English Wikipedia has an article on:

blackstrap

Wikipedia

From black +‎ strap? Possible connection with Dutch stroop (“syrup”).

• Audio (General Australian):

  (file)

blackstrap (usually uncountable, plural blackstraps)

1. The dark, viscous molasses remaining after maximum extraction of sugar from raw sugar cane, used in manufacturing and cattle feed.
   • 2007 July 25, David Hochman, “For Epicures, a New Take on Jerky”, in New York Times‎^[1]:

     Smoked over cherry and mesquite wood, and dried in a convection oven, it gets its flavors from organic blackstrap molasses, Jim Beam bourbon, and salt and pepper.

2. (obsolete) A mixture of spirituous liquor (usually rum) and molasses.
   • 1845, Sylvester Judd, Margaret: A Tale of the Real and the Ideal, Blight and Bloom; Including Sketches of a Place Not Before Described, Called Mons Christi:

     No blackstrap to-night; switchel, or ginger pop.

3. (obsolete, nautical, slang) Bad port wine; any common wine of the Mediterranean.