This usually involves increasing the temperature and lowering the pressure to provide enough energy to break down the molecular bonding. Removal of the water in this final stage will be performed at higher product temperatures, consequently, any biological activity of the sample will not be impaired or affected. This water has invariably a vapour pressure lower than that of water in its “free” form. Secondary Drying (Adsorption) Phase: Finally, any residual water present, which is strongly bound to the molecules of the sample, is converted to vapour and removed from the sample.
If too much energy (heat) is applied to the sample during this stage the condenser may not be able to condense the volume of vapours fast enough, the ice condenser temperature will subsequently rise along with its vapor pressure, thus increasing the risk of the sample melting. The “energy” required for this process to occur is provided by a gentle heating of the sample, which will start the sublimation process and eventually the sample will dry. The vapour is thus converted back to ice on the condenser surface. The resultant vapour is collected in the condenser, which has a lower temperature and pressure than the product. The ice formed in the pre-freeze step is removed from the sample by the direct transition of the “solid” ice to a vapour without passing through a liquid phase. Primary Drying (Sublimation) Phase: In the second stage the sublimation process starts. Slow pre-freezing will produce larger ice crystals, which are easier to freeze dry, whilst fast pre-freezing results in smaller crystals. Freeze drying can be used to preserve pet food without adversely affecting the quality if the pet food.įreezing Phase: The sample is frozen, which means the water in the product is converted to ice, thereby the phase has changed from liquid to solid. Regular drying can affect quality and impact nutrition. Pet Food – Removal of moisture is important for long term preservation of petfood.Taxidermy – Freeze drying can be used to aid taxidermy.Floral – The moisture content in flowers can be eliminated by freeze drying while still preserving is shape, structure and quality.Document Recovery – Freeze drying can be used for recovery and saving documentation damaged by water, fire etc.Laboratory samples that can be preserved by freeze drying include active pharmaceuticals, pathological samples, microbial cultures, viruses, bacteria, antibodies etc Research – Botanical samples are preserved by freeze drying for research purposes.
Pharmaceuticals that are freeze dried include proteins, antibiotics, hormones, vaccines, plasma etc. It can be reconstituted when ready to use. A liquid drug can be converted to a powder form and stored in a vial. Pharmaceuticals – Increase shelf life of drugs and vaccines.Freeze drying enables the culture to be more effective. Regular drying will decrease efficiency and may cause adverse changes to starters and cultures. Starters and Cultures – Eg, Probiotics, Buttermilk.Freeze drying promote stabilization and shelf-life Nutraceuticals – Nutraceuticals are products derived from food that can be used to promote well-being Eg Aloe Vera, Tea, Sea-weed.
This is advantages because it does not require additional chemical additives and volume of product is reduced enabling easier transportation.
Food Industry – Food freeze dried so that it can be preserved for long periods.The integrity of the sample’s biological and chemical structure remains intact due to the minimal heat input. Along with the minimal heat input that is required, this method is ideal for long-term preservation. Freeze Drying is a process in which a completely frozen sample is placed under a vacuum in order to remove water or other solvents from the sample, allowing the ice to change directly from a solid to a vapor without passing through a liquid phase.
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