flask ampules or vials are individually attached to the ports of a manifold or drying chamber. the product is either frozen by direct submersion in low temperature bath, or by shell freezing, depending on the nature product and to volume to be freeze dried. the prefrozen product is attached to the manifold quickly to prevent warming. the vacuum must be created in the product container quickly, and the operator relies on evaporative cooling to maintain the low temperature of the product. this procedure can only be used for small volumes and products with high eutectic and collapse temperature.