This article comes from the journal Science et Avenir – Les Indispensables n° 205 dated April/June 2021.

As soon as they are produced, our food begins a rigorous process of decomposition under the influence of microorganisms, oxygen or light. The challenge raised by human genius in various ways, starting with summer.

The tin can was born at the same time as sterilization

Cooking kills germs. As for dehydration, it inhibits the growth of microorganisms in the water contained in the food. The treatment of meat by drying would be attested 50,000 years ago, at the Pradales (Charente) hunting station, where bite marks were found on the bones of reindeer slaughtered in quantity here by Neanderthals. Dehydration can also be achieved in brine, dried or salted water, or by sugar that binds to water molecules. The result is confectionery, sour herring and other hams.

Another preservation process is smoking, which combines dehydration with the action of antimicrobial and antioxidant substances present in the smoke. In the 19th century, confectioner Nicolas Appert’s techniques were added to these secular techniques: he then tested the preservation of foods cooked in airtight glass containers, soon replaced by tin cans immersed in boiling water. Tin was born at the same time as sterilization (between 100 and 150 °C). The pasteurization method will be between 62 and 88 °C, which makes it possible to reduce the amount of microorganisms without excessively denaturing the food.

Freezing stops the enzymatic action of yeasts and molds

It is also well known that there is protection from cold. Preservation has been practiced in wells, caves or ice for thousands of years. Ancient Rome was already stocking up on blocks of ice extracted directly from glaciers. Always cold, freezing at -20 °C stops the enzymatic action of yeasts and molds as well as the oxidation process. But gradually freezing, the water contained in the cells of the food forms large crystals that eventually break them, deforming the products. Deep freezing has made remarkable improvements in this area.

Inspired by the practices of the Inuit, it involves keeping foods at -40 °C or -50 °C for between five and fifteen minutes to prevent frozen crystals from developing. Lyophilization adds to this rapid solidification by the elimination of interstitial ice by sublimation, i.e. cold drying. These recent preservation processes have marginalized fermentation, which is as old as cooking. This process often occurs without oxygen and allows microorganisms to convert food through the action of enzymes.

Cutting-edge technologies have not been abandoned

In addition, some storage methods also promote the preservation of food. In silos and cellars, minimally perishable foods can be stored for several months when temperature, light, humidity and oxygen levels are under control. State-of-the-art techniques have not been abandoned, such as irradiation, the elegantly renamed ionization, which is subjected to gamma radiation or a very high energy electron beam to destroy microorganisms and prevent ripening and germination.

Nanoparticles, for their part, can be found in food and containers. Thus, the EU-funded Nanopack project has made it possible to develop plastic films with mineral nanotubes that release antimicrobial essential oils into the packaging, slowing oxidation, humidity changes and microbial growth. The result: mold-free bread for three weeks.

by François Folietta