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The modern cold chain, an unbroken sequence of refrigerated storage and transport, transformed food markets by allowing perishable goods to travel far beyond their region of origin. Before refrigerated trucking and shipping containers became widespread in the mid-20th century, most produce sold in urban markets had been harvested locally within the past day or two. The cold chain removed this constraint, but it introduced a new vulnerability: any break in refrigeration, whether at a port, a warehouse, or a delivery truck, can spoil an entire shipment even if the failure lasts only a few hours. Food safety regulators now treat temperature monitoring as a continuous requirement rather than a periodic check, precisely because a single gap can undo weeks of careful handling.