, pasteurised for raw

In this model a six-minute egg's yolk centre peaks near 54 °C and achieves a log reduction of only about 0.03 there; a nine-minute egg, its yolk set nearly through, achieves about 54 — far past the 5 that counts as safe. Pasteurising at 57 °C takes about 30 minutes for 5 logs, at 60 °C about 9 — which is why in-shell pasteurisation holds eggs in carefully controlled warm water for an hour or more, just below the point where the white begins to cloud.

Practical rules. Buy eggs from a refrigerated case, keep them cold, and do not use cracked or dirty ones. Wash hands after handling raw eggs (XII.8). For dishes with raw or lightly cooked egg served to the vulnerable, use pasteurised eggs or pasteurised liquid egg. Cook eggs for them until the yolk is firm, and egg dishes (quiches, custards, casseroles) to 71 °C (XII.6). For everyone else, a runny yolk from a fresh, refrigerated egg is a very small risk, and in countries with vaccinated flocks smaller still.

At the stove

Read the label of your eggs: is there a vaccination scheme mark or a pasteurisation statement? Find where pasteurised eggs or liquid egg are sold near you for raw-egg recipes.

Salmonella Enteritidis in eggs became a public-health issue in the 1980s; the UK's Lion mark scheme, introduced in 1998 with vaccination of laying hens, cut cases so far that in 2017 the Food Standards Agency advised that Lion eggs could be eaten runny even by vulnerable groups.

Terms

Salmonella Enteritidis
The Salmonella type that can infect eggs from inside.
Pasteurised eggs
Eggs heated gently to kill Salmonella without cooking them.
Vulnerable groups
Infants, the elderly, pregnant women and the immunocompromised.
Lion mark
The UK scheme for eggs from vaccinated hens.
A runny yolk gets too little heat for a real kill. For the vulnerable, cook eggs firm or use pasteurised eggs; keep all eggs cold.

Sources

  1. USDA FSIS, Appendix A to the Compliance Guidelines for Meeting Lethality Performance Standards for Certain Meat and Poultry Products (time–temperature table for 6.5- and 7-log reductions of Salmonella in cooked beef).
  2. USDA Food Safety and Inspection Service, "Safe Minimum Internal Temperature Chart" (foodsafety.gov), 2024.
  3. A teaching value chosen for the course: the right order of magnitude and shape, not a measurement of a particular food.