My resource for food shelf life is usually stilltasty.com . However, I can't find hot chocolate on the list. I'm talking about a small pot of hot chocolate - milk, cocoa, sugar, water. Is the guideline the expiration date of the milk? Or will it last longer/shorter?
2 Answers
It is a common misconception that the shelf life of a cooked food (= mix of ingredients) is the same as the shelf life of the shortest-lived ingredient. I cannot stress enough how wrong this assumption is.
As with any cooked food, the shelf life of hot chocolate should be about 3 to 5 days in the fridge, with a cumulative stay in the danger zone of no longer than 2 hours.
An explanation of why the assumption is wrong: Food spoils when bacteria (or sometimes other organisms like mold) create a colony in it. For this to happen, the food has to offer all the conditions an organism needs for survival. Most cooked foods are nutritious enough to ensure the survival of simple organisms.
There are single ingredients which hold for longer. Bar chocolate is a good example. The reason for that is that they are not a complete medium. Chocolate does not have enough moisture for bacteria to grow in it. But as soon as you mix any ingredient with something else, you cannot know if the other ingredients have not added the factor the bacteria have been missing. So, if you mix for example water (practically indefinite shelf life because it has no calories) and flour (practically indefinite shelf life because it has no moisture), you get dough, which will have large bacterial colonies within 3 days.
Exceptions in the other direction (food that spoils sooner than 3 days) are foods which decompose on their own. For example fish - it goes bad quickly even at fridge temperature, but the reason is the fish's own enzymes, not bacteria. That's why it is normally held on ice, if not frozen outright.
As a side note, you cannot rely on the expiration date of milk anyway. It is OK for traditionally pasteurized milk. But the expiration date of ESL and UHT milk is only valid as long as the packaging has not been broken. Once you open it, it is again good for about 5 days.
Conclusion: For anything cooked, up to 5 days in the fridge is a good assumption. Make it less for food which is known for high risk of contamination (e.g. food containing raw eggs), but never longer, even if the expiration date of the ingredients is longer than that.
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Where's you get the five days for milk as soon as it's opened from? I don't think I've heard that before. StillTasty says usually a week past the sell by date - obviously oversimplifying, but still. We also have a lot of vague answers here but if there's a consensus, it's probably that you should just smell/taste it.– Cascabel ♦Commented Jun 18, 2013 at 14:28
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@Jefromi As mentioned, she meant UHT milk, stilltasty.com/fooditems/index/17690– MienCommented Jun 18, 2013 at 15:58
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@Mien Oh, right. I was confused by the first part, saying you can't rely on the expiration date - in the US, UHT milk is much less common than in Europe, and you pretty much can rely on the date.– Cascabel ♦Commented Jun 18, 2013 at 16:35
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The only UHT dairy I can think of off hand here is those horrible little portion control creamers like fast food restaurants use.– SAJ14SAJCommented Jun 18, 2013 at 17:10
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2@jefromi I got this information for both UHT and ESL milk from a TV report, so I cannot link a written source. The report was of the trustworthy journalism type, and the person saying this was representing a professional association of milk producers, so I hope they knew what they were talking about. Besides, both ESL and UHT are thermal processes which work by killing the bacteria present in the milk, they don't make it poisonous to new bacteria. Once the milk gets exposed to new pathogens, they grow at their usual rate. So the 5 days make sense, even if we don't trust the source.– rumtscho ♦Commented Jun 18, 2013 at 19:17
You can still use the prepared food rule (~4 days in fridge, 2hrs at room temp). You can go with expiry of the most perishable IF the other ingredients don't have a spoiling effect on it (in this case, the effect is not significant). So the question somewhat reduces to how long does previously warmed milk last?
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If it's left at room temperature (in the danger zone 40F-140F), then the answer to How do I know if food left at room temperature is still safe to eat? applies.
If it's in the fridge, then a few days (~4) is the guideline. Have a look at Expiration Date on Milk.
If it's pasteurized and unopened, the expiry date is the indicator (usually a couple of weeks depending on the type of filtration).