What is freeze drying used for?
Freeze drying has many applications including:
- Long shelf life pharmacutical products.
- Creation of dehydrated powders for tablets or capsules.
- Production of chemically stable bulk raw materials.
- Probiotic powders, protein powders, other food supplement powders.
- Extended shelf life, low weight food rations such as military rations, climber rations and astronaut meals
- Purification and concentration of heat sensitive materials or low molecular weight chemicals
- Advance ceramic powders
- Recovery of water damaged documents and books
- Achaeological recovery and conservation
What advantages does freeze drying have over other drying processes?
Low processing temperatures ensure that nutrients and colour are not lost and proteins are not denatured.
The original shape of the product is kept after the process without shrinkage or toughening.
The product is easily rehydrated due to micropores created by the sublimation of ice from the product.
What capacity do I need?
Your required capacity depends on how much ice you will be removing over a set period of time. When contacting us you should state the “wet” (undried) weight of your product and the timeframe for drying. Our food and industry machines are rated for “x”kg of ice per 24hours, though cycle times are easily adjustable by the user.
How can I tell when the primary drying stage is complete?
1) Product temperature monitoring – monitor the product temperature with a thermocouple – when primary drying is complete the product temperature will rise and approach the shelf/chamber temperature due to the loss of sublimation cooling. When the product and shelf temperature are roughly equal (temperature difference, ΔT around 3-5°C), the primary drying phase can be assumed to be complete. The user should be aware that due to heat conduction through the thermocouple, the area around the thermocouple will dry faster than the bulk of the product and a safety margin for additional primary drying should be included. The thermocouple should also be placed at the bottom of the product as the product will dry from top-down.
2) Pressure Rise Test – If the freeze dryer has an external condenser, a pressure rise test can be used. The isolation valve between the condenser chamber and the product chamber is closed and the pressure rise in the product chamber is measured. If the pressure rise approaches zero, then there is little to no vapour produced by sublimation and the primary phase can be considered complete.
3) Capacitance manometer vs Pirani guage convergence test. This requires both a capacitance manometer and pirani guage to be fitted, as a pirani guage shows erroneously high readings in the presence of vapour, the difference in readings between the two can be used to determine the pirmary drying endpoint. When the two readings have converged (and no further change in the readings is noted) the primary drying phase is complete.
How cold do I need my freeze drier to be?
Extra cold condensers are only required if using solvents with a particularly low freezing point. A phase diagram for your solvent can be used to determine an appropriate condenser temperature. Bear in mind that some organic solvents may cause serious issues with standard sealing materials and should be mentioned in a list of requirements. An excessively cold condenser will increase the cost of the machine as well as it’s complexity!
Where can I keep a freeze drier?
A freeze drier with air cooled condensers should always be kept in a cool, well ventilated room. High ambient temperatures will reduce performance and efficiency and possibly lead to the failure of the unit!
A freeze drier using chilled water for cooling can be located anywhere indoors with adaquete space, though excessive ambient temperatures should still be avoided. The chiller should be located as per the manufacturer guidelines – typically in a cool, outdoor area with plenty of ventilation.