This is the second edition of “Why our Food Rots.” To get you up to speed, last week’s article described what causes food to rot: MICROBES! I also mentioned the basic methods of food preservation and that changing the temperature of a food can either slow the growth of microbes or kill them. This week’s article will describe how various chemical treatments help in preserving food. The means of preserving food and the chemicals used to preserve the food are as follows:
- pickling (salt or sugar; vinegar, a weak acid)
- fermentation (alcohol)
- chemical preservation (lots of compounds too long and hard to pronounce for now)
When people think of chemicals they usually think of compounds with long names that are poisonous to life. That is not really true. We are made up of chemicals. Salt and sugar are chemicals that are commonly found in our bodies. There are other chemicals that are not commonly found in us that can be deadly. Lead is a chemical that you don’t want in your body because it is very poisonous.
Unlike lead, chemicals like salt, and sugar are only poisonous in very very very high concentrations. Salt and sugar are also poisonous to microbes when in high concentrations. High concentrations of salt and sugar actually suck the water out of our cells and out of microorganism’s cells. When water levels get too low in a cell the cell will die because the enzymes in the cell can’t do their work. No enzymes working means no energy being produced. No energy leads to cell death.
There are a lot of examples of people using high concentrations of salt or sugar to preserve food. Beef jerky is one example. The meat is dried and salted to preserve it. Pickles are preserved in a salt brine that prevents the growth of microbes in and on the cucumbers. Vinegar is also used in salt brine to increase the acidity of the brine. Microbes are killed by acidic conditions because acid will also destroy the enzymes that make microbes grow. Jams, jellies and sweet pickles are examples of the use of sugar to preserve food.
These preservation techniques don’t kill us because we can lower the concentration of the salt or sugar by diluting them out with other foods we eat and because of the large mass of our bodies compared to the amount of salt or sugar we eat. Unfortunately for the microbes, their cell body mass is very small and as a result concentrations of salt and sugar that have little effect on us are deadly to them.