Although cows were probably always kept on the ranch to supply fresh milk and butter, commercial dairy production began only after Richard W. Smith bought Sahuaro Ranch in 1927. At first the Smith family sold only bulk milk. The cows were milked in the dairy barn, built in 1928, and the milk was shipped to local dairies in cans. In 1932, under the supervision of Smith's son, Richard S. Smith, a retail dairy was established on the ranch and this milk house was built. Milk was first pasteurized to kill bacteria by heating the raw milk with steam from a boiler outside the building. After refrigeration in a large built-in cooler, containers of milk were carried to the pour room and drained into the separator below, which divided the liquid into milk and cream by centrifugal action. The dairy barn and milk house remain virtually unchanged since the late 1940s, when the Smiths stopped producing milk and closed the dairy. The pour room atop the exterior stairway was once moved away from the milk house, but it was reattached when the buildings were restored in the 1990s.