Oil-filled vs oil-free pumps
Oil-filled is cheaper and reaches deeper vacuum. Oil-free needs no maintenance and is quieter. The five-year cost depends entirely on the oil interval.
Vacuum pump oil: which type, how often, why it matters
Use the specified grade, judge by colour rather than counting cycles, and change it warm. Milky oil is water and it is not lubricating.
Rehydrating freeze-dried food: ratios and soak times
Add 80% of the water you removed, warm not boiling, and wait two to five minutes. Start lower and add - you cannot take water back out.