Some of the machines are prone to eat money. But in general the response has been strong. One machine placed outdoors at Villa Park High School in Orange County, Calif., was selling out on a daily basis before it shorted out in a heavy rainstorm. Chocolate is the favorite flavor everywhere, but tastes vary by market. Coffee-flavored milk accounts for about 30 percent of sales in Boston.
Plain milk is available in all the machines but typically is the least popular.
Low-fat varieties also are stocked.