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After all it has oil and sugar in it. Why doesn't bacteria love it? Thanks!

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I'm only 11 and I am doing a science experiment and I need to find out if it goes bad and how long does it take to go bad and stuff like that. So if you could please word these answers a bit easier for me to understand these amazing answers I could really use:) –  ruby Aug 17 at 9:20

7 Answers 7

up vote 13 down vote accepted

Simple: it has no water.

Chocolate is a suspension of cocoa solids and sugar in cocoa butter. It is made from fat and carbohydrates only. Bacteria, as everything else, need water to live. They can't survive in something hygroscopic (like jam or honey) or something with no water at all (flour, chocolate, pure fat). Similar for molds. So, independent of temperature, chocolate won't go bad in the sense that it will never grow colonies of bacteria.

As Hobodave mentioned, it can "grow bad" in another sense. If held at high temperatures (somewhat above 30°C), the chocolate butter will separate from the mix and form a dull yellow-grayish crust on the chocolate surface. Also, if you leave it in contact with oxygen for long enough (many months), the cocoa fat will go rancid. In both cases, it is perfectly safe to eat the chocolate without risking food poisoning. However, the taste is much worse than in normal chocolate.

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The scientific term for this is "water activity". See my answer on Skeptics SE about the spoiling of honey. –  nico Mar 12 '12 at 19:50
    
Bacteria can survive without water, but they won't be active, won't multiply and won't be able to do any damage to the chocolate. –  Jacek Konieczny Mar 13 '12 at 9:03

It does go bad.

The shelf life of opened dark or bittersweet chocolate is one year. Milk chocolate lasts only about eight months, due to the presence of milk.

The reason it has such a long shelf life, even opened, is due to the cocoa butter. Cocoa butter is a fat, but it is primarily a saturated fat, and thus is solid at room temperature. Saturated fats are naturally less susceptible to degradation than unsaturated fats (oils). Cocoa butter acts as a preservative in chocolate, as well as in cosmetics.

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So why is cocoa butter a preservative? –  Adam C Sep 15 '10 at 17:57
    
It is high in antioxidants. Oxidation causes fat to go rancid. wisegeek.com/what-is-cocoa-butter.htm –  hobodave Sep 15 '10 at 18:20
    
I wonder if that wisegeek thing is correct; I thought the antioxidants in chocolate are not in the cocoa butter fraction. However saturated fats themselves won't oxidize quickly because there is no place on them for the oxygen to attach (they are already saturated). –  Michael at Herbivoracious Sep 15 '10 at 18:45
    
@Michael: There are most certainly antioxidants present in cocoa butter. There are numerous other sources. –  hobodave Sep 15 '10 at 18:52
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@MichaelatHerbivoracious Saturated fats are not saturated with oxygen, they just don't have double bonds between carbon atoms in fatty acids, and thus are saturated with hydrogen. Molecules saturated with hydrogen oxidize nicely (e. g. methane, ethane). –  Mischa Arefiev Mar 12 '12 at 9:53

I'm not sure how big a factor it is compared to the other answers, but chocolate generally doesn't have water in it, and bacteria generally don't like water-free environments.

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Simple answer is that it does.

Most commercial grade chocolate (Cadburys and what have you) is full of various preservatives to keep it "fresh".

Also, higher quality chocolates will have less sugar in (as it will have more cocoa).

Its the same as bread - fresh, homemade bread will be spoiled in a few days, but supermarket bought stuff can last 7 days+

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Have you ever seen chocolate go bad? real chocolate not a candy that has chocolate in it. I have seen discoloration, but not spoiling of chocolate. –  Adam C Sep 15 '10 at 17:56
    
@Adam C - when oil goes bad it goes rancid. It shouldn't have the same impact as getting eaten by bacteria. –  justkt Sep 15 '10 at 18:01
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I have personally eaten milk chocolate that was over 30 years old; it had some white "bloom" (sugar crystallisation) on the surface but tasted perfectly fine and did not make me ill. –  Vicky Sep 16 '10 at 11:23
    
Oh also, it had not been sealed - it was loosely wrapped in paper. –  Vicky Sep 16 '10 at 11:24
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@mskfisher - when I was a kid, my Mum brought some old Christmas decorations down from the loft, they were left over from when she was a child herself. Most of them were glass baubles in various states of brokenness, but there were a few red paper Christmas Crackers which turned out to have small fingers of chocolate inside them. So I ate them! –  Vicky Aug 9 '11 at 14:09

Both cocoa butter and the dark solids in chocolate are high in antioxidants. There is also almost no moisture in "tempered" chocolate. When chocolate is tempered the cocoa butter part of the chocolate is crystallized, which helps the chocolate form a tight lattice-type structure. The combination of 1) a high percentage of antioxidants, 2) almost no moisture, and 3) a dense, tight crystalline structure results in a product that has an extremely long shelf life. I make chocolate professionally, from the cacao bean, and I have some bars (70% cacao) that I make over 3 years ago that have shown absolutely no degradation. They taste the same as when I first made them.

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I doubt that the antioxidants are a reason, they are probably inactive in the chocolate for the same reason that the bacteria can't live in the chocolate - not the right environment for the biochemical processes they are part of. But the rest sounds reasonable, especially the low moisture part. –  rumtscho Jan 23 at 19:30

Most commercial chocolate does not have a shelf life. Batches are dated for processing and tracking purposes but there is really no inherent limit to how long it will remain shelf stable assuming it remains below about 30C / 85F and in a correctly controlled environment.

Chocolates that contain preservatives typically do so because they contain non-chocolate fillings.

Most chocolate that goes "bad" is the result of 3 issues:

1) It was in an environment above 30C / 85F will begin to lose temper (above 35C and 95F for sure) and begin to liquefy. Once the temperature returns below these temps, the chocolate will resolidify but may take on a chalky white texture and color. Assuming it didn't get hot enough to burn, the chocolate is fine and while it may lack correct mouthfeel, it is perfectly fine to eat. This chocolate, if melted down and correctly retempered, will return to its original, crisp and shiny texture and color.

2) It was stored for a period to time along with other foods or items that have a strong odor. Chocolate is high in fat and as such easily absorbs flavors and odors.

3) Storing chocolate in a cold location and then introducing it to "room temperature" will cause condensation on its surface. This moisture will later cause a "bloom" on the surface and depending on the amount of moisture introduced and over what period to time, may be purely cosmetic or have an actual affect on the chocolate but it is difficult to say at what point it has actually gone "bad".

Storing your chocolate in a refrigerator or freezer is a poor choice for reasons 2 and 3. Years ago I had a friend that stored chocolate in a motorhome in which he smoked and he wondered why after 6 months it tasted like an ashtray?

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Chocolate must also have an anti-microbial factor because not only does pure, dark chocolate have an extremely long shelf-life but cakes made with high dark-chocolate content seem to last forever!

I've seen Trader Joe's Triple chocolate bundt cakes (NO perservatives) last over a month uncovered at warmish room temperature! Try that with any other natural cake or bread item... they get moldy in a week!

The only ingredient that they have different from other cakes is chocolate (and lots of it).

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I'm not sure if this really addresses the question. Cakes can last a long time for a variety of reasons. –  Jefromi Mar 12 '12 at 5:30

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