Vacuum Pressure and mTorr in Freeze Drying

Vacuum pressure is what allows freeze drying to work. When pressure is low enough, ice can sublimate instead of melting. Freeze dryers often show pressure in **mTorr** (millitorr). A torr is a unit of pressure, and a millitorr is one-thousandth of a torr. These tiny numbers matter because freeze drying requires a deep vacuum. During a normal run, pressure often settles into a working range (commonly a few hundred mTorr, depending on machine and conditions). As water leaves the food, the vacuum pump must remove vapor. If vapor removal is slow, pressure rises and sublimation slows. Common causes of high pressure include vacuum leaks, pump issues, contaminated pump oil, and excess moisture load or ice buildup. Watching pressure trends can help you catch problems early. A stable vacuum supports faster drying and more consistent results.