Milk car

Milk cars are a specialized type of railroad car intended to transport raw milk from collection points near dairy farms to a processing creamery. Some milk cars were intended for loading with multiple cans of milk, while others were designed with a single tank for bulk loading. Milk cars were often equipped with high-speed passenger trucks, passenger-type buffer plates, and train signal and steam lines seldom found on conventional refrigerator cars.

Milk has long been a staple food of agricultural societies. Fresh milk sours quickly if kept warm. Railways were used as early as 1840 to rapidly transport fresh milk from farms to cities. Early milk transport was in covered, tin-plated steel cans containing about 10 U.S. gallons (38 liters; 8.3 imperial gallons). Passenger trains typically offered the fastest service, so milk cans might have first been loaded into baggage cars. A farmer would adjust his herd milking schedule to have the milk cans filled shortly before scheduled arrival of the train. When multiple farmers required shipment, a separate car might be carried by the train specifically for milk cans; and that car could be delivered directly to the creamery to minimize time required for intermediate handling of the milk cans with other baggage. Once the handling advantages of a separate car were recognized, milk cars were built with insulation to reduce warming during transit and the milk cans might be packed in ice during warm weather. A few milk cars were built or retrofitted with mechanical refrigeration following World War II.

Increased availability of motor vehicles after World War I encouraged bulk transport of milk to minimize inefficient handling, washing and redistribution of milk cans. A standard 46.5 US quarts (44.0 L; 38.7 imp qt) milk can weighed 27 pounds (12 kg) and held 86 pounds (39 kg) of milk. Farmers needed two sets of milk cans so one might be filled while the other was at the dairy. Early milk cans had been soldered from three pieces, but they were later replaced by rolled and molded single-piece cans, which avoided uncleaned cracks in the solder joints. Milk tank cars were first made of glass-lined steel, and later of stainless steel. These tanks were often enclosed for insulation within a car body resembling a boxcar. These tank cars were usually filled with milk pre-cooled to 38 °F (3.3 °C) at a central collection point just prior to pickup by a milk train with a delivery schedule avoiding need for additional cooling during transit. Milk was shipped from Wisconsin to Florida as a test; and the temperature rose only a single degree (0.56 °C) during a trip lasting 101 hours.

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