How Food Spoils: Microbes and Oxidation

The following is an excerpt from Doctor Stillman’s online course, “Practical Wellness.” To find out more or to subscribe, visit

Food preservation is any process or practice that increases the period of time that the food will be edible. Fundamental to this process are two concepts. First, you have to prevent the growth of dangerous bacteria. Second, you have to prevent spoiling of the food through certain chemical reactions. Often, these objectives are one and the same.

To understand why food spoils, it is helpful to understand why it doesn’t spoil on the vine, in the ground, or while it is grazing out in the field. Any living organism has mechanisms to prevent its decay and enable it to survive and reproduce. Every organism has an immune system to fight off disease and repair injury. Once food is picked, harvested, or slaughtered, it slowly begins to decay.

Bacterial growth depends, like any organism, on the right balance of nutrients, temperature, acidity, and humidity or moisture (among other things). Altering any of these factors can preserve food. Salting food removes any water from it, soaking it in acid lowers the pH, which are just two examples of preserving food (covered in more detail below). Foremost, the bacteria must be present and able to reproduce. This is why canning can preserve food. The heat destroys any bacteria and the air-tight seals of the cans or bottles prevent any from entering.

Oxidation is the other process by which food spoils. When you bruise an apple, the air that suddenly can reach the antioxidants in its now damaged cells quickly turns those cells brown. The oxygen in water can cause iron to rust, which turns it from a dark, black or blue color to rust, which is brown. Many preservatives work by preventing oxidation.

Oxidation is opposed by reduction. Oxidation is the loss of electrons, while reduction is the gain of electrons. Oxidation and reduction are not just relevant to food spoilage, but to aging. Free radicals are one of the most important causes of aging. Free radicals are produced by oxidation. Major nutrients like vitamin C and vitamin E, whose health benefits are well known, prevent oxidation, and are called “antioxidants” for that reason.

Preservatives that work through oxidation and reduction may have different effects on food, microbes, and on the human body. Preservatives that work through oxidizing bacteria may also oxidize human cells, resulting in damage to cell components or even DNA, which is carcinogenic or cancer-causing.

Because preservatives are so heavily relied upon by the modern food industry, there is significant industry-sponsored science surrounding their safety, and relatively little data to balance it that comes from unbiased sources.

How do plants and animals prevent these processes from causing their flesh or fruit to rot in the field? They carefully separate their cells into different compartments and control the levels of oxygen, water, and ions in each. This is going on in each and every cell and organ of your body at all times. Microbes or oxidation can chew through these compartments and consume these nutrients. All organisms devote enormous energy to preventing oxidation and microbial invasion to prevent exactly this.

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