Fermentation was used to preserve food 10,000 years before refrigeration

Fermented foods — sauerkraut, kimchi, cheese, yoghurt, miso, sourdough, wine, beer, vinegar — are among humanity's oldest technologies, with evidence of fermented beverages in China dating to 7000 BC. Before refrigeration, controlled fermentation was the primary method of preserving food across cultures. The microorganisms involved — bacteria, yeasts, and moulds — not only prevent spoilage but transform nutritional profiles: fermented soy is more digestible than raw soy; sourdough's long fermentation partly breaks down gluten; fermented dairy becomes tolerable for some lactose-intolerant people. Modern research links fermented food consumption to improved gut microbiome diversity.

Source: Katz, The Art of Fermentation (2012)