Not sure if you have abandon the idea already but i think there is a solution which is satisfactory for most:
Preservist are creating the “jarred” food.
How about adding a bit of randomness into the mix.
Preservist creates food from veggie/fruit + glass, that being carried to houses, people consume the item, then there is a 75% chance to return a waste jar.
Waste jar can be repurposed by the preservist, adding them something to do in the off-seasons where no fruit/veggie is available to preserve.
Basically adding a new recepie just to produce “glass” out of waste jars, using water + firewood (aka boiling)
Unsure how complicated it would be to program this, but this way, there would be more reason to use preservist jobs.
Obviously numbers can be tweaked, both in production and in % chance
P.s.
Just as Sean_Murphy said above