My experience (slim and dated though it is) tells me that malt is much less durable than the unmalted barley. I know that at least in San Francisco the barley came to one or more commercial malt houses (either independent of or internal to the breweries or distilleries) for malting right before delivery to the target businesses for making wort, fermenting, and the rest of the post-processing. If I were to model the business before the days of covered hoppers for grain, I'd show the barley at a malt house in bags and then drays carrying the malt syrup in something like large carboys across town to a customer
All malt houses that I know of provided dry malted barley.
None that I know off shipped liquid across town.
Now someone did process the malted barley and made malt syrup and dried malt.
During prohibition some of this was done by Pabst.