"Well-meaning people often have a hard time understanding what systemic racism looks like," music scholar John Vilanova wrote last year, after Taylor Swift beat Kendrick Lamar to the best album title.

"This is what systemic racism looks like."

He says black artists are sidelined into categories that are "coded black", like best urban contemporary album, which saw Beyonce win her 22nd Grammy, and best R&B performance, awarded to her younger sister, Solange.

Solange herself spoke out about Beyonce's loss on Sunday.

She tweeted: "Create your own committees, build your own institutions, give your friends awards, award yourself, and be the gold you wanna hold, my Gs".

The tweet was later deleted.

Music writer Kevin Powell suggested Beyonce's Lemonade - which tackles racial politics, police shootings and female empowerment - made voters "uncomfortable" because it is "unapologetically black".

"We are still a nation that does not want to deal so directly with truth," he told CNN.

"Adele's album is strong, but it is just songs about love. It is safe and uncontroversial; it breaks no new ground. And neither do Grammy voters, generally speaking, when it comes to picking winners of this particular award."