The "potion" itself may best be produced through a reaction that produces a food item (like bisquits, but perhaps a new one named "potion") of a given material which is named for it's effects (So a recuperation potion is a "potion" food item made from recuperation-puddy.) The material itself will need to be solid at normal temperatures because I honestly doubt they'll try to eat puddles, and convincing them to drink anything other than booze produced from plants has proven difficult in the past.
Indeed it would be dangerous to provide potions that permit fire effects, because it's rather difficult to convince a syndrome to prevent an individual from combusting when exposed to flames because you cannot select materials or tissues, or use just about any tag with a variable. You can make them FIREIMMUNE, but they can still catch on fire, and when the effect wears off they will promptly burn and die.
However, potion of value would be a potion that drastically increases recuperation and disease resistance to be stored near the hospital and fed to patients. And for military use, anything long-lasting that increases other attributes or adds NOPAIN.
In this way, players could restrict soldiers to using a potion stockpile from which they will take their meals, with the effects lasting long enough that they will likely be active during combat. Or if a potion is easy enough to produce and non-intrusive/beneficial to civilian life, they can be stored in any stockpile.
A potion that causes horrendous were-beast transfromations when your soldiers become enraged/enter a trance (without the CRAZED tag so your troops don't kill one-another) would also be cool.