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Take for example a custard. I recall reading somewhere, probably on the internet, that heating it to 70C will kill all the bacteria in it for sure. I also recall reading that holding it for 5 minutes at 60C will do the same thing.

I’m having trouble finding a proper reference for this. Is what I said actually true? It must have been studied in food science, so is there a proper source for this?

  • there are also this and this questions about egg pasteurization... – Luciano Oct 3 '18 at 9:27
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According to J.D. Schuman, info that I found in Douglas Baldwin's guide for sous-vide:

Place egg in a 135°F (57°C) water bath for at least 1 hour and 15 minutes (Schuman et al., 1997).

J. D. Schuman, B. W. Sheldon, J. M. Vandepopuliere, and H. R. Ball, Jr. Immersion heat treatments for inactivation of Salmonella enteritidis with intact eggs. Journal of Applied Microbiology, 83:438–444, 1997.

This is for whole eggs in the shell, so for your custard the time should vary according to the volume (as it will take longer for the temperature to reach the center).

Here is a time table for Salmonella reduction from The Modernist Cuisine (by Nathan Myrvold):

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  • I would expect the time to be quite different at the same temperature. In a 57C water bath the middle of the egg will take a significant fraction of that time to get anywhere near warm enough to pasteurise, but in custard you have convection and stirring to distribute the heat. The difficulty is knowing how much less time. In the other hand if that's cool enough that nothing cooks, you might not care – Chris H Oct 3 '18 at 11:53
  • I agree with Chris -- the issue is how deep the heat has to penetrate. You have to get the middle up to 60°F, and then wait a certain amount of time, and thicker items will take longer to get up to temp. Take a look at the beef section of the Baldwin guide. It's also possible that it takes longer to heat up some things vs. others (although some of that variation is from different bugs that you're trying to kill) – Joe Oct 3 '18 at 13:39
  • @ChrisH true, I fixed the information about the egg time. I assume in the table I included the times are for holding ingredients at that temperature, not total cooking time. – Luciano Oct 3 '18 at 14:02
  • According to Juneja et al., 2001, which Baldwin cites for his D-values, the numbers are different for Salmonella in broth and in meat, which I think is interesting. It's possible that the numbers for liquid eggs, whole eggs, and roasted meat might be noticeably different. IIUC, their numbers for chicken broth give a time of ~18s at 65C (D=3min at 58C, z=6.5C), but the Modernist Cuisine table gives 1m28s instead. – Kirill Oct 5 '18 at 8:37

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