(CBSNews) - Late summer marks the start of a critical time period for the 40 percent of Americans who enjoy wine: harvest season. Between August and October, about 4 million tons of grapes nationwide are processed on their way to the bottle. 

In the U.S., that job is mostly done by foreign workers. Vineyards, orchards and farms have long relied on guest workers to plant and harvest food. Federal law allows for these workers, who come through the H-2A visa program, to stay up to 10 months in a year.

Barboursville Vineyards, which has a reputation for producing some of Virginia's top wines, has relied on foreign workers for 20 years, hiring up to 16 every season, CBS affiliate WCAV reports.