The Effects of Water on Food Stability


As I continue to study, and practice, various preservation techniques used by pre-1600 peoples, there is one key bit of information that many people seem to forget. That fact being that water isn't shelf-stable, and can't be preserved without substantially changing it.

Water in Preservation

"Wait!" I hear you say, "Pickles are kept in salt water, what's the deal with that?"

To that, I would respond with the fact that pickles are in *salt* water. This is different than pure water. The addition of salt alters the chemistry of the water, making less hospitable for pathogens.

This is because a portion of the water molecules are tied up with keeping the salt in suspension, with the remaining molecules being available for biological enzymatic and chemical reactions.

This measure of available water molecules is known as "water activity".

Foods with low water content, such as crackers or hard cheese, have a lower water activity compared to something like fresh meat.

Controlling Water Activity

Water activity can be controlled in a number of ways.

First is to dry the good in question. This is often done using a dehydrator, or a smoker over the course of several hours.

A second method is to introduce something like salt to lower the water activity, but maintain a liquid that is safer in the long term. Sugar can also be used to reduce water activity, but presents its own issues with bacterial/fungal growth.

Preserving Water?

With all that being said, you may wonder if it's possible to preserve water.

For extended period of time? Yes, but no.

Water drawn from sources, such as the faucet at home, is generally filtered to some degree, and will keep for a time, but will not be stable on the order of years. This amount of time would give any microbes, pathogens, etc., time to grow in number. In the case of tap water, even months can be enough time for pathogens to take hold, under the right circumstances.

Bottled water is in the same camp, but because of the extra filtration, the shelf life is extended, but not indefinitely.

Water can be treated in ways to extend its longevity (filtering, UV purification, etc.), but these are not preservation methods as we tend to think of such things, because the water molecules are still mostly available for biological use.

Anything made with a significant amount of water, such as reconstituted cosmetics or dyes, are just as susceptible to bacterial and mold growth, and should be monitored for such.

Any signs (appearance, smell, etc.) of spoilage mean the good needs to be disposed of. With the exception being the presence of intentional "spoilage" such as beneficial molds, as they are just that, intentional.

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