The Chemistry Behind Food Preservation

I am sure that most of you out there have some type of meat or grain-based products in either your refrigerators or freezers, just waiting to be consumed in a few hours, days, or even weeks.  Believe it or not, you actually can keep meat and grains from spoiling without using a refrigerator.  Ancient methods used to preserve meat and other perishables such as bread include smoking, salting, pickling (also known as brining), drying, and fermenting.  In this post you will see exactly how the chemistry behind food preservation allows such magic to happen.

Smoking

The first process we will look at is smoking.  Used in conjunction with traditional meat curing, smoking does not involve extremely high temperatures and is a very effective method of preventing bacteria from spoiling the meat.  Basically, the process involves a smoke room where heat indirectly reaches the meat through different types of wood.  This slow heating process causes the meat to dehydrate as well as accumulate a thin layer of smoke on the meat.  The smoke itself acts like an acidic coating that prevents most bacteria from growing.  In addition, the dehydrated meat also creates an inhospitable atmosphere for the bacteria that do manage to survive, slowing their growth immensely.  Some common examples of smoked foods are bacon and ham, all foods you have probably eaten at a dinner.

Curing

Another process that preserves food is curing.  Highly popular amongst meats such as pork and beef, curing is split up into two categories: salting and pickling.  Each of these has their specific purpose, varying slightly in their chemical approaches to curtailing the meat from spoiling.

pickling-jars.jpg

The first and foremost of these, salting is, just as its name suggests, a process that involves salt.  Specifically, it uses salts such as sodium nitrite/nitrate and potassium nitrite/nitrate to dehydrate the meat.  The way it does this is through osmosis.  This brings us to the second stage of the curing process, pickling.  The meat is immersed in a highly hypertonic solution of salty water.  The osmotic pressure acting on the meat’s cells cause the cells to shrink and release water, therefore dehydrating the meat.  Through the dehydration and osmotic pressure established in an anaerobic environment, the oxidation process for the meat is slowed down, thus prevented from spoiling.

While smoking and curing are to methods catered toward preservation of meat, there are additional methods for preserving other members of the food groups. In the case of wheat and other grains, for example, two completely different methods exist for preservation: fermentation and regular drying.

Fermentation

Fermentation is the process of converting sugars and other carbohydrates into alcohols, carbon dioxide, or organic acids by using different microorganisms under anaerobic conditions. Typically, yeast or bacteria can be used to make the chemical changes.  In the case of bread, for example, fermentation is used to leaven the bread and make it ‘puffy.’  When specific grains are fermented, however, substances such as alcohol can be produced and used in a variety of ways, from beer to vodka to medicinal alcohol (rubbing alcohol).  Wine is also a product of fermentation, as it contains alcohol as well.  Particularly, wine has an incredibly long shelf-life, lasting anywhere from a few years to several decades.  Most importantly, however, the process of fermentation actually enhances the foods with essential amino acids, proteins, and vitamins.

Drying

There are several kinds of drying techniques that dehydrate food, among which is smoking, as mentioned above.  However, the remainder of these techniques have to deal with the direct evaporation of the water from the food.  Since the food-spoiling bacteria and fungi need water to thrive, the absence of it will highly decrease their presence in the food and therefore lengthen the amount of time the food will be fresh for.  Farmers, for example, use drying to lengthen the amount of time they would need to sell all their grain. Freeze drying, another way to preserve foods, is also a very ingenious process that utilizes the properties of phase diagrams.  According to a phase diagram, water can sublime when it is under very low pressures.  A huge advantage freeze-drying has over the other drying procedures is that it does not utilize high temperatures to dry the food. In some cases, raising the temperature could chemically alter the food and make it inedible.  Also, freeze-drying foods and sealing them in protective bags can lengthen the shelf-life of food for several years.

h2o_phase_diagram.jpg

Summing It Up

In the end, several methods of preserving food other than refrigeration or freezing exist and work when the chemistry behind each is revealed.  Many of these processes were invented thousands of years ago and happened to work effectively enough to still be used today.  This is good to know because in the case of some kind of emergency where there is no electricity to keep the food from spoiling, there are working alternatives to save the food.  So, what will you do when the lights go out and the refrigerator stops working?

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