Many cheeses with a long shelf life are produced by lactic-acid fermentation. Today it is hard to understand how precious salt was in ancient times, when it was valued partly as an effective preservative. Salted herring were exported in large quantities from North Sea fishing communities and consumed throughout most parts of Middle Europe. During the Middle Ages the winter feeding of livestock was often so difficult that only animals selected for breeding were kept alive. Meat from the slaughtered livestock was salted for consumption over the winter.
Smoking is another ancient and common means of chemical food preservation.
Smoked foods include bacon, kippered herring, and lox. Permitted levels of such antioxidants as additives are far below levels found in smoked meat. But native South Americans living on the Altoplano, in the Andes, have subsisted on freeze-dried potatoes of a sort for thousands of years. The plateau dwellers carry the potatoes up into areas where the atmospheric pressure is very low, the sky is usually almost cloudless, and the nighttime temperatures fall well below the freezing point of water. When Animalcules Attack Anthropologist Loren Eisley has attributed the human population explosion to the invention of the microscope, before which understanding of endemic diseases had been impossible.