Pure fats, oils, honey, jam and anything mostly sugar syrup will not freeze dry, because there is no free water to sublimate. High-fat foods technically dry but go rancid within a year or two, which wastes the cycle. And nothing spoiled goes in — drying preserves what you put in, including bacteria.
The absolute no list
| Food | Why not |
|---|---|
| Butter, lard, cooking oil | No free water. Nothing to sublimate |
| Honey, syrup, molasses | Sugar binds the water. It will not dry and it fouls the chamber |
| Jam, jelly, preserves | Same as honey |
| Peanut butter and nut butters | Almost entirely fat |
| Avocado | High fat; goes rancid fast and the texture collapses |
| Olives in oil | The oil is the problem |
| Anything already spoiled | Drying makes pathogens dormant, not dead |
The technically-works-but-do-not-bother list
- Very fatty cuts of meat. They dry. They then go rancid in a year, and you have spent 30 hours of machine time on food with a shorter shelf life than the freezer would have given it.
- Nuts and seeds. High fat, and they are already shelf-stable for a year or more as they are. There is nothing to gain.
- Chocolate. Blooms, goes chalky, and the cocoa butter oxidises.
- Hard boiled sweets. Barely any trapped moisture, so almost nothing happens.
- Bread. It works, but it rehydrates to something unpleasant. Dry the ingredients instead.
- Whole eggs in shell. Stated for completeness. Blend them first.
The rule that covers all of it
Freeze drying removes water and nothing else. So ask two questions of any food: does it contain free water, and what is left behind when that water is gone? If the answer to the first is no, it will not dry. If the answer to the second is mostly fat, it will dry and then spoil.
The mess cases
Honey and syrup deserve a specific warning because people try them. Under vacuum they foam, creep and end up coating the inside of the chamber and potentially reaching the pump. Cleaning that out is unpleasant and, if it gets past the chamber filter, expensive. It is not worth finding out.
What to do with fatty food instead
- Freeze it. Fat freezes well and the freezer is the right tool.
- Render and jar it. Rendered fat keeps for months at room temperature and years refrigerated.
- Dry the lean part separately. Trim the fat off, dry the lean meat, and store the fat another way.
- Buy it shelf-stable. Oils, nut butters and honey are already long-life products. There is nothing to improve.
One exception worth knowing
Small amounts of fat within an otherwise lean food are fine – a lean stew, whole eggs, skimmed milk. It is a spectrum, not a switch. The shorter shelf lives in our storage guide reflect exactly this.