BETTER LOOK, BETTER FLAVOUR, BETTER FOR YOU
Freeze drying is the process of drying frozen raw material under vacuum conditions in which the ice in the material turns directly into vapour (sublimation). A typical sublimation point in the process is -20°C. this means the material goes from one preserved form (frozen) to another (freeze dried) at a very low temperature, and the chance of chemical reactions during drying (which might affect the flavour, nutritional, or bioactive properties) is kept to a minimum.
Therefore product characteristics when rehydrated are closer to those of the raw material than would be the case with other drying technologies, and the dried product is presented to the customer in a convenient form. Rapid rehydration, attractive appearance, better flavour and nutritional quality are some of these characteristics. Biologically active materials e.g. cultures, enzymes, are preserved better; and can be sold in a convenient powder form, unlike frozen materials which are not always easy to use and will deteriorate rapidly if the cold chain is not maintained.
IT COSTS LESS WITH FDF
Freeze Dried Foods New Zealand Ltd (FDFNZ) has developed an efficient freeze drying process to reduce some of the costs often associated with the process. Energy and labour costs have been reduced relative to traditional freeze drying by automated product handling, including tray loading and unloading, by accelerating the process, and using continuous drying technology. Although capital costs are still high on a throughput basis relative to other preservation technologies, the high throughput driers give a lower capital component of costs than traditional freeze driers.
WE CAN PROCESS MORE
The high output of the driers means that relatively large tonnages of products are possible, which would have required considerable capital expenditure with traditional driers and would also have required large factories to house the numerous machines and support systems. For example a standard FDFNZ machine will produce the equivalent of about 5 one-tonne tray freeze driers, using a similar footprint to one one-tonne drier. (A one-tonne drier dries one tonne of frozen material per day.)
SOLID OR LIQUID
FDFNZ has also developed technology to freeze liquids into a suitable form for freeze drying. Traditional tray drying technology means liquids are frozen on trays before being dried. This is slow, expensive and labour intensive, and leads to difficulty in handling product at the end of the process. FDFNZ’s process freezes the liquids into particulates suitable for loading in to driers without manual handling.
This opens up opportunities in development of added-value products with better characteristics than for example spray dried products, but with a lower production cost than traditional freeze driers. It should be noted that unless there is a quality advantage in freeze drying, these products will never compete on price with spray dried products (e.g. milk powders) other than specialised short-run products where there is a large opportunity cost using large throughput machines. The freeze drying process will always be measured in hours compared to seconds or minutes with other processes.
UNDERSTANDING THE COST
In considering whether freeze drying is a viable process there are some guidelines which should be used. Freeze drying costs are generally calculated on the basis of frozen raw material input. This is because yield has a large effect on the cost of the finished product. The yield is related to the solids of the ingoing frozen raw material.
CALCULATING YIELD - SOME EXAMPLES
For example frozen strawberries might have a solids content of about 10%. The yield of dried product for practical purposes here can be considered to be 10%. Therefore if the cost of the frozen strawberries was $3 per kg and the cost of freeze drying was $3 per frozen kg, the cost of the dried strawberry in bulk would be $60 per dried kg.
Cost per dried kg = ($3+$3)/10% = $6/0.1 = $60
On the other hand a meat product might have a solids content of 25%. Using the same input cost of $3 per frozen kg of raw material and $3 per frozen kg to freeze dry, the cost per dried kg in bulk form is $24.
Cost per dried kg = ($3+$3)/25% = $6/0.25 = $24
This gives an idea of some of the range of costs possible. The raw material cost is obviously subject to tonnage, availability, market demand and complexity of preparation and freezing processing prior to freeze drying. The cost of freeze drying is subject to the following: