For chemical engineer Tonghan Gu, a typical day of fieldwork in Mumbai, India, begins not in a lab, but with a visit to Shree Char Bhuja Dairy. The clerks at this small shop in the city’s northern suburbs are friendly, if slightly puzzled, as they handle his request for 10 one-liter pouches of milk. The daily transaction takes only a minute or two, but it is part of a project that seeks a lasting impact in the fight against child malnutrition.