The War To End All Rot

An image of various rotten fruits.

Every time you reach into your pantry for a jar of pickles or a can of soup, you are benefitting from a process discovered by your ancestors: food preservation. For hundreds of thousands of years, humans have engaged in a battle against an invisible foe: the microbe. When left to their devices, harmful bacteria, molds, and yeasts can infiltrate our food supplies and leave us vulnerable to infections and severe health conditions. Although the risk of food contamination is always present, developments in both preservation and medicine have allowed humans to live significantly longer than they did for millenia.

The strategy to keep our food fresh does not require the spells used in ancient Egypt to prevent food poisoning or the rituals of European dairy maids who stabbed hot iron pins into sour milk to burn the “witches” they blamed for curdling. Instead, our methods are rooted much more in science and are unfortunately much less cool. Thanks to Louis Pasteur’s breakthroughs in the nineteenth century, we now wage a highly calculated war against the sneaky microbes trying to conquer our foodstuffs. In lieu of hexing them, we simply sabotage their survival: we starve them of oxygen, drown them in acid (and alkaline) baths, subject them to extreme temperatures, and deprive them of water. Bacteria (e.g., Salmonella, Clostridium botulinum) and fungi (e.g., yeasts and molds) are living organisms and just like humans, they require a strict set of conditions needed to grow, reproduce, and consume resources. Food preservation at its simplest level is executing one or more of the aforementioned techniques of sabotage.

The earliest form of food preservation was dehydration and it emerged across civilizations worldwide as early as 12,000 years ago. Our forebears were pre-modern scientists in a way. Hunter gatherers realized that meat and fruit left out in the sun dried out and lasted for longer. This empirical observation was key, as it meant that these nomadic humans could travel whilst keeping food on hand, facilitating their survival if resources were scarce in some areas. While most other civilizations utilized heat to preserve their foods, Andean peoples left their potatoes out in the extreme cold of the night, creating the first freeze-dried food – chuno. Dehydration was the first step to humans being able to establish permanent settlements, but what’s the science behind it? 

A platter of dehydrated fruits.

Dehydration works by stripping microbes of free water, which is necessary for their survival . When moisture is removed, microbes that come into contact with the dried food are sucked dry of their water supply, causing its cells to shrivel. Without a stable shape, the microbe’s vital enzymes unravel, paralyzing its metabolism, and neutralizing its ability to secrete toxins responsible for food spoilage.

While dehydration remained the global standard for preserving grains and fruit, it was overshadowed by salting when it came to preserving meat and fish. Pure sun-drying had major limitations as fats in thick cuts of meat often degraded before preservation was completed, rotting them from the inside out. 

An example of a cut of meat being submerged in salt to dehydrate it.

Around 6,000 BCE, ancient Chinese and Egyptian civilizations solved this problem through a similar but chemically reliant process known as salting. When high concentrations of salt envelop food, water molecules migrate out of the cells to balance solute concentrations across cell membranes. This effectively dehydrates the food, depriving harmful microbes of the moist conditions they need to reproduce and sustain life, preventing them from releasing enzymes that break down macronutrients.

While dehydration and salting eliminate moisture, a later historical discovery accomplished something that its predecessors could not. Around 2,400 BCE, ancient Mesopotamians began soaking foods in acidic liquids, a practice we know as pickling. Most food-spoiling bacteria thrive in environments with a neutral pH. When they are subjected to a highly acidic environment (one below 4.6 pH), excess hydrogen ions in the acid (usually vinegar or salt brine) break the molecular bonds holding microbial proteins together. Unlike dehydration though, once the food is re-exposed to moisture, it doesn’t spoil immediately; instead the acidity leaves a shield that preserves the freshness, texture, and nutrients of the produce. 

A challenge with a reward of 12,000 francs is the reason why we have canned goods today. In 1795, Napoleon Bonaparte needed a reliable way to preserve military rations and the only person to configure his solution was French chef Nicholas Appert. It took him fourteen years to perfect his method but in the end, he left us with “appertization” – packing foods into airtight containers, sealing them tightly, and boiling them for hours. The intense heat causes microbial proteins to lose their shape, killing all microbes within the container. 

Various canned goods preserved through appertization.

Pasteur used this same exact science of microbial destruction through heat but tweaked it to protect the delicate nature of liquids like milk. While Appert boiled his jars for hours at 212 degrees fahrenheit, Pasteur heated milk for just fifteen seconds at 161 degrees fahrenheit. His method applied just enough energy to destroy dangerous pathogens without curdling the milk.

While canning, salting, pickling, and dehydration successfully kept food from spoiling quickly, none of them could preserve food in its pure, natural state. The invention of the refrigerator has proved to be one of the most important advancements in technology. Refrigeration lowers the temperature inside of microbes and reduces the energy they need to collide and catalyze biochemical reactions (spoilage). Freezing takes this one step further and completely, well, freezes, microbial metabolism. 

Food bridges the gap between us and our ancestors and the story of its preservation allows us to further our understanding of human life and death. For thousands of years humans were entirely at the mercy of nature where one bacterial outbreak or an area scarce of resources could result in the starvation of entire civilizations. Fortunately for most of us, food is no longer a fuel source used just to keep us alive through winter; instead, it has been transformed into a vessel for community and comfort, warming our bones and hearts through every season.