Entry in progress—B.P.

Wikipedia: Genmaicha
Genmaicha (玄米茶?, “brown rice tea") is the Japanese name for green tea combined with roasted brown rice. It is sometimes referred to colloquially as “popcorn tea” because a few grains of the rice pop during the roasting process and resemble popcorn. This type of tea was originally drunk by poor Japanese, as the rice served as a filler and reduced the price of the tea; which is why it is also known as the “people’s tea.” It was also used by those persons fasting for religious purposes or who found themselves to be between meals for long periods of time. Today it is consumed by all segments of society.

Tea steeped from these tea leaves has a light yellow hue. Its flavor is mild and combines the fresh grassy flavor of green tea with the aroma of the roasted rice.

Google Books
Japanese Cooking
By Susan Fuller Slack
Tucson, AZ : HPBooks
1985
Pg. 20:
Genmai-cha is sometimes called popcorn tea because it is a combination of bancha and partially popped brown rice. This tea is sometimes served in inexpensive restaurants.

,The Wall Street Journal
February 19, 2011
Tea’s Got a Brand New Bag
Chefs and bartenders are bringing the leaves out of the kettle and into the kitchen
(...)
Genmaicha
Tasting notes: Vegetal and nutty, with a toasty sweetness.
Kitchen trick: Grind with a pinch of sea salt to create an unexpected and adaptable seasoning for grilled vegetables and meats, says Melanie Franks, tea-chef and instructor at the French Culinary Institute.
Pantry pick: In Pursuit of Tea Genmaicha, $28 per ¼ lb,inpursuitoftea.com
Etc: Made from a blend of Japanese green tea and roasted, puffed brown rice, genmaicha is sometimes called “popcorn tea” thanks to its unusual appearance.