(WB) - Large wineries, most notably Constellation Brands and Treasury Wine Estates, are now exercising the option to skip a vintage with many growers. They’ve been rejecting a significant share of the wine grapes they source from Lake and Mendocino counties, two counties hit by wildfires this summer, according to industry sources. The amount of fruit that has been rejected over possible smoke exposure is unknown at this time, but it appears to be quite substantial.

Last year, California’s North Coast harvested $1.5 billion in grapes.

It's a difficult situation. There is no clear definition of "smoke taint" and there's only a partial understanding of the chemistry involved. The concern about smoke exposure also comes as the industry is poised for a larger-than-average harvest and at a time where there's already limited demand for bulk wine and grapes.

Constellation Brands is one of the companies that have been turning down fruit from Lake and Mendocino counties, according to multiple sources interviewed this week. Notices have been sent to Mendocino County growers in Potter Valley, Redwood Valley and Ukiah.