Kitchen Chemistry 104: Preserving Foods

I’m fascinated by the ways humans have learned to preserve foods.  Often, our forebears came up with methods first, and only later– usually much, much later– figured-out why it works.  In other words, humans did not reason their way to food preservation… they simply experimented their way… probably with horrible consequences for the ninety-nine out of hundred methods that they found did NOT preserve food (“Poor Uncle Gunter!– And he thought the moonlight would preserve that chicken…”)

We know now that spoilage comes when cells in foods begin to breakdown.  This breakdown causes, among other results, two things very relevant to food spoilage:  1) enzymes are released from the rupturing cells that can react badly with the outsides of the other cells of the food, causing food to taste and smell bad to us humans, and  2) on the other hand, those damaged cells are starting to look pretty tasty and smell pretty good to bacteria and their kin; the breakdown of cells in spoiling food encourages the colonization of the food by micro-organisms.

Preserving foods often works on the principle that water is required for life as we know it.  Take away a critter’s water source, and it will have a hard time surviving for long, much less thriving.  So, preserving is often about drying foods out.

One of the simplest methods is sun-drying.  Raisins, for example, use the sun-dried method.

The problem with the sun-drying method is that certain foods will spoil faster in the sun than they can dry out.  Fruits aren’t as problematic because as they dry-out, their sugars become more and more concentrated.  All this sugar has an osmotic affect on the water in the cells, pulling out the water from the cells, thus allowing the drying process to outstrip the spoiling process.

Fish and meat need a little more help.  Salt is often key.

When you place meat in a heavily salted mixture (a “brine,” as they say), the meat-liquid mix will attempt to achieve an equilibrium in which the saltiness inside the cell membranes of the meat is equal to that of the brine outside.  This means that the liquid inside the cell will rush out to water-down the overly salty liquid surrounding it (for membraney reasons, salt will not travel the other way, into the inside of the cell, so it’s a one-sided attempt at balance).  In other words, even though the meat is submerged in water– it will dry out.

This process affects mostly the outside layer of the meat, but that’s enough.  With its now dried-out surface protecting it, bacteria will have a hard time developing inside the meat.

After the brine has had time to do its work, one takes the meat out of the solution and dries it in the sun (in thin strips, I imagine).

There are other ways besides salt, of course, to preserve foods.  Simply cooking foods is one way to preserve them a little longer (high temperatures kill micro-organisms… also, heat can denature spoilage-inducing enzymes).  Relatedly, we’re all familiar with canning foods, in which foods are heated to kill off any bacteria, and then quickly and properly sealed so that no new baddies can get at them.

And then there’s good old fashioned refrigeration… Chilling foods slows down all the messy processes of life, death, and decay.

Another preservation method is the use of acids to create inhospitable environments for micro-organisms.  Most of the usual suspects causing illness prefer their pH at least moderately balanced.  The acid treatment is the method employed when one pickles foods.  It’s also part of the reason yogurt keeps so well.

And then there’s the Smokehouse treatment.  I’ve never actually seen a working model, but I have been inside defunct smokehouses turned into storage sheds.  They tell me that using smoke to treat foods not only heats the foods (slowing spoilage that way), but also coats the food with, as Field puts it, “substances that do not promote the growth of spoilage organisms.”

This may not sound appetizing, but the smoke does not penetrate very far into the food.  And I’ve actually had smoked ham and smoked turkey before, and found them both very satisfactory to the palate.


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