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So, Spud asked for a piece on eggs – and since we’ve not got any episodes coming up featuring ovoids (unless you count the Gordon Ramsey souffle episode coming in a few weeks), I thought I’d share some info on boiled eggs.

First up, a question that I’ve looked into a couple of times – are soft-boiled eggs really likely to give you salmonella?

How many eggs are infected?

Quite what the likely salmonella incidence in eggs is is a complicated question. An FSA study in 2007 showed a .38% incidence of salmonella – however, that was in cooked eggs served in restaurants and other catering places. (The same study warns that it’s best to be careful with egg product from Chinese takeaways and restaurants, which showed a very high tendancy to store eggs at ambient temperatures and pool eggs). It’s very hard to find out what the incidence of salmonella in UK eggs is – there aren’t any figures on the FSA site.

However, Andrew Wadge, Chief Scientist of the FSA, at one point refers to the UK’s having 10 times less salmonella in eggs than they found in foreign egg samples, implying an infection rate of about 1 in 300 boxes. However, the foreign egg survey also showed that 157 of the cases they found were salmonella on the outside of the egg only, with only 10 being salmonella inside the egg – and no details on how deep inside.

Given that salmonella on the shell will be killed immediately in a boiled egg, you’re talking about a 0.02% chance per box of eggs that there’s salmonella, rather than Intel, inside one of them (assuming you’re using a UK egg).

In the US, the Department of Agriculture did a survey in 2002 that showed there was an incidence of salmonella in 1 in 30,000 eggs produced in the US. That’s, erm, not very many (and almost exactly the same as my estimated UK incidence).

Harold McGee says that there’s basically no difference in infection rates between battery farmed eggs and free-range.

What precautions can you take?

The FSA and various other places advise that soft-boiled eggs aren’t safe – but the risk factor appears to be pretty darn low. Added to all the information above, whether or not the salmonella survives cooking depends on where it lies in the egg – because there’s a steep temperature gradient in boiled eggs, with the surface, obviously, getting pretty near boiling, the salmonella needs to be pretty deep into the egg to not boil alive, even if you’re cooking a soft-boiled egg.

On a practical note, I’ve been eating soft-boiled eggs for quite a few years now, with, touch wood, no salmonella so far.

Of course, you should still store eggs in a refrigerator – there’s no downside to doing that, and it prevents the growth of any salmonella that might be there. And as Heston Blumenthal and various other people point out, you should always wash your hands after handling raw eggs in their shells, because there’s actually far more likely to be salmonella on the shell than inside.

If you really want to be 100% sure, and you’re either fairly patient or have a sous-vide setup, you can pasturise eggs. Just stick them in a water bath at 57 degrees centigrade for 75 minutes for a large egg (thanks Douglas) – you can find out more in the Practical Guide to Sous-Vide. That’ll kill everything in there without coagulating the protein – although it may alter the taste and texture a bit. McGee mentions that you can also buy pre-pasturised eggs, although I’ve not seen them in the UK.

Of course, if you’ve got a sous-vide setup, you can also just cook your boiled eggs using it. Bruno Goussault, who more or less invented sous-vide, says that the perfect temperature to cook eggs is 64.5 degrees Centigrade. I must admit, I’ve tried cooking eggs sous-vide a couple of times, and the results have been a bit disappointing – but that’s a topic for another post. One thing that’s certain is that an egg held at 64.5 degrees for a few minutes will definitely be bacteria free.

So…

No, it’s not very likely that you’ll get salmonella from a soft-boiled egg, although it’s not impossible. It’s a non-zero chance, so if you’re feeding eggs to young children, adults with weakened immune systems, or anyone else who might die of salmonella infection, it might be best to be cautious.

But for a healthy adult, given the infection rates I’ve mentioned above, you’d have to eat a soft-boiled egg every day for a little under 100 years to even have an odds-on chance of encountering one contaminated with salmonella. And even then, there’s a good chance that the bacteria would die in the cooking process, or you’d just fight off the infection.

Hurrah. Back to the egg-n-soldiers for me.