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Old 11-13-2009, 04:27 PM   #1
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Default High Sugar Concentration Inhibits Bacterial growth?

I couldn't find a thread on this subject.

I am wondering chemcially or mechanically why bacteria can not grow in high sugar concentrations such as honey, and wine concentrate. As soon as you add water though, the bugs can go to town. Is it wrong pH? Or is it something else.

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Old 11-13-2009, 05:08 PM   #2
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Osmotic pressure.

The sugars will attract water to some degree, in an effort to balance out the concentration of sugar between the inside of the bug and the outside of the bug. Since honey is only about 30% water (IIRC) then that means pretty much all of the water from the bug gets sucked out and it implodes.

Once you get the dilute the sugars into a proper mix (70% water or so) then there isn't a whole lot of pressure trying to make the bugs implode and they can use the sugar as fuel.

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Old 11-16-2009, 10:01 PM   #3
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Quote:
Originally Posted by TimWeber View Post
As soon as you add water though, the bugs can go to town.
You've answered your own question. The previous poster has given more details. It's the same reason why salt was historically used to preserve foods.
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Old 11-16-2009, 10:06 PM   #4
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Quote:
Originally Posted by BigEd View Post
It's the same reason why salt was historically used to preserve foods.
and kill slugs
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Old 11-16-2009, 10:15 PM   #5
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Quote:
Originally Posted by whatisitgoodfor View Post
Osmotic pressure.

The sugars will attract water to some degree, in an effort to balance out the concentration of sugar between the inside of the bug and the outside of the bug. Since honey is only about 30% water (IIRC) then that means pretty much all of the water from the bug gets sucked out and it implodes.

Once you get the dilute the sugars into a proper mix (70% water or so) then there isn't a whole lot of pressure trying to make the bugs implode and they can use the sugar as fuel.
Positive on that answer?

Isn't it result of water activity? Sugar binds water by hydrogen bonds and even though there is water in a product, there is not any free water for other reactions.
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Old 11-16-2009, 11:18 PM   #6
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Quote:
Originally Posted by dfohio View Post
Positive on that answer?

Isn't it result of water activity? Sugar binds water by hydrogen bonds and even though there is water in a product, there is not any free water for other reactions.
At least fairly positive.

I'm sure there are a lot of reasons why a very high sugar concentration will inhibit growth, availability of water for chemical reactions being one of them, but osmotic pressure was the one I was taught in school.
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Old 11-16-2009, 11:24 PM   #7
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Default Honey has antibacterial properties

Just do a quick google....
http://www.worldwidewounds.com/2001/...cal-agent.html

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Old 11-17-2009, 12:25 AM   #8
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Quote:
Originally Posted by whatisitgoodfor View Post
At least fairly positive.

I'm sure there are a lot of reasons why a very high sugar concentration will inhibit growth, availability of water for chemical reactions being one of them, but osmotic pressure was the one I was taught in school.
Interesting...

I'm being taught that it is water activity
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Old 11-17-2009, 12:58 AM   #9
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It is water activity. However, a low water activity level (aw) does create an osmotic imbalance.

Water activity level is a common term in microbiology and food safety. It essentially means the water that is available in the food to be used by microbes. Here is a good definition I found:

Quote:
The water activity (aw) of a food is the ratio between the vapor pressure of the food itself, when in a completely undisturbed balance with the surrounding air media, and the vapor pressure of distilled water under identical conditions. A water activity of 0.80 means the vapor pressure is 80 percent of that of pure water.
It is actually one of the criteria to determine if a food is considered "potentially hazardous" (for simplicity, let's say that means it requires a controlled temperature such as refrigeration). If a food has a water activity level of below 0.85, it is considered non-potentially hazardous.

A good example of a type of food that can span the range of potentially hazardous to non-potentially hazardous is cheese. Hard cheeses such as Parmesan have water activity levels below 0.85 and do not require refrigeration. Soft cheeses such as mozzarella have a water activity level over 0.85, so they require refrigeration.

Jambs, jellys, syrups, etc. and anything with a high sugar concentration have water activity levels below 0.85 and don't require refrigeration. That's why they're on the shelf and not in the cooler at the supermarket.
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Old 11-17-2009, 02:09 AM   #10
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That, and most are also full of preservatives or have very low pH.

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