FWIW, the new Titanic Plum Porter cans have an ingredient list as follows :
INTERNATIONAL BITTERING UNIT
Water, Malted Barley, Wheat Malt, Malts ; Maris
Otter, Pearl Wheat, Dark Crystal, Hops ;
Pilgrim, Hercules, Goldings, Celeia,
Natural Plum Flavouring, Yeast.
That's how it is laid out - I suspect the text was designed for a different layout, then they changed it so the lines aren't right. The use of semi-colons is a little random, and I think there's a comma missing - what they're saying is that they use the Maris Otter and Pearl varieties of barley, plus malted wheat, rather than pearl wheat (which is a thing, it's dehusked like pearl barley).
Presumably Pilgrim and Hercules are used for bittering.