A normal refrigerator is built to hold food that is already cold. Put a deep pot of hot dal or biryani inside and it cools slowly, warms everything else on the shelf, and spends hours in the range where bacteria multiply. A blast chiller is designed for the opposite job: it pulls heat out fast using a powerful refrigeration system and strong fans that blow very cold air over shallow trays.
A widely used benchmark for blast chilling is bringing cooked food down to around 3 °C at the core within about 90 minutes. Most units have a food probe that goes into the product and runs the cycle by core temperature rather than time, with soft-chill settings for delicate items and hard-chill settings for dense foods. Shallow GN pans and loose covering help the air reach the food.
A central kitchen in Gurugram supplying a chain of cafés might cook gravies, rice and curries in bulk each afternoon, blast chill them, then store them chilled for dispatch the next morning. Without a blast chiller, the same batch cooling in a reach-in would sit warm for hours.