lu·pu·lin
ˈlo͞opyəlin/
noun

1. a bitter, yellowish powder found on glandular hairs beneath the scales of the flowers of the female hop plant.

See that yellow stuff on the hop cone?  That's lupulin!  It is the substance that gives beer its delicious and distinctive aroma. Seeing, and smelling, this substance is one indicator that plants are getting closer to harvesting. 

Technically, all of the cones that we harvest are from female plants. Occasionally a stressed plant will produce some male flowers, but all of the plants in our fields are females.