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I many times wonder if I can buy eggs now because not going directly to home. The temperature in cars is often very high (probably more than 40 C at direct sunlight). This answer talks about accumulation of heat to the object - maximum 4 hours at 5-60 C. However, if the temperature is very high all the time during that time, I think the maximum time is shorter.

I do not understand how bacteria can develop in eggs at high temperatures (> 40 C). In other words, how well does the package protects eggs from much heat?

How many hours can you keep raw eggs in a package in a warm car?

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    Bacteria don't start dying until at least 50C. Salmonella starts dying at 55C, and the temperature has to be sustained for some time. – ElendilTheTall Aug 12 '14 at 18:40
  • Your "in other words" is really confusing. The question of whether the package protects the eggs by keeping them cooler is completely separate from the question of whether bacteria can multiply above 40C. – Cascabel Aug 12 '14 at 21:22
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No, your reasoning is incorrect. Food safety rules are dumbed down because they have to be taken literally without any reasoning.

if the temperature is very high all the time during that time, I think the maximum time is shorter.

The maximum holding time isn't shorter for higher temperatures within the danger zone. It is the time at which food is legally safe, and it is defined to be the same for all temperatures in the 4 to 60 Celsius range, for all foods. This is different from the time the bacteria load actually increases to different levels - the real time cannot be really predicted, so the food safety rule assumes the worst case plus a safety margin.

Package isolation, actual temperature difference, actual initial bacterial load and so on are variables which you cannot measure at home, and whose effect you cannot calculate without using a model sophisticated enough to do a weather prediction (and we all know how good these are). So, they are not considered when calculating the legally safe time.

The range of 4 to 60 Celsius was chosen because it is the range at which foodborne pathogens multiply. Below 4 Celsius, Salmonela stops multiplying (but doesn't die, neither do other bacteria). Above 60, a few bacteria will survive, but practically none will multiply. The 40 Celsius limit is very low, even humans can survive it. It is a very comfortable temperature for most foodborne bacteria, whose optimal life condition is the gut of a human suffering from a fever.

If you want to base your decisions on a calculation of bacterial growth, as opposed to regulations, that's impossible. Such a calculation cannot be done even as a rough estimate. You are left with either following the regulations, or taking shots in the darkest dark.

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    Sewage treatment plants aim for about 35 to 38°C (95 to 100°F) as an ideal temperature for "digestion" (bacteria breaking things down) ... so it's a temp that you really don't want potentially dangerous food spending a long time at. (of course, you do want fermented foods at that temperature, for the same reasons ... bacteria multiply quickly) – Joe Aug 12 '14 at 21:21
  • @Joe That is a very interesting comment. Is there any other short temperature ranges which I should consider within [5,60]C? – Léo Léopold Hertz 준영 Aug 13 '14 at 6:42
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    @Masi : Yes. there's another class of bacteria used for thermophilic digestion that's most active around 49 to 57°C. (120 to 135°F). Sewage treatment plants don't tend to use this temperature range, because it requires lots of energy (and thus, costs more). – Joe Aug 13 '14 at 15:38
  • @Joe I think the temperature can reach 49-57C in a dark car during summer and sunlight. I did not find any research about some bacteria at thermophilic digestion with eggs. – Léo Léopold Hertz 준영 Aug 13 '14 at 19:30
  • I agree with most of this answer, however, bacterial growth is logorithmic. So, while the guidelines are simplified for maximum safety, the fact is, the higher the temperature (within the "danger zone"), the more quickly bacteria will grow. Ideal temp for salmonella growth is 35 - 37 C, for example. Eggs in your warm car have a shorter actual shelf life then eggs on the counter in your kitchen. Your assumption that the actual time is "much shorter" is probably correct, but I think there are too many variables to reasonably calculate exactly how much. – moscafj Jun 14 '18 at 10:59

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