P. Ballantine and Sons apparently began marketing malt syrup at the turn of the century (see second ad, right, "Since 1900").
Used as a sweetener and yeast food in the baking industry, Ballantine would advertised their bulk-packed (in barrels) "malt extract" syrup heavily to the industry.
During Prohibition the product, now packaged in small cans, was much in demand by homebrewers. ("Hop flavored" varieties were obviously not being used for muffins.)
Dozens of brewers had added malt syrup to their product line with the outlawing of "real beer", with many of the large breweries (including leading brewers like Anheuser-Busch, Pabst, Schlitz and Ruppert, along with Ballantine), forming the "National Malt Products Manufacturers Association".
Ballantine's brands- Ballantine's, Federal (dark), Jersey (light), Three Rings, Checker, and Zone- were distributed nation-wide. Being a canned product, it could be easily shipped, stored and sold in such distant markets as Montana and Texas.
(above) CHECKER brand malt syrup