I do have a even smaller barrel that was given to me by my sis n law. Maybe I will try/test the method of filling the barrel with only a fraction of bourbon, and then age our syrup in it after draining the bourbon.
I aged the 2.5 gal barrel with bourbon and I did fill it to capacity. But like I said that's not really a viable option due to cost to fill the barrel with bourbon.
I also was wondering about reusing the barrel again after re aging bourbon it it. But I think you would need to "clean" the residual syrup out of it first and then add the bourbon back into it. I would also be concerned that it may form mold inside the barrel with the sugars left in it. But the bourbon "should" kill any mold spores that form, as long as your consistently rotating the barrel.
There is definitely alot of science involved in the use of these barrels.
I will try the small barrel experiment and report back when we do it. Worst case scenario, I go back and try again. It's worth a try as like you said Dave, this is a very value added product to syrup production.