Evolution of laboratory freeze-dryers

Tray-based freeze-dryers were formerly heated by means of electrical wires, the temperature being controlled by using a thermostat. The temperature of the shelves (or the product itself) was measured with thermocouples furnished with analogue indicators. 

Pressure measurements were read off a mercury gauge. These obsolete devices were not precise enough for control and measurement purposes or were cumbersome to use. 

Freeze-dryer controls have experienced the most dramatic developments in recent years. The original mercury gauge and thermostatically controlled heaters were initially replaced with analogue vacuum gauges, thermocouples and controls. Eventually, the latter two were superseded by digital devices. 

The thermostatically controlled heaters formerly used in tray-based freeze-dryers were gradually abandoned as they resulted in inconsistent product temperatures. Most freezers of this type currently use hollow trays through which a heat transfer liquid is passed at a controlled temperature. 

Operating currently available freeze-dryer models is less labour-intensive also, modern equipment affords the implementation of some initial production stages. Once the few sample (melting point) and protocol data (final tray temperature) required is input by the operator following insertion of the product, the apparatus conducts an entire freeze-drying 

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