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I had a first try on a self-made recipe for a chocolate-hazelnut cream, in short Nutella.

Question Even though I used ingredients that wouldn't have gone bad singularly, the cream as a whole had an intolerable acid smell after 1 week from the preparation. What could have been the cause?

How the cream was prepared I prepared a chocolate-mousse only using 70% dark chocolate and water, then I blended it together with brown sugar, hazelnuts and olive oil. Immediately after preparation the cream was fine. Then I left it on a shelf, and when I came back after 1 week it had a strongly pungent acid smell, the taste was in line with the smell; the situation was bad enough to force me to throw everything away.

Thank you very much for your interest!

  • What makes you think water doesn't go bad on its own? – ElendilTheTall Nov 30 '14 at 15:35
  • Are you joking or am I missing something very basic? – Giovanni De Gaetano Nov 30 '14 at 16:26
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    Water does go bad, and causes things that don't go bad when dry to go bad through getting wet. – ElendilTheTall Nov 30 '14 at 16:35
  • Thanx!! Do you mean something like: "wet hazelnuts" (just to mention one) rot, while dry hazelnuts don't? Because I would say that water left in glass on a shelf at most evaporates or collects unwanted stuff from the environment, but doesn't deteriorate by itself. Am I right? – Giovanni De Gaetano Nov 30 '14 at 16:38
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This is a basic fact of food safety. It doesn't matter how long each of the ingredients take to go bad separately. Prepared food will go bad soon unless you do something special to preserve it.

In your case, you had hazelnuts, which don't go bad because 1) they have too little water, and 2) bacteria cannot enter their tissue, which is made of intact cell walls. You also had chocolate, which doesn't go bad because it doesn't have enough water for bacteria to survive in it. Ditto for sugar. Then you mixed everything together and added water, the one thing which was missing in order to keep bacteria out. And you also pureed it, which destroyed the protective cell walls. Bacteria found your food and started multiplying in it.

To address your comment too: water by itself doesn't usually go bad, because it has all the water a bacteria needs, but not nearly enough food content. So, bacteria cannot survive in it, at least for a short time. Were you to leave out a mix of water and carbohydrates out, you'd notice vigorous bacterial activity - this is what fermentation is. But there are some classes of bacteria which can survive on the minimal amount of debris caught by a water reservoire sitting around for weeks, and one of them is indeed pathogenic, causing a dangerous form of pneumonia. So, water does deteriorate, just not as quickly as the usual types of wet food, which are hospitable to many more pathogens.

In general, all human food is great food for bacteria, often including pathogenic bacteria. You have to take something away to make it inedible for bacteria. Any mixture of two shelf stable foods can turn out to add exactly what the foods separately lacked, and make it a bacterial breeding ground again. So, never assume anything about food shelf life based on the shelf life of its ingredients!

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    Thank you very much! Now that you explain it, it looks quite obvious; but it truly didn't cross my mind! – Giovanni De Gaetano Dec 1 '14 at 7:58

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