I used to do a concept called coverage for that. But.... splinterz didnt like it nor was it as self explanatory as ratio. U need to give higher ratios to those labors and maybe more jobs per dwarf. It will accomplish constant production if done right.
Before, each labor would have an associated attention cost. So no dwarf could have more than a sum of 1 attention cost in total labors assigned to him.
In your case, you would have had your brewer at 1 attention cost.
I changed the formula around so instead of assigning costs to each labor (and having to guess what each labor should be), it's setup using ratio's. So you can kind of think. Each labor would then have an attention cost of (Ratio of Labor / Sum (or is it average?) of Ratio's) * # of Labors to assign to each dwarf (or something to that affect). If I have to, I'll look it up, but this has been discussed in the old DT thread quite extensively (or has it... it might just be emails).
The math came out the same. It just ensures that you have proper "coverage" by ensuring you have a high enough ratio to ensure you have a dwarf always around to do that job.
The only other way around it, is to assign those labors exclusively and outside of the labor optimization plan (I've done this before for miner's). Or, what else I've done, is deselect all miner's from hauling, where-as the rest of dwarf's would have it enabled (who also had labors).
What also works is using autolabor JUST FOR HAULING labors, and don't assign any hauling inside DT.
Anyways, this tool doesn't do what your seeking due to pain in the ass implementation of such methods, but trust me, Splinterz and I have gone over this, and I was pushing for what you wanted, and he was kind of wanting an exclusive labor concept, but we/he decided ratio's works just as well, and manual deslection of exclusive dwarf's is a good workaround (that's how I do my nobles/militia)