The cold chain is the continuous refrigerated handling of perishable foods from harvest to consumption. Breaks in the cold chain (food warming, even briefly) accelerate spoilage and can create food-safety risks.
For small farms, cold chain is one of the bigger operational challenges when scaling beyond the farmers market: you need reliable refrigerated trucks for deliveries, walk-in coolers for holding, and chef relationships that understand and respect delivery windows. Many farms that can sell at a market struggle to sell wholesale simply because their cold-chain infrastructure isn't there.