Almost anything with water in it, with three real exceptions. The useful question is not what is possible but what is worth doing.
The categories where the process earns its cost.
Fruit and vegetables, prepared meals, dairy, raw meat and pet treats, botanical extracts and actives, cultures and probiotics, coffee and beverage concentrates, and candy — which works for the opposite reason to everything else on the list.
The common thread in most of them: water to remove, structure worth keeping, and a market that pays for the difference.
Freeze drying removes water. If water is not the problem, it is not the answer.
Pure fats and oils. Butter, oil, chocolate. No meaningful water to remove, so nothing happens.
Very high sugar syrups. Honey and jam do not freeze into a solid ice structure to begin with, so there is nothing to sublime from.
Anything where the structure is the value and the structure is already dry. Nothing to gain.
High-fat products dry, but their shelf life is capped by rancidity rather than by moisture — which is a different limitation from "it does not work."
This is the commercial test, and it is arithmetic.
A product at 90% moisture gives up nearly all its weight as water — a long cycle, high condenser duty, and a dramatic finished product. A product at 15% gives up very little, so the cycle is short and the transformation is subtle unless expansion is the point, as with candy.
Run yours on the water load calculator and the economics answer themselves. Typical starting moistures by category are in the moisture reference table.
Pure fats and oils such as butter and chocolate, because there is no meaningful water to remove, and very high sugar syrups like honey and jam, because they do not freeze into a solid ice structure to sublime from.
Yes, and raw pet treats are one of the fastest-growing categories. The limit is fat: freeze drying removes water but does nothing about lipid oxidation, so high-fat products are shelf-life limited by rancidity rather than by moisture.